THE RENAL EXCRETION OP SODIUM AND POTASSIUM IN THE DOG* 
by 
D, Baldwin, 1st Lt., M.C., E, M, Kahana, M.D., Physiologist and 
R. W, Clarke, Ph.D., Physiologist 
from 
Medical Department Field Research Laboratory 
Fort Knox, Kentucky 
25 February 1949 
*Sub-project under Studies of Body Reactions and Requirements under 
Varied Environmental and Climatic Conditions. Approved 31 Nay 1946. 
M.D.F.R.L. Project No. 6-64-12-06-(17). Project No. 6-64-12-06 
Sub-project MDFHL 06-(17) 
MEDEA 
25 February 1949 
ABSTRACT 
THE RENAL EXCRETION OF SODIUM AND POTASSIUM IN TOE DOG 
OBJECT 
Studies were carried out on unanesthetized dogs to determine some 
of the factors controlling the fraction of filtered sodium and potassium 
reabsorbed by the renal tubules. The interference with the reaboorption 
of each of these ions by the other and the phenomenon of tubular secre- 
tion of potassium were investigated. Filtration rate (as measured by 
inulin and creatinine clearance) and effective renal plasma flow (as 
measured by sodium para-aminohippurate clearance) were determined before 
and during the intravenous infusion of 0.9$ NaCl, 10$ NaCl and 1.2$ KC1 
solutions. The percentage of filtered electrolyte reabsorbed for both 
sodium and potassium was measured, and the serum concentration of each 
ion was allowed to vary over wide ranges while that of the other ion 
remained at normal levels. 1.2$ KC1 solution was also infused into 
dogs previously fed KC1 for a week. 
RESULTS AND CONCLUSIONS 
The percentage of filtered sodium which is reabsorbed by the tubules 
is functionally related to the serum sodium concentration. The percentage 
of filtered potassium which is reabsorbed by the tubules is related to the 
rate of filtration of potassium. The presence of the chloride salt of 
each ion in the glomerular filtrate depresses the reabsorption of the 
other ion. The ingestion of potassium chloride prior to the infusion of 
this salt augments the depression of potassium reabsorption which noriaally 
follows an increased filtration of potassium. 
RECOMMENDATIONS 
Investigations should be carried out to determine the other factors 
which regulate the fraction of filtered sodium reabsorbed by the renal 
tubules. The mechanism of tubular secretion of potassium should be 
studied further. 
Submitted by: 
D, Baldwin, 1st Lt., M.C, 
E. M, Kahana, M.D., Physiologist 
R. W« Clarke, Ph.D., Physiologist 
Approved 
RAY (/ (J 
Director of Research 
Approved^ 
FRSEERICK J. KNOBLAUCH 
Li. Col., ii.C, 
Commanding THE RENAL EXCRETION OF SODIUM AND POTASSIUM IN THE DOG 
I. INTRODUCTION 
The observation that the intravenous infusion of 10% sodium chloride 
solution produced in the dog a marked potassium diuresis led to tnis 
investigation. Such an observation is by no means unique. Wolf (l?) has 
shown in man that the intravenous infusion of hypertonic sodium chloride 
solution effected a greater potassium excretion than the infusion of 
hypotonic solution. Stewart and Rourke (13), studying the effects of 
intravenous infusions in man, have shown that 0.9% saline solution pro- 
duced a greater excretion of potassium than 5% glucose solution. Simply 
by the ingestion of sodium chloride, the rate of potassium excretion in 
man is increased, as pointed out by Gamble (5). Conversely, the infusion 
of potassium sulfate solution has been shown by Schwartz, Smith and Winkler 
(12;, to produce a diuresis of sodium in dogs. 
All these phenomena are not confined to the cations, Fitts and 
Lotspeich (ll) have clearly demonstrated the significance of a similar 
relationship among anions in the regulation of the acid base balance. 
The increased reabsorption of chloride lowers the capacity of the renal 
tubules to reabsorb bicarbonate and produces an increased excretion of 
this ion. Conversely, the increased reabsorption of bicarbonate dimin- 
ishes the tubular reabsorption of chloride, Schwartz, Smith and Winkler 
(12) have claimed that increased excretion of sulfate will increase the 
tubular reabsorption of chloride in spite of a rising serum chloride 
concentration. Their evidence shows that chloride excretion is repressed 
by sulfate excretion. Lotspeich (8) has demonstrated evidence in dogs 
of a tubular maximum for sulfate reabsorption by injecting sodium sulfate 
solution intravenously, elevating the plasma sulfate concentration, and 
saturating the renal tubules with this ion. When hypertonic sodium 
chloride was added to the sodium sulfate infusions, the rate of tubular 
reabsorption of sulfate was markedly reduced from the maximum values 
attained with sodium sulfate alone, Maximum levels of tubular reabsorption 
have also been demonstrated for phosphate (?, 10). The rate of reabsorp- 
tion of these ions cannot be increased beyond these maximum levels by 
increasing the filtered load. 
In exploratory experiments, in this laboratory, the rates of tubular 
reabsorption of sodium and potassium were found to vary widely when dif- 
ferent concentrations of sodium chloride and potassium chloride were 
infused intravenously in dogs. No obvious pattern of reabsorption was 
apparent. Consequently, the premise was adopted that for any given quan- 
tity of sodium or potassium filtered by the glomeruli per unit time, the 
fraction reabsorbed could be predicted, provided the factors regulating 
this fraction were known. 
The purpose of this investigation was to determine some of the factors 
controlling the fractional reabsorption of sodium and potassium. Evidence 
of maximum tubular reabsorption of sodium and potassium was sought, and 
the raitual interference with reabsorption by these ions was investigated. 
