ANGIOTENSIN AND RENAL NA-K ACTIVATED ADENOSINE TRIPHOSPHATASE. (STUDIES ON NA-K ACTIVATED ATPASE, VIII)

Effect of angiotensin II and captopril on renal tubular function in man

The effects of nonpressor doses of intravenous angiotensin II and of the converting enzyme inhibitor captopril on renal excretory function were investigated in eight healthy volunteers during sustained water diuresis on a constant intake of 150 mmol sodium per day. The angiotensin II-analogue val5-angiotensin II-asp1-beta-amide was infused i.v. at an average dose of 2.6 ng kg-1 min-1 which was the highest dose without a significant effect on arterial blood pressure. This subpressor dose of angiotensin II significantly decreased urine volume, urinary excretion of sodium, chloride and phosphate and distal delivery [(CH2O + CCl)/GFR X 100] in the absence of changes in GFR or distal fractional chloride absorption [CH2O/(CH2O + CCl)]. In a second series of experiments, an oral dose of 50 mg of the angiotensin I-converting enzyme inhibitor captopril was given to the sodium replete volunteers. In this study, captopril did not affect arterial blood pressure, GFR or any of the determined parameters of renal tubular function. Our results strongly suggest that the nonpressor dose of angiotensin II induced renal retention of sodium chloride via increased absorption in the proximal tubule. Thus, they further support the concept that angiotensin II participates in the regulation of renal sodium chloride excretion by affecting proximal tubular absorptive capacity. However, in the sodium replete stage, angiotensin II is of no major importance in regulating sodium chloride excretion.

The effect of angiotensin on cation transport by rat kidney cortex slices

1. A study has been made of the effect of angiotensin (10(-12) g/ml.) on active and passive transport of sodium, potassium and water between rat kidney cortex slices and the incubation medium.2. Angiotensin has no effect on the passive uptake of sodium and loss of potassium by slices incubated under conditions which inhibit active transport.3. Active sodium extrusion by slices incubated under aerobic conditions is stimulated, whereas active potassium uptake is inhibited by angiotensin.4. Sodium pump activity is stimulated by angiotensin in the presence of ouabain or in the absence of potassium in the incubation medium, conditions which block the sodium for potassium exchange pump.5. There is a 2 min latent period following the application of angiotensin before a response is observed.6. These findings are discussed in relation to the mechanism of action of angiotensin on kidney sodium and fluid transport processes.

Renal tubular flow dynamics during angiotensin diuresis in the rat

1. Tubular size and lissamine green transit times were measured in rat kidneys undergoing a diuretic response to angiotensin II (0.5 mug/kg per min), and compared with the changes observed during diuresis induced by osmotic diuretics, noradrenaline and chlorothiazide.2. Angiotensin always caused a marked prolongation in proximal and distal tubular transit times; individual distal convolutions were coloured for prolonged periods, and lissamine green appeared in high concentration in distal tubules.3. Marked changes were observed in superficial tubular calibre during a stable diuretic response to angiotensin. Where distal tubular diameter was normal for the rate of urine flow, proximal tubular volume was generally reduced. In a number of experiments, however, distal tubules were markedly dilated, and in these cases proximal tubular volume was also often increased. Angiotensin may therefore be capable of causing a degree of internal hydronephrosis in the rat kidney.4. Prolongation of dye transit times, and the appearance of a concentrated lissamine green bolus in distal tubules, was suggestive of a decreased superficial nephron flow rate, indicating that the diuretic effect of angiotensin may take place only through deeper nephrons.