PHYSIOLOGICAL ACTIONS OF ANGIOTENSIN-II MEDIATED BY AT(1) AND AT(2) RECEPTORS IN THE BRAIN

1. Autoradiographic binding studies have shown that the AT(1) receptor is the predominant angiotensin II (AngII) receptor subtype in the cen tral nervous system (CNS), Major sites of AT(1) receptors are the lami na terminalis, hypothalamic paraventricular nucleus, the lateral parab rachial nucleus, rostral and caudal ventrolateral medulla, nucleus of the solitary tract and the intermediolateral cell column of the thorac o-lumbar spinal cord, 2, While there are differences between species, AT(2) receptors are found mainly in the cerebellum, inferior olive and locus coeruleus of the rat, 3. Circulating AngII acts on AT(1) recept ors in the subfornical organ and organum vasculosum of the lamina term inalis (OVLT) to stimulate neurons that may have a role in initiating water drinking, 4, Centrally administered AngII may act on AT(1) recep tors in the median preoptic nucleus and elsewhere to induce drinking, sodium appetite, a sympathetic vasoconstrictor response and vasopressi n secretion, 5, Recent evidence shows that centrally administered AT(1 ) antagonists inhibit dipsogenic, natriuretic, presser and vasopressin secretory responses to intracerebroventricular infusion of hypertonic saline, This suggests that an angiotensinergic neural pathway has a r ole in osmoregulatory responses, 6. Central angiotensinergic pathways which include neural inputs to the rostral ventrolateral medulla may u se AT(1) receptors and play a role in the function of sympathetic path ways maintaining arterial pressure.