The percentage of filtered electrolyte reabsorbed for both sodium and 
potassium was measured, and the serum concentration of each ion was allowed 
1 to vary over wide ranges while that of the other ion remained at normal 
or nearly normal levels. Renal plasma flow was measured in addition to 
filtration rate in an attempt to demonstrate qualitative changes in 
renal hemodynamics following the infusion of sodium and potassium chloride 
It also proved necessary to study the phenomenon of tubular secretion 
of potassium in order to formulate valid conclusions as to the effect of 
sodium chloride upon the reabsorption of potassium. It appeared reason- 
able to believe that undetermined potassium secretion might well invali- 
date any estimations of potassium reabsorption. 
II. EXPERIMENTAL 
A. Methods 
A series of 28 experiments was carried out on 6 trained un- 
anesthetized female dogs. These were used in a post-absorptive state 
and were lightly restrained, supine on a dog-board. Following the with- 
drawal of a blood sample, subsequently to be used as a blank in the 
various chemical analyses, a mixture containing 0,2 ml. of a 205b sodium 
para-aminohippurate solution and 2.5 ml. of a 105© inulin solution, each 
per kilogram of body weight, was injected into the loose, areolar tissue 
of the axillae. Inulin was used exclusively to measure filtration rate 
in the first 12 experiments. After inulin and creatinine clearances had 
been determined simultaneously in 3 experiments, and it was established 
that the inulin/creatinine clearance ratios consistently ranged between 
0.92 and 1.00, creatinine was substituted for inulin. Purified creat- 
inine (0.25 gm. per kilogram body weight) was dissolved in 30.0 ml. of 
distilled water, and para-aminohippurate solution was added before 
injection. After a 20-minute period, 25 ml. of water per kilogram body 
weight were administered by stomach tube, followed by the installation 
of a silk-woven catheter into the bladder. 
One or more control experiments without infusion were carried 
out on each of the 6 dogs. Intravenous infusions were started in every 
instance from 5 to 10 minutes before zero time which was established as 
30 minutes after the subcutaneous injection. The solutions of NaCl and 
KC1 were administered according to the following schedule: 
10$ NaCl: Continuous intravenous infusion of a 10$ solution 
at a rate of 2 to 5 ml,/min, 
0,9$ NaCl: Continuous intravenous infusion of a 0,9$ NaCl 
solution at a rate of 1 to 3 ml./min, 
1,2$ KC1; Continuous intravenous infusion at rates ranging 
from 2,5 to 6,0 ml./min., varying the rate with individual experiments 
and from period to period, 
1.2$ KC1 following KC1 feeding: Continuous intravenous 
infusion as above, following the administration in the diet of 5 grams 
of potassium chloride given twice a day for one week. 
2 Following the initiation of the infusion, 3 to 8.consecutive clear- 
ance periods of 15 to 20 minutes in length were measured. Clearance 
periods and the drawing of blood samples were timed to the nearest tenth 
of a minute. Blood samples were drawn from the external jugular veins at 
a time approximately minutes before the midpoint of the anticipated 
length of the period for which these amounts were timed. The bladder was 
washed at the end of each period with 20 ml. of distilled water followed 
by the injection and withdrawal of 20 ml. of air. After the period had 
been timed, an exact moment minutes before the midperiod was calculated; 
and at the conclusion of the analyses the actual plasma and serum concen- 
trations at these times were obtained by interpolation. Inasmuch as the 
plasma concentrations of all substances studied changed at small and 
fairly uniform rates, the values used in the calculations properly repre- 
sent the composition of the blood from which each urine sample was formed. 
Analyses for inulin and para-arainohippurate (PAH) were carried out 
on heparinized plasma and diluted urine samples according to the methods 
of Harrison (6) and Smith al. (14), and for creatinine according to the 
modified alkaline picrate procedure of Brod and Sirota (2)• Sodium and 
potassium determinations were made on diluted serum and urine samples with 
a Perkin-Elmer Flame Photometer (Model 52-A) utilizing an internal lithium 
standard of 20 mSq/L. Blood for serum analyses was collected under mineral 
oil and centrifuged shortly after clotting. The serum was diluted 100 
times with distilled water. Urine samples were diluted from 5 to 200 times 
depending upon the anticipated concentration of the cation. A maximum 
sodium standard of 2 mEq/L was used throughout for both serum and urine 
samples. Maximum potassium standard utilized for sera was 0.1 mEq/L; for 
urine 0.4 mEq/L. Studies with urine and serum samples revealed an accuracy 
of about 1% for sodium determinations, about l+% for serum potassium, and 
about for urine potassium determinations. 
The data were corrected for surface area according to the formula 
0.112 x weight (kg.)2/3 , in order to minimize partly the differences 
inherent in the use of dogs of different size. 
Excreted electrolyte was calculated by multiplying the urine con- 
centration of the ion by the actual urinary output per minute. 
Filtered electrolyte or filtered load was calculated by multiplying 
the serum concentration by the inulin or creatinine clearance. 
Reabsorbed electrolyte was calculated by subtracting the excreted 
electrolyte from the filtered electrolyte. 
The percentage of filtered electrolyte that was reabsorbed, expressed 
by the function t/L, was obtained by dividing the t or reabsorbed elec- 
trolyte by the L, or filtered electrolyte and multiplying by 100. Negative 
values for the t/t function indicate a greater excreted electrolyte than 
a filtered electrolyte, with a resulting negative value for reabsorbed 
electrolyte. 
3 3, Results 
1. Control Data: 
The control data comprised 42 clearance periods (measured 
on 6 female dogs). From these, the following observations were made (see 
Table 1 for control data on 2 of the dogs): 
a. There were wide differences in the renal plasma flow. 
PAH clearance values corrected for surface area ranged froa 124 to 295 
ml./min., with mean values for all periods of 209. 
b. Inulin or creatinine clearance values corrected for sur- 
face area ranged from 41.6 to 91.5 ml./min. with a mean value of 67.6, 
c. Filtration fractions remained moderately constant, ranging 
from 0.24 to 0,36, and in no instance varied more than J 0.04 during the 
course of a single control experiment. 
d. Sodium filtered through the glomeruli was reabsorbed 
almost completely, the percentage of reabsorption (t/L Na) varying from 
98,8% to 99.9% with a mean value of 99.6%. 
e. '•'he percentage of filtered potassium reabsorbed was less, 
ranging from 79.7% to 96.0%, with a rasan value of 90.5%. 
