THE PRODUCTION OF CHRONIC SYSTEMC HYPERTENSION IK THE RAT 
WITH A SMALL ADJUSTABLE RENAL ARTERY CLAMP* 
by 
E, R, Munnell, Capt., M.C, and Dr. D. E, Gregg, 
Chief Research Physician 
from 
Medical Department Field Research Laboratory- 
Fort Knox, Kentucky 
2 September 1949 
*Sub-project under Study of Body Reactions and Requirements under Varied 
Environmental and Climatic Conditions. Approved 31 May 1%6. 
MDFRL Project No. 6~6/+-12-06-(3). Project No, 6-64-12-06-3) 
Sub-project MDFRL 06-3 
MEDEA 
2 September 1949 
ABSTRACT 
TOE PRODUCTION OF CHRONIC SYSTEMIC HYPERTENSION IN THE RAT 
WITH A SMALL ADJUSTABLE RENAL ARTERY CLAMP 
OBJECT 
An adequate method for the production of a persistent elevation of 
systemic blood pressure in the rat was desired. Several existing methods 
were tested, A small adjustable silver clamp, modeled after the larger 
Goldblatt clamp, was developed for application to and constriction of 
the renal arteries. 
RESULTS AND CONCLUSIONS 
Using published methods for inducing hypertension, only 15 per cent 
of the rats developed a persistent elevation of blood pressure. 
Bilateral application and adjustment of the renal artery clamp at one 
operation has caused in 10 of 11 rats a persistent elevation of blood 
pressure. The augmented blood pressure developed in 4-40 days and ranged 
from 160-220 mm. Hg, In rats operated upon with application and immediate 
removal of clamps (controls), pressures ranged from 100-140 mm. Hg. Eight 
of the 11 rats are alive and well 3-5 months after operation. These studies 
are being extended. 
RECOMMENDATIONS 
None, 
Submitted by: 
Edward R, Munnell, Capt., M.C, 
Donald E, Gregg, Chief Research Physician 
proved s 
RAY Qi MGGS (J ) 
Director of Research 
Approved: 
FREDERICK J. KNOBLAUCl 
Lt. Coi., r.c. 
Commanding THE PRODUCTION OF CHRONIC SYSTEMIC HYPERTENSION IN THE HAT 
'/ITH A SHALL ADJUSTABLE RENAL ARTERY CLAMP 
I. INTRODUCTIOt 
In connection with studios concerning the production of arterio- 
sclerosis in the coronary arteries, the need arose for an adequate method 
to induce chronic hypertension in the rat. Although numerous experimental 
procedures have been devised for the production of chronic hypertension 
in the rat, results have varied according to the method and the technique 
used for the determination of blood pressure. Published reports do not . 
indicate that permanent hypertension has been produced with the regularity 
necessary for undertaking a systematic study. Partial nephrectomy (l) has 
led to hypertension but the method has not been effective in the hands of 
Grollman and Williams (2). A constricting ligature has been used on one or 
both renal arteries or combined with a contralateral nephrectojry, and was 
reported to produce hypertension in 50 per cent of aniinals operated upon 
(3/. however, others have found this procedure unsatisfactory (2), or have 
noted its disadvantages (4). Wilson and Byrom (5) applied a small silver 
clip to the left renal artery with a resulting hypertension (140-250 mm, hg) 
lasting 5 dats to 46 weeks in 70 per cent of the animals, however, the 
distribution in time of the surviving rats was not indicated and the blood 
pressure was recorded under anesthesia. Application of constricting cotton 
tape to the poles of the kidneys in two stages 3 months apart, followed 3 
months later by unilateral nephrecto/qy (in those rats with a normal blood 
pressure), is reported to give a high percentage of animals with chronic 
hypertension (6). however, the duration of the hypertension is not known, 
Fibrocollagcnous perinephritis produced by foreign substances such as silk 
(2), collodion (?)* or rubber (4) caused a hypertension of variable duration 
and degree, Remington (8), using the cellophane perinephritis method, found 
that only 23 per cent of 1600 rats became chronically hypertensive. 
In the dog, chronic hypertension is induced with comparative ease and 
failures are unusual. Since so much of the successful experimental work on 
hypertension in the dog is based on the results of the application to the 
renal arteries of the Goldblatt clamp (9), it would be exceedingly helpful 
if a similar method could be standardized to give a high percentage of 
chronic hypertensive rats. Accordingly, the possibility of the development 
of an adjustable clamp for use on the renal arteries of the rat was explored 
experimentally, results are reported here, together with attempts to 
use some of the existing methods. 
