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Local formation of angiotensin II (AII) within the kidney has been demonstrated. Changes in renal function induced by inhibitors of the renin-angiotensin system have been the basis for the postulate that AII may act as a paracrine substance in the kidney. We studied the renal action of chronic intrarenal infusions of AII at doses between 2 and 2000 fmol/kg X min in uninephrectomized conscious dogs monitored on 80 meq daily sodium intake. Exogenous AII was confined to the kidney, as demonstrated by the absence of systemic pressor and adrenal cortical responses during the intrarenal infusion. After 2 control days, each dose of AII was infused intrarenally for a period of 3 days. The smallest intrarenal dose of AII that caused significant antinatriuresis and antidiuresis was 20 fmol/kg X min. A significant reduction in urinary volume and sodium excretion occurred during the first 24 h of the infusion period and was proportionate to the amount of peptide infused. Renal escape from the antinatriuretic and antidiuretic effects of the peptide ensued on the second and third days of infusion. There were no significant changes in urinary potassium excretion, plasma renin activity (PRA), plasma aldosterone concentration, or blood pressure throughout the period of intrarenal AII administration. These data demonstrate dose-dependent direct antinatriuretic and antidiuretic actions of low AII concentrations. Escape from the sodium-retaining action of intrarenal AII occurred by 48 h and was independent of suppression of endogenous renin-angiotensin. These results indicate that AII alters renal function by direct intrarenal mechanisms.

The mechanism by which atrial natriuretic peptide (ANP) increases renal water and solute excretion is not fully understood. We studied the renal effects of ANP and angiotensin II (ANG II) separately and together in uninephrectomized conscious dogs (n = 7) in sodium metabolic balance (80 meq/day). Exogenous ANG II and ANP were without measurable systemic effects as demonstrated by absence of changes in blood pressure, plasma aldosterone concentration, and plasma renin activity. The quantity of ANG II that had significant renal effects that were without measurable systemic effects was 0.2 pmol.kg-1.min-1. Three infusion rates of ANP had significant renal effects (1, 10, and 20 pmol.kg-1.min-1). These quantities of ANP caused significant diuresis, natriuresis, kaliuresis, and increased glomerular filtration rate without significant changes in renal plasma flow. ANG II alone caused significant antidiuresis, antinatriuresis, and decreased glomerular filtration rate and renal plasma flow. When ANG II and ANP were given together, no change in urinary flow rate, urinary sodium or potassium excretion, or renal plasma flow was observed, whereas glomerular filtration rate increased. Filtration fraction increased significantly with ANG II and ANP separately and together. Intrarenal ANP prevents the ANG II-induced decrement in urinary sodium excretion and urine flow rate. ANP may play an important role in escape from the sodium-retaining action of intrarenal ANG II.

The maximum amounts of angiotensins II and III that were confined to the kidney during intrarenal arterial administration in conscious dogs were determined to be 2 and 12 pmol/kg X min, respectively. These doses were infused chronically intrarenally to uninephrectomized dogs. A significant reduction in urinary volume and excretion of sodium was observed at 24 h of the intrarenal peptide infusions. These excretory effects were more marked with angiotensin III than with angiotensin II. Escape from the antidiuretic and antinatriuretic effects of angiotensins II and III was observed after 24 h in spite of continuous administration of the peptides. To define the role of reduced intrarenal angiotensin concentration in the physiological phenomenon of escape from the sodium-retaining action of mineralocorticoids, angiotensin II or III at the above doses was administered intrarenally together with 11-deoxycorticosterone acetate. No delay in escape from the sodium-retaining effects of the mineralocorticoid was noted as a result of concurrent intrarenal angiotensin administration. In conclusion, both angiotensin II and angiotensin III have direct sodium- and volume-retaining effects on the kidney. These renal effects are abolished within 48 h, either due to tachyphylaxis to angiotensins or by other mechanisms overriding the actions of angiotensins. No association was demonstrated between suppression of the renin-angiotensin system and escape from mineralocorticoid-induced sodium retention.