Angiotensin II receptor subtypes in the duck subfornical organ: an electrophysiological and receptor autoradiographic investigation

Abstract

The pharmacology of angiotensin II (AngII) receptors was investigated in the brain of ducks using receptor autoradiographic and electrophysiological methods. Using 125I[Val 5]AngII as a ligand, specific binding was observed in sections of the duck adrenal gland and in several brain areas involved in body fluid homeostasis. Displacement studies using the same antagonists as used for classifying mammalian AngII receptor subtypes revealed that the rank order of potencies in competition with AngII receptors in the adrenal gland and in the subfornical organ was: AngII > CGP-42112A > losartan > PD-123319. Electrophysiological recordings from spontaneously active neurons of duck SFO slices revealed that the majority of neurons could be excited by AngII (10 −7 M). The excitatory effect of AngII could be partially inhibited by CGP-42112A (10 −5 M), which proved to be more effective than equimolar losartan and far more effective than PD-123319. These data suggest that the neuronal AngII receptors in the SFO are pharmacologically distinct from the mammalian AT 1- and AT 2-receptors. Further, central AngII receptors of ducks share common pharmacological characteristics with AngII receptors in the duck adrenal gland and peripheral organs of other bird species.