Binding of Angiotensin by Neurohypophysis and Adenohypophysis in Vivo and in Vitro

Abstract

Following intra-arterial injection of 125I-labeled angiotensin I in vivo (which is presumed to be converted to angiotensin II), there was similar and significant accumulation of label by both lobes of the [rat] pituitary. Other regions of the brain including the hypothalamus showed very little uptake of label. In vitro incubations of both pituitary lobes with angiotensin I showed that the neurohypophysis bound more hormone per unit weight than the adenohypophysis, and that a portion of the binding in both lobes was saturable. Studies with angiotensin II in vitro showed that both lobes could concentrate label equally to a level 5 times that of the medium. A plateau in binding occurred at 30 min for both lobes, which is consistent with the interpretation that a portion of this binding is also saturable. Most actions of angiotensin II occur within 5 min, so the peak in binding at 30 min may not be related to a physiological action of angiotensin II on the neurohypophysis or adenohypophysis. The physiological correlates of angiotensin I and II binding by both pituitary lobes in vivo and in vitro remain to be established.