Inhibition of sodium transport in isolated renal tissue by angiotensin

Effects of salt loading and haemodilution on the responses of perfused cat kidneys to angiotensin

1. Effects of single intra-arterial injections (0.1-1.0 mug) of angiotensin II have been observed on cat kidneys perfused with heparinized blood from heart-lung circuits.2. Angiotensin II always caused an abrupt decrease in renal plasma flow (R.P.F.) which reached maximum in 1-2 min and lasted over-all for only 3.5-4.0 min. Glomerular filtration rate (G.F.R.) usually and filtration fraction (F.F.) always increased.3. Angiotensin II caused antidiuresis provided that the kidney had not been subjected either to salt loading or to haemodilution within the preceding 3 hr. These pretreatments converted the antidiuretic action of angiotensin into a diuresis.4. Angiotensin II raised the rate of Na excretion, the urinary concentration of Na and the urinary Na/K whether anti-diuretic or diuretic.

Glucose metabolism in renal tubular function

Heterogeneity of metabolic activity along the nephron points to a very varied relationship between glucose metabolism and ion transport. Glycolysis is linked closely to free-water clearance and possibly to sodium, potassium, and hydrogen ion transport. Glucose oxidation, while not the major source of renal energy, is crucial in sodium, potassium, and phosphate reabsorption. Gluconeogenesis recovers carbon compounds generated during the process of renal ammoniagenesis. Glucose synthesis and active sodium transport appear to compete for renal ATP, although no regulatory function for this competition has been identified. Glucose formed in the proximal tubule may support free-water clearance in adjacent distal tubule, but is not thought to contribute to any medullary function. The complex network of biosynthetic and catabolic pathways of glucose metabolism may have evolved in the kidney to protect the organism against wide variations in glucose demand which would otherwise be unavoidable during the course of rapidly fluctuating renal electrolyte loads.

Changes in proximal and distal tubular reabsorption produced by rapid expansion of extracellular fluid

Acute infusions of isotonic saline in the rat cause an increase in glomerular filtration rate and in the excretion of salt and water. The kidney swells, due to expansion of tubular and interstitial volume. Despite the increase in tubular diameter, transit time through the proximal tubules and loops of Henle is decreased, presumably owing to a greatly accelerated rate of tubular flow. Proximal tubular reabsorption, measured in blocked tubules, is inhibited in a way that cannot be ascribed to changes in tubular diameter. The prolongation of proximal reabsorptive half-time is not affected by the administration of aldosterone. It occurs equally in rats chronically loaded with or deprived of salt, and it is therefore not likely that it is influenced by the renal content of renin. In contrast, reabsorption from the distal convoluted tubule is enhanced by saline infusion. This change is observed in segments of tubules blocked with oil and isolated from their glomeruli and thus appears to occur independently of changes in glomerular filtration or tubular flow.

Natriuretic effect of angiotensin in dogs revealed after administration of reserpine and guanethidine

In untreated dogs anesthetized with morphine-chloralose, a small dose of angiotensin (0.0375 µg/kg per min) produced a large reduction in renal blood flow, a smaller reduction in glomerular filtration rate and an antinatriuresis. A graded change in the excretion of sodium in response to angiotensin occurred after the successive administration of reserpine and guanethidine. In reserpinetreated dogs, angiotensin did not produce an antinatriuresis, whereas in the same dogs after giving guanethidine, a natriuresis occurred in response to angiotensin (from a control of 60 to 189 µEq Na/min). The effects of angiotensin on blood pressure and glomerular filtration rate were similar in all dogs. The renal vasoconstrictor effect of angiotensin was decreased in 3 of 8 dogs after guanethidine. At the high dose of angiotensin (0.375 µg/kg per min), the natriuresis was larger (from a control of 75 to 353 µEq Na/min) and was unrelated to changes in glomerular filtration rate or renal blood flow. In reserpine- and guanethidine-treated dogs, angiotensin increased sodium excretion sufficiently during renal arterial constriction to produce a large reduction in renal blood flow and the filtered load of sodium. These results suggest that angiotensin has a renal tubular action that is uncovered by sympathetic blockade produced by reserpine and guanethidine.

Acute Infusion of Synthetic Angiotensin II in Patients with Essential Hypertension

Angiotensin II (1- l -asparaginyl-5- l -valyl angiotensin octapeptide) infused intravenously in subjects with idiopathic hypertension caused depression of the renal hemodynamics in all of them. In agreement with the findings of other investigators, more than one third of the patients showed a decrease in the rate of the sodium excretion; in the remaining subjects, the pressor infusion increased the excretion of sodium.

In all the hypertensive patients, angiotensin II favored renal reabsorption of water.

From the available evidence, it appears that angiotensin II acts upon the renal tubules. The reason for the opposite effect on sodium excretion in hypertensive patients remains unexplained.