2. Sodium Injection: 
a. 0.9% NaCl! Two experiments comprising a total of 8 
clearance periods gave the following results (see Table 1): 
(1) The intravenous infusion of 0,9% NaCl raised the 
mean value for renal plasma flow, although individual 
measurements were widely scattered, PAH clearances 
corrected for surface area rose to a range of 218 to 
399 ml./min. 
(2) The filtration rate rose to a range of ©3.9 to 94.8 
ml,/min, 
(3) The serum sodium concentration gradually rose to a 
range of 143 to 151 mKq/L. 
(4) The percentage of filtered sodium reabsorbed (t/L Na) 
fell slightly in both experiments, 
(5) The serum potassium concentration was slightly 
depressed. 
(6) The percentage of filtered potassiuin reabsorbed 
(t/L K) was slightly depressed in both experiments 
by the end of the fourth clearance period, approxi- 
mately 80 minutes after the beginning of the infusion.  
Period 
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5 (7) There was a significant increase in the rate of 
excretion of potassium, due both to the rise in fil- 
tration rate (serum K being constant) and to the fall 
in t/L K r/hich approximated the simultaneous fall in 
t/L Na (see Table l). 
b. 10$ NaCl: The effect of an infusion of 10% NaCl upon the 
excretion of sodium and potassium was studied in 5 experiments, comprising 
a total of 19 clearance periods. The data from 2 experiments are given in 
Table 1. From these data, the following observations were made: 
(1) 10$ NaCl raised the mean value for renal plasma flow 
considerably although individual measurements were 
widely scattered, PAH clearance values corrected 
for surface area tended to rise to a range of 192 to 
473 ml,/min. 
(2) Filtration rate also tended to rise to a range of 
74.3 to 151.0 ml./min. 
(3) Parallel increases in both of these measurements 
maintained a relatively constant filtration fraction. 
In no instance did this vary more than i 0.09 during 
the course of a single experiment. 
(4) In all cases the increase in renal blood flow and in 
filtration rate roughly paralleled the increase in 
serum sodium concentration which reached a maximum 
in the last period of each experiment (see Figure l). 
(5) The filtration, reabsorption, and excretion of 
sodium and potassium were markedly increased by the 
infusion of 10$ NaCl, 
(6) The percentage of filtered electrolyte reabsorbed 
(t/L; fell markedly for both sodium and potassium; 
t/L Na values fell as low as 70.9$ and t/L K values 
as low as 11.6$. 
The rise in filtration rate increased the filtered load 
of potassium in spite of the fact that the serum potassium concentration 
was depressed to low values early during the infusion of hypertonic saline. 
This rise, coupled with the low values of the t/L K, effected a marked 
increase in the excretion of potassium. The increased excretion of sodium 
in no instance was accompanied by a depression of the t/L Na value equal 
to that of the t/L K. 
Hxaraination of Figure 1 reveals that the rise in serum 
sodium concentration was in most instances associated with a rise in the 
filtration rate, .Although the serum sodium concentration rose as much as 
50 mSq/L, and the sodium filtered load was doubled (see Table l), the rate 
of reabsorption of sodium showed a continued rise. There was no evidence 
of the existence of a tubular maximum for socium. 
6 FIG 2 FILTRA'ION RATE AND Rf‘.AL PLASMA FLO* PLOTTED AS FUNC'CNS OF 
THE SERUM POTASSIUM CONCENTRATOR The lag* of corre.a* ON of 
these functions is clear 
* . RA'r. AN REKA,. PlASVA -\CA PLOTTED AS FUNCTlONS OF th£ 
S:JLV .. „v .CCtN'RAT ON SEROV SODioM CONCENTRATION WAS ELEva*EO 
Si -.-I '-.s OF 051 ADD .0% SOOtVW CHLORIDE FIG 4 POTASSu>M REABSORBED PLOTA •■. .• •• - 
filtered the scat-e* cf -he .cfosico ca*a s c..e.-.« *■•• 
L -.E ME AS .PEE COMPLETE RE ASSORT-" ON , TP A t ,t. 
■ 3 .5 "“t C-- see .V eEA8SCRF*'0’. F^:'TE: a_ A Fcr.C'C'. CF T-£ RA*£ 
• -~ 3*. T-s cf ic % sacne C4t: .e clear --£ 
••■ ■*— ■<£ '-'E-S 5! .evRuETE »EA8‘..f.o* CO, Ci A t/L .■• LcE C* Fig. 6 THE PERCENTAGE OF P'LTEpeC SODiuM R£ absd pHE C it . ; lCT*: ’ - 
A FUNC* CM OF THE SEPUM SODIUM C L MCE MTR A’ IQM AM APP»C» '.’ATE. I 
t'KEAR RELATIONSHIP IS ShOVUM CCRPElAT.ON COEFFICIENT »: u • ; 
DA*A •- C 94 
F r '-E FE'-\-;>.U5E Oc F.LTEREO SCOlUM REABSORBED (t/L N, ) PLOtT£D AS 
A Cc SODi. V FILTERED THE COMPLETE SCATTER OF THE SALINE 
-S . •. CA'A s C L £ A° 
9 As can be seen in Table 1, the rate of sodium excretion 
and sodium clearance became elevated as the serum sodium concentration rose. 
The serum potassium, on the other hand, never attained hyper-normal levels 
and yet potassium excretion and potassium clearances were also increased. 
