EXPRESSION OF A NOVEL ANGIOTENSIN-II RECEPTOR SUBTYPE IN GERBIL BRAIN

Angiotensin II receptors are highly localized in adult gerbil brain. A pparent receptor number is high in subfornical organ, vascular organ o f the lamina terminalis, nucleus of the solitary tract, hippocampus, a nd in the anterior pituitary gland. In the hippocampus, binding is loc alized to the stratum oriens, radiatum, the lacunar molecular layers o f the CA1 subfield, and the molecular layer of the gyrus dentatus, wit h a medial to lateral and anterior to posterior gradient in receptor e xpression. Binding is absent from the pyramidal layer of the CA1 subfi eld and from the granular cell layer of the gyrus dentatus, areas rich in angiotensin IV binding. Characterization in the hippocampus reveal ed the presence of a high affinity receptor, sensitive to incubation w ith the guanine nucleotide GTP gamma S, and displaced by angiotensin I I = angiotensin III < Sar(1)-Ile(8)-angiotensin II, but not by angiote nsin IV or other angiotensin fragments, the AT(1) receptor antagonist losartan, or the AT(2) ligands CGP 42112 or PD 123177. In other brain areas, binding was equally insensitive to displacement by AT(1) or AT( 2) ligands, with the exception of binding in the olfactory bulb, which was totally displaced by CGP 42112 and PD 123177, but not by losartan . In the gerbil, most of the brain and pituitary angiotensin II recept ors are different from the AT(1), AT(2) and AT(4) subtypes, and should be considered 'atypical' until further characterization.