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The physicochemical properties of renin substrate in plasma from normal estrogen-treated and nephrectomized male rats were determined. The molecular radii molecular weights net charge and isoelectric points of substrates from 5 normal rats 5 rats 24 hours postnephrectomy and 5 rats 24 hours after intravenous injection of 100 mcg ethinyl estradiol were determined on polyacrylamide gels by the Rodbard and Chrambach technique. Plasma angiotensin 1 liberated by an excess of renin and measured by radioimmunoassay was 1200 ng/ml in normal rat 2300 ng/ml in estrogen-treated rat and 8000 ng/ml in binephrectomized rat. The 3 substrates revealed the same relative mobility. Their molecular radii were identical (r=2.23 mmc) and sizes (molecular weight=37200-40800) and isoelectric points (pI=4.79-4.83) were similar. It was concluded the estrogen treatment and binephrectomy increase the amount of available plasma renin substrate but do not modify its physicochemical properties.

Using a histochemical method, moderately strong glucose-6-phosphate dehydrogenase activity can be demonstrated in the macula densa of the distal tubules in the normal rat kidney. In rats rendered hypertensive by overdosage with cortexone (DOC) and saline, this enzymatic activity was found to decrease almost to zero within 4 weeks. This change was more marked in unilaterally nephrectomized animals than in intact rats. Measured by bioassay, the renin content of kidney extracts from the same animals was found to decrease simultaneously with the loss of enzymatic activity in the macula cells. The reverse effect, a marked increase in activity of the macula densa, was obtained in adrenalectomized animals. It is suggested that both the macula densa cells and the juxtaglomerular apparatus are parts of a system which respond similarly to changes in sodium balance and which may be related to the formation of renin.

Renin infusion produced initial increase in blood pressure and peripheral resistance. As infusion continued, blood pressure returned to base-line levels, but peripheral resistance remained slightly elevated. Noradrenaline infusion in the dog did not produce sustained hypertension, but the peripheral resistance remained elevated. Repeated renin injections finally produced no change of blood pressure or peripheral resistance. At this time the animal was nonresponsive to angiotensin. Return of blood pressure to base-line levels despite continued infusion of renin was felt to represent both a ‘cardiovascular failure of response’ and a more specific blockade of angiotensin response.

Free water clearance (CHH2O) was studied in five normal subjects and in a patient with diabetes insipidus before and during the infusion of angiotensin II (Ciba), .2 µg/min. With angiotensin, CHH2O fell markedly, with only small changes in urinary osmolality both in the normal subjects and in the patient with diabetes insipidus. The fall in CHH2O was accompanied by a fall in UNaV, effective renal plasma flow (ERPF), and glomerular filtration rate (GFR). A physiological dose of Pitressin (25 mU/hr) given after the angiotensin, abolished CHH2O and markedly increased urinary osmolality while UNaV, ERPF, and GFR returned toward normal. The results may be best explained as a direct effect of angiotensin on renal hemodynamics, to decrease filtered sodium and water. Reabsorption of an increased fraction of filtered sodium and water by the proximal tubule would limit the amount reaching the diluting segment of the nephron and excreted in the urine. A possible role for angiotensin in the impaired water excretion of certain disease states, such as Addison's disease and congestive heart failure was suggested.

Angiotensin blood levels were measured in anesthetized dogs under different experimental conditions. In hemorrhagic hypotension, a marked and progressive increase in angiotensin blood levels was detected. No increase was found when a similar reduction in renal perfusion pressure was elicited by constriction of the aorta above the renal arteries. A high dose of norepinephrine infused simultaneously with the constriction of the aorta produced a significant increase in angiotensin blood levels which was lower than the one detected after hemorrhage. A potentiation of the effect of dog renin injections on angiotensin blood levels by bleeding was shown. It is concluded that the rise in angiotensin blood levels after hemorrhage is not solely due to a decreased renal perfusion pressure. Other possibilities are discussed.