//lien sodium reabsorbed was plotted against sodium fil- 
tered (see Figure 3) from control experiments only, inasmuch as reabsorp- 
tion was practically complete, the data provided a linear graphic relation- 
ship between these two quantities. However, this was not maintained in 
animals inTused with 0.9$ NaCl and 10$ NaCl solution. These points, each 
of which measures a t/L Na, scattered apparently at random. Upon in- 
spection of tliis graph, it may be seen that a few of the hypertonic saline 
points overlap normal saline data and controls. At the same filtered 
sodium load, the reabsorption of sodium varied quite markedly in the 10$ 
NaCl and 0.955 NaCl experiments. Analysis of the overlapping data reveals 
that the distinguishing difference between any 2 points which represent 
unequal rates of reabsorption at the same filtered load was the serum sodium 
concentration. The higher the serum sodium level, the farther away were the 
points from the line measuring complete reabsorption of filtered sodium. 
The t/L Na was plotted against sodium filtered, serum sodium concentration ■ 
and filtration rate in an attempt to corroborate this analysis. The rate 
of filtration of sodium and the serum sodium concentration are presented 
in Figures 5 and 6, Change in filtration rate showed no correlation with 
the t/L Na. 
Calculation of a correlation coefficient for sodium fil- 
tered was considered useless in view of the marked scatter of the data. 
Calculation of the correlation coefficient between the t/L Na and the serum 
sodium concentration gave a value of 0*%. The graph (Figure 6) illus- 
trates an approximately linear correlation between the t/L Na and the serum 
concentration. All K)$ NaCl and 0,9$ NaGl experiments providing the data 
portrayed in tills graph showed a steady rise in the serum sodium concentra- 
tion, Depression of the t/L Na much below 70$ probably cannot be achieved 
hy hypertonic saline infusion technique alone. The serum concentration is 
considered to be the factor which regulates the reabsorptive activity of 
the tubules in regard to sodium. This relationship will be used as a 
standard of reference in the evaluation of the effect of an infusion of 
potassium chloride solution upon sodium reabsorption. 
3, Potassium Injection: 
a. 1.2$ KC1: The following observations are drawn from 
7 infusion experiments comprising a total of 32 clearance periods. Two of 
these experiments are suiomarized in Table 2, 
(l) The renal plasms flow was affected in an irregular 
manner by the infusion of 1,2$ KC1 solution. The 
general trend of all the data suggests that the PAH 
clearance became elevated; but it is impossible to 
draw any further conclusions. 
(2) The effect upon filtration rate was also unpredictable. 
The general trend of all the data again suggests that 
the infusion of KC1 solution was accompanied by a 
gradual elevation of the creatinine clearance. The 
10 rime 
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0.21k 
12 ,91 
1.69 
90.2 
7.0 
0.65 
0.62 
u.03 
08. f? 
3.9 
137-157 
8 
182 
99.9 
.55 
5.1 
Ho 
13.98 
0.31 
13.67 
2.38 
97.0 
6.9 
0.65 
0.67 
0.02 
97.10 
2.2 
Dog C 
— Weight li».5 kg. 
Surface 
area 0.67 — — txperiment 
9. 1.2$ 
KC1 Solution 
0 - IS 
1 
213 
81.C 
.38 
2.9 
HI 
11.1*1 
0.03 
13 .38 
o.22 
99.7 
C 
o .1.3 
0.09 
o.3u 
16.9P 
78.1 
25 - 30 
2 
2l*lk 
96.7 
.1*0 
1*.3 
HI 
13.63 
O.U* 
1..59 
0.27 
99.7 
5.8 
0.56 
0.36 
0.1*0 
27.59 
71.1 
30 - 15 
3 
220 
103.3 
.17 
1.1* 
HI 
H ,56 
0.08 
H.Ub 
0.55 
99.5 
6.1 
o.63 
u.2C 
0.35 
1*5.90 
55.8 
1*5 - 66 
i» 
251 
102.5 
.a 
2.5 
HO 
H.31k 
0.18 
H.36 
1.30 
90.7 
6.1 
o.66 
0H3 
u.23 
67.lv 
35.9 
66-82 
5 
367 
103.0 
.20 
ik.9 
138 
U.21 
0.2v 
13 .92 
2.13 
°7*9 
6.8 
o.?C 
0.57 
u.13 
83.82 
19.0 
Dog C — 
— Weight 16.1 kg. 
Surface 
area O, 
72 arperiment 10. 1.2> 
KC1 Solution following feeding *C1 
0-19 
1 
Ihb 
81.8 
—Ik U 
Ik.7 
H? 
11.62 
O.Ul 
13.61 
0.06 
99.9 
5.2 
o.a 
0.32 
0.31 
23.06 
7? .3 
19 - 39 
2 
221 
79.7 
.36 
5.0 
HI) 
11 .u 7 
O.ul 
13 .1*6 
0.10 
99.9 
6JL 
0.51 
0.17 
0.31* 
26.1*9 
,66.7 
39 - 53 
3 
162 
65.9 
.a 
2.2 
HU 
9.1*9 
0,02 
9.1*7 
o.H 
9V.8 
6.1 
0.i*U 
0,20 
0.2o 
32.79 
1*9.5 
53 - 71 
1 
171k 
66.9 
.39 
1.8 
H3 
9.56 
0.03 
9.r3 
0.22 
9V.7 
5.9 
0.1*0 
u.?? 
0.13 
**5.7c 
33.2 
71-86 
5 
18? 
71.2 
,^8 
1.7 
IH 
10.25 
0.03 
lu.2? 
0.10 
99.7 
6 
o.H 
o.?7 
O.o? 
59.6b 
It .6 
86 -100 
6 
20? 
76.9 
.37 
2.5 
Hik 
11.07 
o.u5 
13.02 
0.30 
99.5 
6.0 
0.1*6 
0.15 
0.01 
75 .<0 
1.9 
1CK-130 
7 
219 
01.5 
.37 
2.3 
HL 
H.7lk 
O.o7 
13 .67 
0.1*7 
99 H 
5.1 
o.U* 
0.18 
C eUl* 
80.89 
- C.c 
130-151 
8 
169 
79.7 
.1:2 
1.9 
H5 
11.56 
o.ul* 
11.5? 
