Role of angiotensin in the osmotic control of vasopressin release by the organ-cultured rat hypothalamo-neurohypophyseal system.

Abstract

Angiotensin II (AII) appears to either mediate or modulate osmotically stimulated vasopressin (VP) release by the organ-cultured rat hypothalamo-neurohypophyseal system. Saralasin, an AII antagonist, blocked VP release in response to a 10-mosmol increment in culture medium osmolality achieved by the addition of NaCl. This was observed at all concentrations tested (10(-7), 10(-6), 10(-4) M). Saralasin (10(-4) M) also blocked VP release in response to a comparable mannitol-induced increase in osmolality. Since nicotinic-cholinergic antagonists previously were shown to inhibit osmotically stimulated VP release, the effect of hexamthonium, a nicotinic, a nicotinic-cholinergic antagonist, on AII-stimulated VP release was examined. Hexamethonium (10(-5)-10(-3) M) was ineffective in blocking AII stimulation of VP release. This finding coupled with the previous observation that saralasin does not block acetylcholine stimulation of VP release suggests independent AII and cholinergic mechanisms controlling VP release; however, the effectiveness of both types of antagonists in blocking osmotically stimulated VP release indicates some interaction between these regulators of VP release.