The separation of angiotensin I and angiotensin II by paper chromatography using an acid NaCl solution is described. When the pressor material recovered from the blood of dogs infused with renin was analyzed by this method, significant quantities of angiotensin I as well as angiotensin II were found in those infused at rates above 1 Goldblatt U/min. At infusion rates below 1 U/min, only angiotensin II was present. In each of six dogs with malignant experimental renal hypertension, significant increases in circulating pressor material were found 48 hr or more after renal artery constriction. Analysis of the material recovered from the blood of five of these dogs revealed only angiotensin II in four instances, and a mixture of angiotensin I and II in one instance.

Renal vascular responsiveness to angiotensin, epinephrine, norepinephrine, and histamine was investigated before and after endotoxin shock in 25 anesthetized dogs. Drugs were injected into the renal artery inflow tubing in constant-flow, isolated kidney preparations. Mean renal vascular responses were compared for both peak elevation of renal artery pressure (RAP) and area under the RAP curve. In situ kidney preparations in which angiotensin and norepinephrine were infused intravenously after endotoxin were utilized in several experiments. Renal blood flow (RBF) and the dog's arterial blood pressure (ABP) were measured in both groups. Renal vascular responsiveness to angiotensin was virtually abolished within 1 hr after endotoxin. The RAP elevation produced by epinephrine and the decreased RAP following histamine injections were not significantly altered. In the in situ kidney studies, angiotensin was initially effective in elevating ABP after endotoxin, but RBF was further depressed; by approximately 1 hr after endotoxin, angiotensin infusion was ineffective. Norepinephrine infusion maintained the animal's ABP at a normotensive level and did not seriously reduce RBF.

Studies were designed to determine parameters of force and velocity derived from isolated cardiac muscle mechanics which would permit comparison with related performance characteristics in the intact ventricle. In the papillary muscle, for a wide range of resting muscle lengths, tension developed isometrically (Po) was found a linear function of initial muscle length and proportional to the extent of isotonic shortening (δL). Length-tension curves obtained isotonically were virtually identical to those obtained isometrically. In the intact heart stroke volume is a function of δL. Ventricular end-diastolic pressure is a function of resting muscle length. As increments of resting muscle length increased δL, increasing ventricular end-diastolic pressure augmented stroke volume. Increasing the load carried by the muscle (afterload) at a given resting muscle length increased work performed by the papillary muscle. Similarly, increasing aortic pressure increased stroke work for a given ventricular end-diastolic pressure in the intact heart. In the papillary muscle time to maximal δL was an inverse function of maximal velocity of shortening (Vmax), but independent of both Lr and afterload. The inverse relation of time to max δL and Vmax were shown for norepinephrine and frequency. In the intact heart time to peak ventricular pressure, was found to be largely independent of ventricular end-diastolic and aortic pressures and inversely related to the inotropic state of the myocardium. Contractility of the papillary muscle strictly defined by Vmax and Po, was thus characterized by time to maximal δL, as well as δL. Contractility of the ventricle at a given ventricular end-diastolic pressure could then be defined by stroke volume and peak pressure time, which are indices of force and velocity.

The pressor effect of series of subcutaneous injections of hog renin was studied in the dog, as well as the modification of the pressor effects of renin by reserpine, hydralazine ( l-hydrazinophthalazine) and hexamethonium. In 22 of 27 experiments, short series of subcutaneous renin injections (1–37 days) in doses of 550–1800 cat units/day were repeatedly followed by moderate elevations of systolic and diastolic blood pressure, whereas control injections of saline, ACTH or extracts of liver were without effect on the blood pressure. In a number of instances, but not in all, a definite increase in plasma renin could be demonstrated during the pressor effect of renin. The pressor effect of subcutaneous renin was still observed during oral administration of reserpine (0.25 mg/day) and hexamethonium (250–500 mg/day) but was often absent during the administration of hydralazine (25 mg/day). The pressor response to intravenous renin was increased in animals receiving reserpine and hexamethonium and decreased after hydralazine. In vitro experiments with these three drugs failed to indicate any significant effect on the formation or destruction of hypertensin.