0.2b 
99.7 
5.3 
0.1*2 
0.37 
O'.05 
69.08 
12.3 
TkSlZ ? 
KmssrjM is relationship of the serum potassium to renal plasma 
flow and filtration rat© is portrayed in Figure 2. 
The poor correlation between these functions is 
evident. 
(3) Although the serum potassium was significantly ele- 
vated, as seen in Table 2, in every experiment of 
this type, the serum sodium concentration was essen- 
tially unchanged. 
(4) The t/L K and the t/L Na are depressed in every 
experiment. These values fell in one experiment from 
a control mean value of 925b to 19$ for potassium and 
from 99.8$ to 97*3$ for sodium. The depression of 
the percentage of filtered sodium reabsorbed is slight 
but consistent in each experiment of the potassium 
infusion series, and the infusion of this solution 
produces in every experiment, an increase in the rate 
of excretion of sodium. 
Winkler and Smith (l6) have stressed the fact that the ele- 
vation of the serum potassium concentration relates to the rate of potas- 
sium excretion and the potassium clearance, and that potassium excretion is 
a somewhat different function of serum concentration at high than at low 
serum potassium concentrations. Upon plotting these relationships for the 
experiments on dogs reported here, a similar variation was found between 
experiments, and between individual clearance periods. Analysis of the 
data revealed that this variation was largely ascribable to variations from 
period to period, and day to day in the filtration rate. Table 3 reveals 
the importance of filtration rate In determining the rate of excretion of 
potassium: 
TABLE 3 
(Units as in Table 2) 
DOG A 
Exp. No. 
Period 
GCr* 
Serum K 
Filtered K 
Excreted K 
Reabsorbed K 
7 
2 
9 8.8 
5.3 
0.52 
0.13 
0.39 
11 
3 
34.0 
b.U 
0.54 
0.14 
0.40 
7 
3 
99.9 
5.8 ' 
0.58 
0.24 
0.34 
11 
4 
78.0 
7.4 
0.57 
0.22 
0.35 
Creatinine 
clearance 
Examining the data from two 1,2$ KC1 infusion experiments o 
on Dog A, it will be seen that when filtration rate differs widely, inverse 
values for serum potassium concentration may result in similar rates of 
potassium filtration, excretion and reabsorption. Attempts to relate the 
rate of potassium excretion solely to the serum concentration are not satis- 
factory. The filtration rate plays a major role in the regulation of potas- 
sium excretion. Only a poor correlation exists between serum potassium con- 
centration and filtration rate (see Figure 2). Therefore, both serum potas- 
12 slum and filtration rate act practically independently in the regulation 
of the rate of excretion of potassium. An analysis of the conditions that 
regulate potassium excretion must include both of these factors. 
It has been impossible to utilize, therefore, the relation- 
ship expressed by Vfinkler and Smith (l6) as standards of reference from 
which one might differentiate the effect of sodium chloride upon potassium 
reabsorption. 
Seeking evidence of a tubular maximum for potassium in the 
data (see Table 2), one is confronted with the observation that as the fil- 
tration of potassium increased, the rate of reabsorption rose and then 
rapidly fell in 5 but of 6 experiments. In no instance could a constant 
maximum rate of reabsorption be demonstrated although the serum potassium 
rose steadily in the course of each experiment, and the potassium filtered 
load approximately doubled in magnitude. The gradual depression of the rate 
of reabsorption of potassium in response to an increasing filtration of 
potassium appears to be unique in renal None of the other elec- 
trolytes behave in this fashion and neither do any of the organic substances 
such as glucose, ascorbic acid and the amino acids. The recent work of 
various investigators (l, 9) indicating the existence of the phenomenon of 
tubular secretion of potassium may lend clarity to an analysis of the data 
from these experiments. If the renal tubular system is capable of secreting 
potassium at the same time that it reabsorbs it, simultaneous potassium 
secretion will effect a pseudo-depression of reabsorption. Thus, potassium 
secretion will be deducted from actual potassium reabsorption. If tubular 
secretion attains sufficient magnitude, it may exceed reabsorption and 
effect negative values for computed reabsorption. The existence of a tubular 
reabsorptive maximum for potassium will be concealed by this process. The 
data reveal that a tubular maximum for potassium is possible, providing 
tubular secretion of potassium is postulated. 
i/hen potassium reabsorbed was plotted against potassium fil- 
tered in control experiments only, the percentage reabsorption being prac- 
tically constant, the data provided a roughly linear relationship between 
these two quantities (see Figure 4). However, this relationship was not 
maintained in animals infused with 10% NaCl and 1.2% KC1 solutions. From 
Figure U, it may be seen that when 10% NaCl was infused, the reabsorption 
of potassium varied widely for any filtered load and was depressed below 
control data, When 1.2% KC1 solution was infused, there was a gradual rise 
in reabsorption accompanying a gradual increase in the potassium filtered 
load. With filtered loads of great magnitude, the rate of reabsorption of 
potassium became severely depressed. 
