Increased Number of Angiotensin II Binding Sites Determined by Autoradiography in Anterior Pituitary of Water-Deprived and Brattleboro Rats

Abstract

Pituitary angiotensin II (ANG) binding sites were characterized by autoradiography in individual male Long Evans (LE) rats, heterozygous Brattleboro (HZ) rats, and homozygous Brattleboro (DI) rats which were water satiated or water deprived. An additional group of DI rats was treated with arginine vasopressin for I week. The technique utilized 8-!rm pituitary sections which were incubated with rxI-[Sar¡]-ANG in concentrations ranging from 25 pM to l0 nM. Angiotensin binding in the anterior pituitary of water-satiated LE rats was characterized by a single class of high-affinity, saturable sites with a B."" of 1.309n Il9 fmol/mg of protein and a K" of 0.51+0.03 x l0' M r. Compared to LE rats the density of ANG-binding sites in antedor pituitary was higher in DI rats ( + 84.2%), with HZ haying an intermediate concentration ( + 41.6). Dehydration increased the ANc-binding site density in all groups. Five days of water deprivation increased the number of ANG-binding sites by 86.5% and by 3ó.9% in LE and HZ rats, respectively, when compared to their water-satiated controls. After I day ofwater deprivation, the ANc-binding site density increased by 19.4% in Dl rats. No changes in ANG-binding sites occurred after hormonal replacement with arginine vasopressin in water-satiated DI rats. The binding afFrnity constant of the agonist for the ANG-binding sites compared with LE rats was decreased in both HZ and DI rats (-27 .5 znd -19.4o/o) and was also decreased after 5 days of dehydration in LE rats (-34%) when compared to the water-satiated state. Our results demonstrate alterations in ANG-binding sites in the anterior pituitary gland of both dehydrated B¡attleboro rats and LE rats. These findings suggest a role for anterior pituitary ANG receptors in the regulation of fluid metabolism in the rat.