STUDIES ON EXPERIMENTAL HYPERTENSION : XIV. THE EFFECT OF INTERMITTENT RENAL ARTERIAL OCCLUSION ON THE BLOOD PRESSURE OF THE DOG

By means of a silver chain attached to a silver ring around the main renal artery, intermittent renal arterial occlusion, up to 30 minutes daily, was practiced for as long as 5 months in unilaterally nephrectomized dogs. This did not result in the development of persistently elevated blood pressure. Persistent moderate constriction of the renal artery of such animals by a silver clamp, after intermittent temporary occlusion had failed to affect the blood pressure, produced the usual rise of blood pressure, without accompanying significant impairment of renal excretory function. When the renal artery accidentally became persistently constricted to a great degree, or actually occluded, or if occlusion was deliberately produced by continuous pulling of the chain, hypertension and renal insufficiency (the malignant phase) quickly developed. The results do not lend support to the view that brief daily periods of renal ischemia from intrarenal vasospasm, or from any other cause, can produce persistent hypertension of renal origin.     

STUDIES ON THE RENAL ARTERIAL BLOOD PRESSURE AND THE METABOLISM OF KIDNEY TISSUE IN EXPERIMENTAL HYPERTENSION

1. In the hypertension which accompanies constriction of the renal arteries, there is no constant relationship between the height of the general systemic arterial pressure and the pressure in the renal artery distal to the point of constriction. The hypertension may persist even though the renal arterial pressure returns to or almost to the control level. 2. Studies on the renal blood flow and oxygen consumption following subtotal nephrectomy were abandoned because of inability to produce hypertension in dogs by this method. It is suggested that the mechanism of the hypertension following renal arterial constriction (dogs) and that following subtotal nephrectomy (rats) may not be the same in the two instances. 3. Studies on isolated renal cortical tissue of dogs and of rabbits following renal arterial constriction and subtotal nephrectomy showed that there is not necessarily a diminution in the capacity of the tissues of hypertensive animals to use oxygen.     

STUDIES ON EXPERIMENTAL HYPERTENSION : II. THE EFFECT OF RESECTION OF SPLANCHNIC NERVES ON EXPERIMENTAL RENAL HYPERTENSION

Excision of the thoracic portion of the splanchnic nerves and the lower four dorsal sympathetic ganglia on both sides failed to prevent the development of persistent hypertension which, in dogs, follows the production of renal ischemia by partial clamping of the renal arteries (1). In dogs with this type of experimental renal hypertension existent for varying lengths of time (up to about 4 years), excision of the splanchnic nerves and the lower four dorsal sympathetic ganglia failed to effect any degree of permanent lowering of the blood pressure. For the dog, at least, these results tend to minimize the importance of the splanchnic vasomotor mechanism in the pathogenesis of renal hypertension. This is in agreement with the conclusions of Prinzmetal and Wilson (6) and of Pickering (7) about the part played by the vasomotor system in human hypertension. It is also in agreement with the work of Page (8), and of Collins (9), who showed that in dogs excision of the extrinsic renal nerves alone does not prevent experimental hypertension due to renal ischemia. Although the results of this investigation fail to give experimental support for the operation that is being practised on human beings with hypertension, yet they do not necessarily controvert the reports of beneficial effects in some cases of human hypertension. Further study of the effects on man is necessary before the results of this operation can be adequately evaluated.     

STUDIES ON EXPERIMENTAL HYPERTENSION : I. THE PRODUCTION OF PERSISTENT ELEVATION OF SYSTOLIC BLOOD PRESSURE BY MEANS OF RENAL ISCHEMIA

These experiments indicate that, in dogs at least, ischemia localized to the kidneys is a sufficient condition for the production of persistently elevated systolic blood pressure. When the constriction of both main renal arteries is made only moderately severe in the beginning, the elevation of systolic blood pressure is unaccompanied by signs of materially decreased renal function. In this respect the hypertension in these animals resembles the hypertension which is associated with so called benign nephrosclerosis in man. Subsequent increase of the constriction of the main renal arteries does not materially damage renal function, probably because of adequate development of accessory circulation. More delicate methods for detecting a change may yet prove that some damage does occur. Almost complete constriction of both main renal arteries, from the beginning, results in great elevation of systolic blood pressure which is accompanied by severe disturbance of renal function and uremia. This resembles the type of hypertension which is associated with so called malignant nephrosclerosis, in the sense of Fahr (17). In several of the animals with persistent elevation of systolic blood pressure, anatomical changes were observed in the glomeruli, vessels and parenchyma of the kidneys which are most probably directly referable to the ischemia. It is hoped that these investigations will afford a means of studying the pathogenesis of hypertension that is associated with renal vascular disease.     