Analysis of the data alone, revealed that the rate of excre- 
tion of potassium is determined by the combination of the serum concentra- 
tion and the filtration rate. Each point on Figure U represents a t/L 
value. In an attempt to determine the factors responsible for this pattern 
in the t/L K, we have plotted t/L K as a function of filtration rate, serum 
potassium concentration and the rate of potassium filtration. Filtration 
rate alone appeared to have no relation to the changes manifested in the 
t/L K following the infusion of KC1. The graphs of serum potassium and fil- 
tered potassium are given in Figures 7 and 8, Calculations of the correla- 
tion ratios for the 2 graphs, analyzing statistically the 1.2% KC1 data 
13 FIG 8 THE PERCENTAGE OF FILTERED POTASSIUM RE ABSORBED (t/I K 1 PLOT’ED AS A 
FUNCTION OF THE RATE OF POTASSIUM FILTRAT'O-. EXCEL. £14? CORRE AT..jN ■ 
CLEAR CORRELAT'ON RATIO FOR KCL NFUSiON D4't =0 91 
? TH€ P t R CENTAGE OF F LTEREO POTASSIUM REABSORBED (t/L K) PLOTTED 
AS A FUNCTION OF SERUM POTASSIUM CONCENTRATION ONLV MINIMAL 
•CRH t . AT'ON .5 PRESEI.T CORRELATION RATO FOR KCl INFUSION DATA=0,5J 
14 only, revealed a value of 0.53 for the serum concentration and 0.91 for 
the filtered potassium graph. Analysis of Figure 7 revealed that the 
scatter is ascribable to the fact that the filtration rate had not been 
considered. Whenever the filtration rate increased in proportion to the 
rise in serum potassium concentration, the t/L K was markedly depressed. 
‘.Then the rate of excretion of potassium was plotted as 
a function of the rate of filtration of potassium, the slope of the result- 
ing curve was identical with the slope of the curve shown in Figure 8, 
This relationship of potassium excreted to potassium filtered was previously 
indicated in an analysis of the data. Inasmuch as the rate of potassium 
reabsorption is, by definition, the difference between the rate of potas- 
sium filtered and the rate of potassium excreted, it follows that the rate 
of filtration of potassium is a function of the rate of reabsorption of this 
ion. Upon reexamining Figure 4, it may be seen that when 102$ KCl solution 
is infused, reabsorption is related to filtration in an unusual manner. 
With increasing filtered loads, reaboorption rises and then falls. Three 
points on the graph lie above an arbitrarily drawn dotted line. These t/L 
values were taken from the same experiment. The usually severe depression 
of the t/L K in response to a rising filtration of potassium was only slight 
In all those points. It is postulated that the phenomenon of tubular secre- 
tion was largely inactive in this experiment. In the rest of the data, the 
severe depression of the rate of reabsorption that followed the elevation 
of the potassium filtered load beyond 0.5 mEq/min/l. in all probability is 
ascribable to tubular secretion and presents a false picture of reabsorption. 
It will be noted that the t/L K is related to a different 
variable factor than the t/L Na. The latter showed a correlation with the 
serum concentration. Studying potassium reabsorption in rats. Dicker (3) 
also concluded that the t/L K is related to the filtration of potassium. 
No exhaustive attempt was made to maintain an absolutely constant potassium 
dietary intake, and the admitted variation of the control data and potassium 
chloride infusion data found in Figure 8 may be ascribable to this fact. 
b. 1,2 KCl following KCl feeding: An investigation of the 
phenomenon of tubular secretion of potassium became essential. With KCl 
infusion experiments, in no instance did the rate of excretion of potassium 
exceed the rate of filtration of potassium. No absolute evidence has there- 
fore been provided in these experiments for tubular secretion of potassium. 
Potassium clearance must exceed filtration rate when t/L K values are 
negative. Various investigators (1, 9) have demonstrated tubular secretion 
by infusing hypertonic KCl solutions into dogs that had been fed additional 
KCl in the diet for a week. 
In this investigation, 10 grams of KC1 were added to the 
diet of each of 4 dogs for one week prior to the infusion of an isotonic 
solution of additional KOI. Four experiments comprising a total of 
28 clearance periods were carried out. In this manner, the depression of 
the rate of reabsorption of potassium which followed the infusion of 1.2^ 
KCl solution could be further studied. The previous ingestion of KC1 
resulted in an increased rate of potassium excretion in each experiment. 
The same irregular rise of filtration rate and irregular response of the 
renal plasma flow was observed as when 102% KCl solution was infused without 
15 FIG.9 THE PF RGEN f AGf OF FILTERED POTASSIUM R! AbSORfaED (I i K) PLOTTED AS 
A FUNCTION Of THE RATE OF POTASSIUM FILTRATION INFUSION W.TH I ?% KC1 
SOLUTION WITH AND WITHOUT PREVIOUS FEEDING OF 10 GRAMS Of KCl DAII < 
FOR ONE W FT K 
16 previous feeding, and the serum sodium concentration was again unchanged. 
The t/L Na showed the same slight depression in every experiment, falling 
in one clearance period to 97.6$ during the infusion of KC1. However, 
the t/L K was greatly depressed. In one experiment by the end of the 
seventh clearance period, this percentage had fallen to Although 
the filtered potassium loads in experiments on Dog A were essentially the 
same whether KC1 had been previously fed or not (see Table 2), the t/L K 
showed a far greater depression in the feeding experiment. In Dog C. 
although the filtered loads of potassium in the feeding experiment were 
all much lower than in the simple infusion experiment, the t/L K values 
for the feeding experiment were depressed far more severely. A marked 
depression of the rate of potassium reabsorption accompanied the rise in 
serum concentration, and the elevation of the potassium filtered load. 
The graph in Figure 9 presents the data from the 1.2$ KC1 
infusion experiments, and the potassium filtered and t/L K data from similar 
infusion experiments after feeding KC1 for one week. 
At the same filtered potassium loads, the t/L K was de- 
pressed far more when 1.2$ KC1 solution was infused into dogs previously 
fed with KC1. Thus the rate of potassium excretion at similar filtered 
potassium loads was increased in KC1 fed dogs. In the data from these 
dogs it was also found that the fairly constant relationship of potassium 
filtered to the t/L K showed greater variation. The four clearance periods 
reporting negative t/L K values provide only presemptive evidence of tub- 
ular secretion of potassium because of the small magnitude of their potas- 
sium to creatinine clearance ratios, which were 1.10, 1.10, 1.03 and 1.03. 
It appears possible that the reabsorption of potassium in clearance periods 
during which the t/L K is positive has been largely masked by the addition 
of tubular secretion. 