The effects were investigated in rats of unilateral renal ischemia, adrenalectomy and varying doses of cortexone on the development of hypertension and on the content of pressor substances in the kidney. Adrenalectomy prevented the hypertension which follows unilateral clamping of the renal artery when a life maintaining dose of 0.1 mg cortexone acetate was injected daily. However, administration of 75 mg cortexone in the form of implants restored but did not enhance the characteristic hypertensive response to renal ischemia. The characteristic distribution of renal pressor material, being normal in the clamped and diminished in the contralateral kidney, was no longer observed after adrenalectomy when only small doses of cortexone were given but was still evident when excess cortexone was given. Overdosage with cortexone without clamping a renal artery led only to a moderate reduction of pressor material in both kidneys while in animals with unilateral renal ischemia the pressor material (renin?) in the contralateral kidney disappeared completely. Clamping the renal artery prevented the diminution of pressor material in the ipsilateral kidney which otherwise occurs under overdosage with cortexone in the normal animal.

The accuracy of predictions of myocardial blood flow based on Rb86 clearance rates was determined in dogs receiving vasoactive drugs or subjected to hypoxemia or hypercapnia. In controls, the highest rate of coronary blood flow was 16.5 ml/g myocardium per 10 min. Flow could be predicted from clearance (tissue Rb86 uptake/arterial blood Rb86 concentration) with a mean error of 7.8% in this group. With hypoxemia estimates of flow averaged 13.8% too low when arterial blood was from 50 to 75% saturated with oxygen, and were more unreliable at lower values. Carbon dioxide tension had no effect in the range from 20 to 60 mm Hg, but at higher levels estimates of flow were frequently much too low. Reserpine slowed the pulse and resulted in predicted rates of flow which averaged 13.7% below actual rates. Angiotensin, l-norepinephrine, dipyridamole, and digitoxin had no significant effect on the prediction of flow from clearance in the range of flow observed in controls. Thus Rb86 clearance is a valid index of coronary flow in the range of CO2 tension, arterial oxygen saturation, and drug effects commonly observed.

In a study of the renin-angiotensinogen interaction, under various conditions of time, temperature and concentration of renin and angiotensinogen, an indirect method for the quantitative determination of renin in the kidneys and of angiotensinogen in the serum of nine species was developed. This method involves the bioassay of the angiotensin formed as a result of the incubation in vitro of purified renal extracts with homologous serum or plasma. Renin and angiotensinogen, at the concentrations of the latter existing in the serum of the various species, were both found to be rate-determining in the process of angiotensin formation. There were striking differences in the concentration of renin in normal kidneys of the various species, with rabbit kidney having more than 70 times as much renin as human kidney. A pronounced increase of renin was found in the ischemic kidney of dogs with experimental renal hypertension. An exceptionally high concentration of angiotensinogen was present in normal human serum compared to that of the eight other species investigated. The results of the previous and present determinations of the renin concentration in the kidneys of various species differ considerably because the former method depended upon a heterologous renin-angiotensinogen reaction, in vivo, while the present evaluation is based on a homologous renin-angiotensinogen reaction in vitro.

In rats treated with ganglion-blocking agents, potentiation of the pressor response to renin appears from 4 to 24 hr after bilateral nephrectomy has been performed, but the response to norepinephrine and angiotensin remains unchanged. Further studies support the theory that there is an activator or an inhibitor which influences the renin-angiotensinogen reaction. Production or storage of such a substance seems to be in the renal tissue.

An experimental nephrotic syndrome was produced in rats by aminonucleoside administration. Unlike previous results in animals given excess mineralocorticoid, aminonucleoside did not reduce the renin content of the kidney; did not cause an increased sensitivity to single or repeated doses of renin, whether renin was given from the beginning of the experiment or 2 days before edema formation; and did not cause hypertension. The severity of the nephrotic syndrome was augmented by a high-salt diet. The syndrome could be produced in adrenalectomized animals on maintenance doses of desoxycorticosterone acetate, suggesting that the hyperaldosteronism of aminonucleoside nephrosis is not the cause of the observed edema and ascites. Sharp distinctions can be drawn between the mechanisms of edema formation in experimental nephrosis and those of the ‘eclampsia-like’ syndrome.