II. EXP2RIMEWTAL 
A. Apparatus. Methods and Procedures 
•ihlte male and female rats of the V/istar and Sprague-Dawley strains 
were maintained on Purina Laboratory Chow and kept in separate cages in an 
air conditioned room. Each animal was anesthetized with sodium pentobarbital, 
4 mgm./lOO gm., administered intraperitoneally. 
1 Four existing methods for inducing hypertension were first tried. 
In each, the instruments and suture materials were sterilized in 70 per cent 
alcohol, hair in the region of operation was clipped and the skin prepared 
with either tincture merthiolate 1:1000 or tincture zephirin Is1000. Muscle 
and fascia were closed with 4-0 silk. Skin closure was made with Michel 
clips which were removed 7-10 days after operation. In the first method, 
a silver clip as described by V/ilson and Byrom (5) was applied to the right 
renal artery and, approximately one month later, the left kidney was either 
removed, wound with cellophane tape (10), or a cellophane capsule applied 
(ll). In the second method, the kidneys were delivered bilaterally through 
lumbar incisions and latex capsules applied to them (4)• In the third 
method, the poles of the right kidney were constricted and distorted with 
2 mm. wide cellophane tape as described by Grollraan (6) and modified by 
Ablondi (10). The left kidney was removed one week later. In the fourth 
method, constricting ligatures were placed on the renal arteries (3)* In 
some of these rats the ligatures were applied bilaterally at one operation; 
in others, one renal artery was constricted and 90 days later a constricting 
ligature was applied to the contralateral renal artery in those rats that 
did not develop an elevation of blood pressure. 
In the fifth method, a small adjustable silver clamp (Figure l), 
modeled after the larger Goldblatt clamp, was applied to the renal arteries. 
This measured 1.7 mm. in height, 1.65 mm* in length, and 1.5 mm. in width. 
The clamp was made of sheet silver 0.25 mm. thick (0.01") and nickel wire. 
A strip was rough cut to size for the casing (Figure 2, part l). The edges 
were rounded and shaped with a fine stone to exact size and formed with a 
carefully' machined punch die. On the top, a hole was centered, drilled, and 
tapped for the screw. Slots were cut for the removable plate 0.25 mm. ffom 
the ends. The screw (Figure 2, part 2) was made of nickel wire (0.85 mm. 
diameter) which was threaded (6 threads/ram.), and one end cut with a lathe and 
drilled to accommodate the movable plate. A 2-millimetar length was cut and 
slotted to take a small screw driver. It was then screwed into the casing. 
The movable compressing plate (Figure 2, part 3) was drilled and the hole 
counter-sunk. It was cut and shaped to size. All edges were rounded. The 
plate was then peened to the screw. A facing plate (Figure 2, part 4) of 
0.12 mm. silver was formed and bent to fit the moving plate. Finally, the 
removable bottom plate (Figure 2, part 5) was cut, shaped, and finished. 
Originally, somewhat larger clamps, 2 mm, in length, 1*5 if 
width, and 2 mm. in height were used. As indicated below, results 
this clamp wore not considered adequate, although they were better than 
those obtained with the previously published methods. 
The operative procedure for the application of the adjustable clarop 
was the sane as for the other methods except that instruments and suture 
material were autoclaved, the animal draped, and rubber gloves worn by the 
operator. The renal arteries were exposed through lumbar incisions. A 
clamp was applied at one operation to each renal artery after it had been 
cleared of connective tissue for a distance of 3-5 mm, about 1,0 men. from 
the aorta, The removable plate of the clamp was taken out and held with a 
pointed hemostatic forceps. With a curved, blunt-pointed iris forceps, 
modified to hold the clamp, the inverted clamp was slipped under and up 
around the artery. The removable plate was seated and aligned. The clamp 
was then rotated through 180 degrees to bring the screw into view. The screw 
was turned down to give complete occlusion and then turned back a definite 
2 FIG. I. DIMETRIC DRAWING TO SCALE OF THE ADJUSTABLE 
CLAMP WHICH MEASURES 1.7mm. IN HEIGHT| I.5mm 
IN WIDTH, AND 1.65mm. IN LENGTH. 
3 FIG. 2. ASSEMBLY DRAWING OF CLAMP IN FIG.l. DETAILS IN TEXT. 
4 amount with a small screw driver. Wound closure was performed as 
in the other experiments. 