A. Sodium and Potassium Excretions 
a. Effect of sodium chloride upon potassium: Upon reexamining 
Figure 1, it will be seen that in most instances, with the infusion of 10$ 
NaCl solution and the associated elevation of the serum sodium, the fil- 
tration rate rises above control values. The elevation of filtration rate 
increases the potassium filtered load in spite of a constant serum potas- 
sium concentration. In evaluating the effect of NaCl upon the reabsorption 
of potassium, this increase in the filtered potassium load must be con- 
sidered. Fig 10 shows the depression of the t/L K as a function of the 
filtered load of potassium. The potassium data from hypertonic NaCl experi- 
ments have been added, The t/L K at any filtered load is generally rraich 
lower in the presence of NaCl, and the rate of potassium reabsorption is 
far lower at any filtered potassium load (see Figure 4 and Tables 1 and 2), 
The infusion of 10$ NaCl appears to depress specifically 
the reabsorption of potassium. 
The effect of 10$ NaCl upon potassium reabsorption was 
investigated further. Graphic analysis revealed that the serum sodium 
concentration appears to be more correlated with the t/L K than with sodiun 
filtered, filtration rate or other sodium variables. This relationship is 
illustrated in Figure 11. SEROV Ha(mE6 / L) 
Fio II THE PERCENTAGE OF FILTERED POTASS 'Old RE ABSORBED (t f L * ! PLOTT EO AS A 
FUNCTION OF THE SERUM SODIUM CONCENTRATION. DATfi rA*FH ? % 
KCF , C.9% N. CJ . AND 10 % .M. Cl INFUSION £ KPERiMEN TS 
K FILTERED (««Eq. / MiN. / M*) 
FIG- 10 THE PERCENTAGE OF FILTERED POTA$SlL'S» REABSORBED (fU. PLOTTED AS 
a function of the ra'e cf oqtassk ' filtration data take . ■... 
1.2 % KCl AND 10'- .. 'jFJSiOS EXPF- VENTS. ;> The depression of the t/L K at normal serum sodium concen- 
trations as seen in Figure 11 in the data from 1*2$ KC1 experiments, is 
effected by increasing the filtration of potassium. 
b. Effect of potassium chloride upon sodium: In the 1*2$ 
KC1 infusion experiments, it was noted that by the end of the third or 
fourth clearance period, sodium excretion showed a marked increase and the 
sodium clearance had risen. This, as has been pointed out, was associated 
with a slight depression of the t/L Na, The effect of KC1 on sodium reab- 
sorption is pictured in the inset of Figure 6 in which the control and 1*2$ 
KCl infusion data have been replotted with decreased dimensions of the co- 
ordinates. The relationship of the t/L Na to the serum sodium concentration 
has been used as a standard of reference to demonstrate the effect of KQ. 
infusion on the reabsorption of sodium. It will be noted that in the pres- 
ence of KCl, the t/L Na data fall below the control data. Although the 
statistical significance of this effect is low, it was completely consist- 
ent in every potassium infusion experiment. 
III. DISCUSSION 
Inasmuch as no analyses for chloride were undertaken in this investi- 
gation, a differentiation between the effect of sodium and of chloride upon 
potassium reabsorption was impossible. Similarly, it was not possible to 
distinguish between the effect of potassium and chloride upon sodium resb- 
sorption. Lotspeich (S) demonstrated an inhibition of sulfate reabsorption 
by sodium chloride in dogs. Increasing the filtration rate by feeding meat, 
he was able to show that increased chloride reabsorption in the absence of 
a 10$ NaCl infusion did not depress the simultaneous reabsorption of sulfate. 
He concluded that the decrease in the tubular reabsorption capacity for 
sulfate was a "non-specific osmotic effect" consequent upon the appearance 
of large quantities of sodium and chloride ions in the glomerular filtrate. 
Our experiments were designed to explore the possibilities of a tubu- 
lar maximum for sodium and potassium. Wo such reabsorptive limit for sodium 
was demonstrable under the conditions o£ the experiments. The tubular maximum 
for potassium, if present, could well be /aasked by tubular secretion of potas- 
sium. It is impossible at the present time to determine whether the effects 
portrayed within this paper were "non-specific osmotic effects". The inhi- 
bition of potassium reabsorption by sodium chloride infusion and the inhibi- 
tion of sodium reabsorption by potassium chloride infusion may well exempliiy 
the mechanism of bicarbonate and chloride reabsorption delineated by Pitts 
and Lotspeich (ll), who stressed the mutual inhibitory effect of these ions 
in tubular reabsorption. 
The relation of the serum sodium concentration and the rate of filtra- 
tion of potassium to the t/L values of these ions appears to be consistent. 
However, it must be emphasized that the experiments described in this report 
were of less than 3 hours duration. The assumption that these relationships 
will also hold in steady state experiments or in the presence of falling 
serum electrolyte concentrations is unjustified. Furthermore, it is clear that 
many other variable factors will depress the t/L Na and the t/L K in addition 
to those that have been described. It is common knowledge that the state of 
alkalosis can be accompanied by a sodium diuresis in the presence of a normal 
serum sodium concentration. Furthermore, Elkinton and Taffel (L) have clear- 
ly demonstrated that dehydration in the dog will effect a sharp increase in 
19 the serum sodium concentration associated with a rise in potassium excretion 
and the virtual absence of sodium in the urine. 