EXPERIMENTAL HYPERTENSION : THE EFFECTS OF UNILATERAL RENAL ISCHEMIA COMBINED WITH INTESTINAL ISCHEMIA ON THE ARTERIAL BLOOD PRESSURE

Unilateral renal ischemia superimposed upon intestinal ischemia has resulted in a prolonged elevation in the arterial blood pressure in a high percentage of the animals which were studied.     

THE EFFECT OF HIGH PROTEIN DIETS ON EXPERIMENTAL RENAL HYPERTENSION

The effect of high and low protein diets were studied on fourteen dogs in twenty-four different experiments. In only two of these animals, both with moderate renal excretory failure, was a reversible rise in blood pressure elicited by a high protein diet. The possible mechanisms involved in meeting an increased excretory load are discussed.     

OBSERVATIONS ON THE PATHOLOGICAL CHANGES FOLLOWING EXPERIMENTAL HYPERTENSION PRODUCED BY CONSTRICTION OF THE RENAL ARTERY

The clinical histories and pathological findings of six animals dying within a few days following bilateral constriction of the renal arteries have been presented. No explanation for the rise in blood pressure was found. The clinical histories and pathological findings of twelve animals with a sustained hypertension have been considered together with the detailed account of one of these in which a marked degree of arterial disease was found. It has been suggested from the study of this group that, though no cause for the initiation of the hypertension was found, the induced arterial disease might account for its maintenance.     

STUDIES ON EXPERIMENTAL HYPERTENSION : VII. THE PRODUCTION OF THE MALIGNANT PHASE OF HYPERTENSION

The production of the acute malignant phase of experimental hypertension has been accomplished in seventeen dogs. The method used to produce this type of hypertension was the same as for the benign type (4), namely, constriction of the main renal arteries, or the equivalent, constriction of the aorta above the origin of both main renal arteries, but the constriction was especially severe. The malignant phase in the animals was characterized by hypertension, terminal renal insufficiency and the development of petechiae and larger hemorrhages in many internal organs, especially the alimentary tract. These were due to dissecting hemorrhage through, or rupture of, the wall of severely hyalinized or necrotic arterioles, or rupture of capillaries. Hyalinization and necrosis of arterioles were more severe and more widespread in animals that had a period of benign hypertension before the onset of renal insufficiency. In animals with a previous long period of benign hypertension, thickening of the media also occurred in arterioles, with or without hyalinized intima. Elevation of blood pressure (mechanical factor) and renal insufficiency (humoral factor) are at least two of the necessary conditions for the development of the necrotic arterioles and hemorrhages. Necrotic arterioles and hemorrhages have not yet been observed in animals that have had very high blood pressure for years without renal insufficiency, nor in animals with azotemia, due to removal of both kidneys, but without hypertension. Hyalinized retinal arterioles have been observed in dogs with persistent hypertension and with moderate or no disturbance of renal function. That ischemia is not the cause of the necrosis of the arterioles is shown by their absence from the ischemic kidneys of the dogs and their widespread presence in other organs that were not ischemic. These experiments show that the necrotic arterioles and hemorrhages are secondary to and not the primary cause of the malignant phase of hypertension.     

PRODUCTION OF ANTIRENIN TO HOMOLOGOUS RENIN AND ITS EFFECT ON EXPERIMENTAL RENAL HYPERTENSION

1. Procedures are described for the extraction and partial purification of dog renin, on a large scale, as well as for the acetylation of rat, rabbit, and dog renin. 2. Untreated homologous renin was not antigenic in rat, rabbit, or dog, but the acetylation of homologous renin made it antigenic. 3. Immunization of rats, rabbits, and dogs, with acetylated rat, rabbit, and dog renin, respectively, resulted in each case in the development of anti-renin to the homologous, untreated, as well as to the acetylated renin. 4. The progressive development of antirenin as a result of repeated, subcutaneous injections of acetylated dog renin, in a dog with experimental renal hypertension for more than 6 years, was accompanied by a correspondingly progressive fall of the mean arterial blood pressure to the prehypertensive level. This points up the important part played by the renin-angiotensin mechanism in the maintenance of the hypertension, even in the chronic phase of experimental renal hypertension.     

STUDIES ON EXPERIMENTAL HYPERTENSION : XIX. THE PRODUCTION OF PERSISTENT HYPERTENSION IN SHEEP AND GOATS

Persistent hypertension has been produced in the goat and sheep by constriction of the main renal arteries. The presence or absence of accompanying uremia depends upon the degree of constriction of the renal arteries. In both sheep and goat, constriction of one main renal artery also caused elevation of the blood pressure which tended to persist longer than in the dog. Excision of the one kidney with main renal artery constricted resulted in a prompt (24 hours) return of the blood pressure to normal. In the animals with hypertension of long duration but without renal excretory insufficiency, (the "benign" phase) no significant arterio- or arteriolosclerosis developed as a result of the hypertension alone. In the animals that had both hypertension and renal excretory insufficiency, (the "malignant" phase) the typical terminal arteriolar lesions developed in many organs. These lesions consisted of necrosis and fibrinoid degeneration of arterioles and necrotizing arteriolitis which should not be confused with arteriolosclerosis. The same humoral mechanism which is responsible for experimental renal hypertension in the dog and other animals also obtains in the pathogenesis of experimental renal hypertension in the sheep and goat.     

