Angiotensin II natriuresis and antinatriuresis: role of renal artery pressure, renal hemodynamics, and tubular reabsorption.
The aim of this study was to determine the role of changes in renal artery pressure (RAP), renal hemodynamics, and tubular reabsorption in mediating the natriuretic and antinatriuretic actions of angiotensin II (AII). In anesthetized dogs, endogenous AII formation was blocked with SQ-14225 and AII was infused i.v. at rates of 5-1215 ng/kg/min while RAP was either servo-controlled at the normal level or permitted to increase. When RAP was servo-controlled to prevent a rise i RAP, AII infusion at all rates from 5-1215 ng/kg/min decreased urinary sodium excretion (UNaV) and fractional sodium excretion (FENa), while increasing fractional reabsorption of lithium (FRLi), an index of proximal tubule fractional sodium reabsorption and distal fractional sodium reabsorption (FRDNa): When RAP was permitted to increase, AII infusion rates up to 45 ng/kg/min decreased UNaV, and FENa, while increasing FRLi and FRDNa. However, at 135 ng/kg/min and above, UNaV and FENa increased while FRLi and FRDNa decreased when RAP was allowed to rise, even though RBF and FF were not substantially different from the values observed when RAP was servo-controlled. Filtered sodium load was slightly higher when RAP was permitted to increase during AII infusion, compared to the dogs in which RAP was servo-controlled, although the differences were not statistically significant. Thus, even very large doses of AII cause antinatriuresis when RAP was prevented from increasing. The natriuretic effect of high dose of AII is caused by increased RAP which decreases fractional sodium reabsorption in proximal and distal tubules and causes slight increases in sodium delivery to the tubules.
D000042:Absorption; D000804:Angiotensin II / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004285:Dogs; D005919:Glomerular Filtration Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects; D007684:Kidney Tubules / Q000378:metabolism*; D009318:Natriuresis / Q000187:drug effects; D012077:Renal Artery / Q000502:physiology*; D012964:Sodium / Q000378:metabolism
D000804:Angiotensin II; D012964:Sodium