.Vesson, Anslow and Smith (15) strengthened the concept of the obliga- 
tory and the facultative reabsorption of water and sodium. The use of the 
t/L function parallels their concepts of a constant proximal tubular 
reabsorption of sodium and a varying distal reabsorption. They have supported 
the concept that the tubular reabsorption of sodium is functionally related 
to the filtration rate because an approximately constant fraction of the fil- 
tered sodium is reabsorbed by the proximal tubule and thin limb regardless 
of the filtration rate. It has not been possible to evaluate the investiga- 
tions described in this report in terras of their concept primarily because 
of the introduction of the variable factor of a massive NaCl infusion. By 
this means, the overall percentage of filtered sodium reabsorbed was con- 
sistently depressed below the $5% reabsorption of the proximal tubule and 
thin limb. The meaning of the added mechanism involved is obscure at the 
present time, furthermore, the role of the serum sodium concentration appears 
important in the regulaiio i of the reabsorption of filtered sodium. In justi- 
fication of the proposal that the serum sodium concentration regulates tubu- 
lar reabsorption, these investigations are complementary to the concepts ex- 
pressed by Gamble (5) in regard to the preservation of the normal total ionic 
level within the body. 
No explanation is forthcoming at the present time for the mechanism 
underlying these factors or for the mechanism involved in the activation of 
tubular secretion of potassium. Apparently the excretion of potassium by 
the kidney is controlled by a different mechanism than the excretion of 
sodium. 
IV. CONCLUSIONS 
A, The renal tubular reabsorption of sodium and potassium has been 
studied in 6 unanesthetized dogs in 28 experiments comprising 129 clearance 
periods. The serum concentration of the two ions was elevated progressively 
over wide ranges by continued intravenous infusion of solutions of the cor- 
responding chloride salts. 
B, The percentage of filtered sodium which is reabsorbed by the tubules 
is functionally related to the serum sodium concentration. 
C, The percentage of filtered potassium whiefc is reabsorbed by the 
tubules and the rate of excretion of potassium are closely related to the 
rate of filtration of potassium. 
D, The infusion of hypertonic sodium chloride depresses the fractional 
tubular reabsorption of potassium in excess of that ascribable to the simul- 
taneous incre-se of the potassium filtered load, 
E, The infusion of potassium chloride solution depresses the tubular 
reabsorption of sodium at normal serum sodium concentrations. 
F, The ingestion of potassium chloride prior to the infusion of this 
salt markedly augments the depression of tubular reabsorption of potassium 
ascribable to the increased potassium filtered load. Presumptive evidence 
indicates that tubular secretion of potassium was in part responsible for 
this apparent depression. 
20 G, The reabsorption of sodium is not limited by a tubular maximum 
H, The possibility is presented that a tubular maximum for potassium 
is concealed in our experiments by the simultaneous secretion of potassium 
by the renal tubules. 
I. During the Infusion of sodium chloride solution, the rise in serum 
sodium concentration is roughly paralleled by the rise in renal plasma 
flow and filtration rate. During tne .infusion of potassium chloride solu- 
tion, the rise in serum potassium concentration shows no such correlation. 
V. RECOMMENDATION 
Investigations should be carried out to determine the other factors 
which regulate the fraction of filtered sodium reabsorbed by the renal 
tubules. The mechanism of tubular secretion of potassium should be studied 
further. 
VI. BIBLIOGRAPHY 
1. Berliner, R, W* and T, J. Kennedy, Jr. **enal tubular secretion 
of potassium in the normal dog. Proc, Soc. Exper, Biol. & lied. 
62: 542, 1948. 
2. Brod, J. arxi J. H, Sirota. The renal clearance of endogenous 
creatinine in man. J. Clin. Investigation. ZJji 645, 1948. 
3. Bicker, S. S. Renal excretion of sodium and potassium in rats. 
J. Physiol. 10?• 8, 1948. 
4. Elkinton, J. R, and M, Taffel. Prolonged water deprivation in 
the dog, J. Clin. Investigation 21: 787, 1942. 
5. Gamble, J. L, Chemical anatomy, physiology and pathology of 
extracellular fluid. A Lecture Syllabus. Cambridge, Harvard 
University Press, 1947, chart 35-A. 
6. Harrison, H, E. A modification of the diphenylaxnine method for 
determination of inulin. Proc. Soc, Exper. Biol. & Med, 
A2: 1U» 1942. 
7. Harrison, H, S, and H, C. Harrison. The renal excretion of 
inorganic phosphate in relation to the action of vitamin D and 
parathyroid hormone. J. Clin. Investigation 20: 47, 1941. 
8. Lotspeich, W, D, Renal tubular reabsorption of inorganic sulfate 
in the normal dog. Am, J, Physiol. 151: 311, 1947* 
9. Mudge, G, H,, J. Foulks and A, Gilman, The renal excretion of 
potassium. Proc. Soc. Exper. Biol. & Med, 67: 545, 1948, 
10, Pitts, R. F. and R. S, Alexander. The renal reabsorptive mechanism 
for inorganic phosphate in normal and acidotic dogs, Am. J, Physiol. 
142: 648, 1944. 
21 11. Fitts, R. F, and W, D, Lotspeich. bicarbonate and the renal 
regulation of acid base balance. Am, J. Physiol. 147: 138, 
1946. 
12. Schwartz, B. P. K. Smith and A, W, tinkler. Renal excretion 
of sulfate. Am. J. Physiol. 137: 658, 1942. 
13. Stewart, J, D, and G. II, Rourke, Effects of large intravenous 
infusions on body fluid. Clin. Investigation 21: 197> 1942. 
14. Smith, H. W,, N, Finkelstein, L. Aliminosa, B, Crawford and 
M. Graber. The renal clearances of substituted hippuric acid 
derivatives and other aromatic acids in dog and man. J. Clin. 
Investigation 388, 1945. 
15. Wesson, L. G, Jr., u, P. Anslow, dr. and H, Smith. The excre- 
tion of strong electrolyte. Bull. New Xork Acad. 586, 
1948. 
16. Winkler, A. W, and P. K. Smith. Renal excretion of potassium 
salts. Am, J, Physiol. 138: 94, 1942, 
17. Wolf, A, V, regulation of water and some electrolytes in 
man, y/ith special reference to their relative retention and 
excretion. Am, J, Physiol. 148: 54, 1947. 
22