STUDIES ON EXPERIMENTAL HYPERTENSION : III. THE PRODUCTION OF PERSISTENT HYPERTENSION IN MONKEYS (MACAQUE) BY RENAL ISCHEMIA

Persistent elevation of systolic and diastolic blood pressure due to renal ischemia has been produced in monkeys (macaque) by the same method previously used for this purpose in dogs.     

STUDIES ON EXPERIMENTAL HYPERTENSION : XX. THE BIOASSAY OF RENIN

A simple, rapid method for the bioassay of renin has been presented. Reliable and consistent results are obtained by this method whereby an arbitrary dog unit of renin has been established. The response of normal unanesthetized dogs to renin is independent of the body weight of dogs weighing between 10 and 25 kilos. An estimate of potency of renin per kilo of body weight of the test animals is therefore not only unnecessary but misleading. A dog unit of renin has been defined as that amount which raises the blood pressure at least 30 and not more than 35 mm. Hg within 3 minutes in at least three unanesthetized dogs. The potency is expressed as dog units of renin per cubic centimeter. The determination of the amount of renal substance represented by a cubic centimeter of extract and the number of dog units per cubic centimeter give an estimate of the yield of renin which can be expressed as dog units of renin per gram of original renal tissue. By determination of the number of dog units per cubic centimeter and the amount of nitrogen in milligrams per cubic centimeter in any renal extract the purity of the renin can be determined and expressed as dog units of renin per milligram N. The establishment of a standard method for the bioassay of renin is considered highly desirable and the method outlined in this paper is suggested for this purpose.     

STUDIES ON EXPERIMENTAL HYPERTENSION : XXI. THE PURIFICATION OF RENIN

1. Extraction of finely ground fresh hog kidney with distilled water adjusted to pH 7.8 with sodium hydroxide, followed by successive treatment, as described, with trichloroacetic acid and acetone, gives renin in good yield of a purity suitable for physiological studies and a good starting material for further purification. It contains 15 dog units per mg. N. 2. Further successive purification of this material with ethyl alcohol and ammonium sulfate gives a preparation containing 130 dog units per mg. N. The purest preparation hitherto reported (15) contained 16.0 to 20.8 units per mg. N. Preliminary Tiselius electrophoresis studies suggest homogeneity, but further studies to establish purity are in progress. 3. The properties of the most purified renin indicate that it is a protein. Its chemical and physiological properties correspond to those of the material in crude renal extract which induces an elevation of blood pressure when it is injected intravenously.     

EFFECT OF VARIOUS AGENTS ON THE BLOOD FLOW THROUGH THE CORONARY ARTERIES AND VEINS

The results obtained show that adrenalin, transfusion with salt solution, and the inhalation of tobacco smoke caused an increased circulation in the coronary vessels. Amyl nitrite and nitroglycerin produce the opposite effect. Digitalis, strophanthus, caffeine, and theobromine give no change in the velocity of circulation. We can conclude from the results that the blood pressure is the main element which influences coronary circulation, while the other factors play only a minor part in its variations.     

STUDIES ON THE BLOOD CYTOLOGY OF THE RABBIT : IX. BLOOD PLATELET COUNTS ON HEALTHY MALE RABBITS

1. Repeated platelet counts, 991 in number, were made on 148 adult male rabbits of various breeds and types which were specifically selected on the basis of physical fitness and continued freedom from disease. The observations extended over a 2½ year period (1929–32). 2. A unimodal, peaked, moderately asymmetrical distribution curve was obtained and an analysis of the results gave the following values: the mean, 532,645 platelets per c.mm.; the median, 520,604 per c.mm.; the mode, 503,962 platelets per c.mm. respectively. 3. The extent of the variation among the counts is shown by the standard deviation of 124,960. High platelet counts were found to occur more frequently than low counts, a result that is reflected in a significant skew to the right in the frequency curve. 4. It was calculated that in healthy male rabbits a platelet count of less than 220,000 or more than 845,000 per c.mm. should be considered abnormal.     

STUDIES ON EXPERIMENTAL HYPERTENSION : X. THE OXYGEN CONSUMPTION OF THE ISCHEMIC KIDNEY

The consumption of oxygen by slices of renal tissue of the rabbit was studied by means of the Warburg manometric method. The ischemic kidney of the rabbit shows a definite diminution of oxygen consumption, compared with the normal kidney.