Within the last year, evidence (1-4) has accumulated to show that the kidney secretes a hormone which is a prime regulator of aldosterone secretion. The renal origin of an aldosteronestimulating hormone (ASH) has been demonstrated following acute blood loss (1-3), during chronic thoracic caval constriction (4), and during chronic Na depletion (4). Nephrectomizedhypophysectomized dogs failed to respond to acute hemorrhage with an increase in aldosterone secretion, and acute bilateral nephrectomy of hypophysectomized caval and hypophysectomized Nadepleted dogs resulted in a marked drop in aldosterone secretion. Furthermore, crude saline extracts of kidney produced a striking increase in aldosterone secretion (1-5). In malignant experimental renal hypertension, hyperaldosteronism was consistently present (6). These findings and the reports that renin preparations (6) and synthetic angiotensin II (6-8) increase the rate of aldosterone production suggest the possibility that ASH is renin.The present experiments were undertaken to determine the chemical nature of this ASH by fractionation of crude kidney extracts for aldosterone-stimulating and pressor activity. The renin content of kidneys from dogs with thoracic caval constriction and secondary hyperaldosteronism and from normal dogs has been compared.

Since Ruyter (1) first described epithelioid cells in the preglomerular arteriole of the kidney, many attempts have been made to elucidate the function of these apparently endocrine "juxtaglomerular cells. ''1 Goormaghtigh (2), from his extensive observations in hypertension and related conditions, postulated that they were probably the source of the vasopressor substance, renin. Among others, Dunihue (3, 4) subscribed to this theory, and his more recent investigations have revealed a relationship between juxtaglomerular cells and the adrenal glands (5). In adrenalectomized animals he found an abnormal increase of secretory granules which could be prevented or reversed by administration of desoxycorticosterone acetate (])CA) (6). A similar increase in granules has also been described by McManus (7) in kidneys from cases of Addison's disease in man. Since DCA is the salt-retaining hormone, these findings suggested to us that the effect of adrenal insufficiency on juxtaglomerular cells might be due primarily to a disturbance in sodium metabolism and that this effect could perhaps be produced by dietary means alone. The current clinical use of diets low in sodium for the treatment of hypertension further stimulated our interest in this possibility.In a preliminary experiment, we were able to demonstrate in the rat, that restriction of dietary sodium chloride for a period of 2 weeks to 1 month caused a striking increase in the numbers of granules in the juxtaglomerular cells. A further series of experiments was then designed to confirm these observations and to determine the effect of variations in the level of dietary sodium chloride with or without DCA administration.

Hypersecretion of aldosterone occurred at the onset of signs of congestive heart failure in a large series of dogs with a large infrarenal aortic-caval fistula. There was evidence of right heart failure in all animals and in four of the dogs râles or frank pulmonary edema was present. Marked sodium retention and ascites or edema were consistent findings and in the majority of the animals central venous pressure was elevated. Hypophysectomy was followed by a striking fall in both aldosterone and corticosterone secretion but in several animals hypersecretion of aldosterone was evident in the absence of the anterior pituitary. Subsequent acute bilateral nephrectomy of these hypophysectomized dogs resulted in a marked drop of aldosterone secretion to a very low level, and a precipitous fall in arterial pressure frequently occurred. An intravenous infusion of a saline extract of each animal's kidneys produced a striking elevation in aldosterone output; corticosterone secretion and arterial pressure increased consistently. The kidneys of these dogs with heart failure secondary to an A-V fistula frequently showed hypergranulation and hyperplasia of the juxtaglomerular cells. The present findings suggest that the increased rate of aldosterone secretion was mediated by the renin-angiotensin system. Measurements of arterial pressure and renal hemodynamic function demonstrated a fall of mean renal arterial pressure, glomerular filtration rate, and renal plasma flow, whereas arterial pulse pressure above the fistula and presumably in the kidneys was increased. The data suggest that decreased pulse pressure is unnecessary for activation of the renal mechanism leading to hyperaldosteronism.

Canine antisera to rabbit and hog renin were coupled to several fluorescein dyes. The antiserum was immunologically adsorbed once each with rabbit-liver and with bone-marrow powder, thereby removing excess dye and eliminating nonspecific staining. Mounted frozen-dried sections of kidneys from sodium- deficient rabbits (in which hyperplasia and hypergranulation of juxtaglomerular [JG] cells were present), from control rabbits, from a sodium-deficient dog, and from sodium-deficient rats were treated with the adsorbed labeled antiserum. Ultraviolet microscopy (direct technique) revealed an intense yel low-green fluorescence sharply limited to the granules of the juxtagloinerular cells in all sections studied from kidneys of rabbit and dog. JG granules in rats did not fluoresce, an observation in accord with the species spe cificity of renin. The indirect ("sandwich") method was also employed (with adsorbed, labeled, rabbit antiserum to canine globulin), and although slight staining of gloinerular epithelium resulted, that in the JG granules was far more intense. In our hands, the faint glornerular staining was not blocked by prior treatment with unlabeled renin. Staining of JG granules in any kidney paralleled the intensity of JG granulation by light microscopy and the amount of extractable renin in the same kidney. JG-granule staining (direct and indirect techniques) was blocked by neutralization of the antirenin with renin. Heterogenous anti sera (to insulin; to human gamma globulin) failed to stain. Other rabbit tissues (heart, lung, liver) similarly treated with labeled antirenin never stained. If this work can be repeated with immunologically pure renin, the evidence presented here, together with previously published studies from this and other laboratories, will establish beyond any reasonable doubt that the source of renin in the kidney is the juxtaglomerular cell, as postulated first by Goormagh tigh nearly a quarter of a century ago.