The blood pressure of the rat was determined with the photocell- 
mi croamnieter apparatus of Kersten e£ (12), as modified in this labora- 
tory (13). With this modification approximately 76 per cent of the values 
fall within a maximal deviation of 1 10 mm, Hg from the systemic pressure 
simultaneously recorded in the carotid artery. Control pressures were taken 
on each rat prior to the operation for the production of hypertension. This 
varied from one to several weekly determinations. After operation, pressures 
were followed at weekly intervals except in the group with the adjustable 
clamp on the renal arteries in which pressures were recorded daily. Rats 
that developed pressures over 160 mm, Hg which lasted at least 4 weeks were 
arbitrarily designated as chronic hypertensives. 
B. Results 
'Vhile hypertension was produced by each of the previously pub- 
lished methods used, the percentage of rats with an elevated blood pressure 
was not large and no one method gave a high percentage. In a total of 83 
rats, 30 maintained a normal pressure for at least 8-40 weeks. Sixteen per 
cent developed a chronic elevation of blood pressure, and 8 per cent developed 
a hypertension but died in less than 4 weeks, giving a total of 24 per cent 
which showed a blood pressure elevation above 160 mra. Hg, Hypertension 
developed in 1-27 weeks. 
A somewhat larger adjustable silver clamp 12 nun. in length, 1,5 mm. 
in width, 2 mra. in height) than in Figure 1 was initially applied bilaterally 
to the renal arteries of 27 rats. A reproducible degree of constriction 
compatible with sustained hypertension was not found with this clamp, only 
52 per cent of the rats showing an elevated pressure which lasted from 1 to 
at least 20 weeks. 
The small adjustable clamps were first applied to both renal 
arteries of 5 rats and the compressing plate backed off from 1/2 to 1 turn. 
All the rats died with massive infarcts of both kidneys. The clamps were 
then applied to 11 rats and backed off 1-1/2 turns bilaterally. In 2 control 
animals the damps were applied and then removed. Table 1 is a summary of the 
data from these rats. The pressures in the control rats ranged from 100 to 140 
mm. Hg. Ten of the 11 rats developed hypertension in from 4 to 40 days. Eight 
of the 11 rats are alive and well 3 to 5 months after operation, with blood 
pressures in 7 of the rats ranging from 160 to 220 mm. Hg, Although the eighth 
rat is not considered to be in the hypertensive group, its pressure ranges 
between 150-160 mm, Hg which is well above the control range of 105-120 mm. Hg, 
Of the 3 rats that died, one died 7 days after operation with a blood pressure 
of 160 mm. Hg. The second rat developed a respiratory infection 7 weeks after 
the blood pressure elevation, with a consequent reduction in pressure and death 
with a normal blood non-protein nitrogen (NPN), The third rat developed 
diarrhea 12 weeks after elevation of blood pressure and died 1 week later with 
a blood NPN of 5# mgm. per cent. 
Figure 3 illustrate® the typical course of the blood pressure in 
a control rat. Figures k and 5 illustrate the typical course of the blood 
pressure after bilateral renal artery constriction in 2 rats. 
5 FIG. 3. GRAPH SHOWING BLOOD PRESSURE RANGE IN CONTROL RAT. 
DETAILS IN TEX'* , 
6 FIG. 4 GRAPH SHOWING EFFECT UPON BLOOD PRESSURE OF BILATERAL APPLICATION 
OF SMALL RENAL ARTERY CLAMPS 
7 FIG. 5. GRAPH SHOWING EFFECT UPON BLOOD PRESSURE OF 
BILATERAL APPLICATION OF SMALL RENAL ARTERY 
CLAMPS. 
8 A 
B 
c 
D 
E 
F 
RAT 
NO. 
WEIGHT gm. 
TIME ( DAYS) 
BP RANGE 
(mm. Hg) 
DURATION 
PRE - 
OP 
PRE - 
SENT 
UNTIL BP TO 
160 m m. Hg 
PRE-OP 
AFTER TIME 
COL. C 
HYPERTENSION 
WEEKS 
REMARKS 
350 
432 
105-110 
100-120 
— 
CONTROL-NO CLAMPS 
LIVING 13 WKS. 
4 0" 
290 
365 
112-120 
100-140 
CONTROL-NO CLAMPS 
LIVING (2 WKS. 
2 
370 
348 
8 
105 - L25 
160 - 210 
1 1 
DIED 12 WKS. POST OP. 
NPN 58. 
I 3 
350 
200 
1 7 
1 10-115 
160 - 200 
6 
DIED 8 1/2 WKS. POST OP. 
i 5 
345 
4 t 5 
1 1 
104 - 1 12 
160 - 220 
14 
LIVING. 
