Control of renal and extrarenal salt and water excretion by plasma angiotensin II in the kelp gull (Larus dominicanus)

Abstract

The osmoregulatory effects of intravenously (i.v.) administered angiotensin II (AII) at dose rates of 5, 15 and 45 ng.kg-1.min-1 were examined in kelp gulls utilizing salt gland and/or kidneys as excretory organs. In birds given i.v. infusion of 1200 mOsmolal NaCl at 0.3 ml.min-1 and utilizing only the salt glands to excrete the load, infusion of AII for 30 min consistently inhibited salt gland function in a dose-dependent manner. In birds given i.v. infusion of 500 mOsmolal NaCl at 0.72 ml.min-1 and utilizing both salt glands and kidneys to excrete the load, each dose of AII given for 2 h inhibited salt gland function but stimulated the kidney, so that the overall outputs of salt and water were enhanced and showed significant (2P less than 0.01) positive correlations with plasma AII. In birds given i.v. infusion of 200 mOsmolal glucose at 0.5 ml.min-1 and utilizing only the kidneys to excrete the load, low doses of AII (5 and 15 ng.kg-1.min-1) caused renal salt and water retention, whereas a high dose (45 ng.kg-1.min-1) stimulated salt and water output. The actions of plasma AII in kelp gulls support the concept that this hormone plays a vital role in avian osmoregulation, having effects on both salt gland and kidney function. Elevation of plasma AII consistently inhibits actively secreting salt glands, but its effects upon renal excretion depend primarily on the osmotic status as well as on the plasma AII concentration. In conditions of salt and volume loading doses of AII stimulate sodium and water excretion. With salt and volume depletion, the action of AII is bi-phasic with low doses promoting renal sodium and water retention but high circulating levels causing natriuresis and diuresis.