3 2 
420 
392 
1 6 
105 - 110 
165 - 194 
1 2 
LIVING. 
3 3 
3 35 
360 
4 0 
1 1 0 - 117 
160 - 200 
8 
LIVING. 
3 4 
395 
432 
105 - 120 
150 - 160 
— 
LIVING 14 WKS. 
3 5 
330 
347 
! 9 
M 0 - 120 
180 - 220 
It 
LIVING. 
3 8 
360 
326 
2 0 
103 - 120 
165 - 190 
1 1 
LIVING. 
3 9 
385 
385 
25 
103 - 118 
150 - 180 
LIVING. 
42 
3 1 C 
352 
3 1 
120-125 
160 - 180 
3 
LIVING. 
01ED (DIARRHEA) 1 WK. j 
4 4 
POST OP. 
pATS *iC. 36 AMO NO. 40 .CONTROL OPERATION, CLAMPS APPLIED AND IMMEDIATELY REMOVED. ALL 
•-HER RATS 0 CLAMPS APPLIED BILATERALLY AT ONE OPERATION. EACH BACKED OFF I - \/ 2 TURNS. 
TABLE I 
EFFECTS UPON BLOOD PRESSURE OF APPLICATION OF 
SMALL RENAL ARTERY CLAMPS 
9 >Vhile the results with the present adjustment of the clamps are 
encouraging, the optimum degree of constriction of the renal arteries must 
be determined by future experiments. 
in. SUMMARY AND CONCLUSION* 
Several of the reported methods for inducing persistent elevation of 
blood pressure in the rat have been used, Vith these, only 16 per cent of 
the animals developed a persistent hypertension. 
A small adjustable renal artery clamp is described which, when applied 
bilaterally at one operation, has caused a persistent elevation of blood 
pressure for months in 10 of 11 rats. These studies are beinr extended. 
IV. ICSCOlflalSNDATIONS 
None. 
V. BIBLIOGRAPHY 
1. Chanutin, A. and i£. B, Ferris, iacperimental renal insuffi- 
ciency produced by partial nephrectony. Arch. Int. 767, 
1932. 
2. Grollman, A, and J. R, //iI llama, Jr,: Experimental chronic hyper 
tension in the rat. Am, J, &ed. Science 201: 73, 1942. 
3. Kenpf, G. F* and I. H, Page: Production of experimental hyper- 
tension and the indirect determination of systolic arterial pressure 
in rats. J. Lab. & Clin. Med. 2%: 1192, 1942. 
V. Abraias, M, and S, Sobin: Latex rubber capsule for producing hyper- 
tension in rats by perinephritis, Proc, Soc, Exp, Biol, & Med. 
412, 1947. 
5. Wilson, C. and F. B. Byrom: The vicious circle in chronic Bright’s 
disease. Sxperiiaental evidence from the hypertensive rat. 
J. Med. 10: 65, 1941. 
6. Gb*ollrnan, A*: A simplified procedure for inducing chronic renal 
hypertension in the mammal, Froc, Soc, Exp. Biol, &. Med, 
2L: 102, 1944. 
7. Eafce, E, >/,, E• S, Patton, and E, Ogden: Effect of pregnancy on 
experimental hypertension, with observations on effects of deci- 
duomas. Am, J. Obst. & Gynec. 41: 53* 1941. 
FOOT authors wish to express their indebtedness to Sgt, D, R, Ball 
(30th Ord. lank Haint. Co,), H, Schuchmann, and R, A, Hofmann for their 
aid in making the clamps. Acknowledgment is made of technical assistance by 
B, C, Patterson, 
10 8, Remington, J, V7,, G, F. Cartland, V, A, Drill and W, W, Swingles 
Purification and bioassay of tissue extracts capable of lowering 
the blood pressure of hypertensive rats, Am, J. Physiol, 
2kOf 62?, 1%4. 
9. Goldblatt, H#, J, Lynch, R. F, Hanzal and W, W# Sunmerville j 
Studies on experimental hypertension. I. Production of persistent 
elevation of systolic blood pressure by neans of renal ischemia. 
J. Kxper. Led. 347, 1934. 
ID. Ablondi, F,: Personal cocanunication, 1943* 
11. Page, I. H.i A method for producing hypertension by cellophane. 
Science SJi 273, 1939. 
12* Kersten, H., w, G, Brosene, F, Ablondi and I. SubbaRow: A neiv 
method for the indirect measurement of blood pressure in the rat. 
J. Lab. & Clin. lied. 1090, 1947. 
13o Munnell. Edward R, and D, E, Oregg: To be published. 
11