Type I receptors in parotid, colon, and pituitary are aldosterone selective in vivo
Sheppard, K.; Funder, J.W.
American Journal of Physiology 253(4 Pt 1): E467-E471
1987
ISSN/ISBN: 0002-9513 PMID: 2821824 Document Number: 304056
Previous in vivo studies have demonstrated that type I receptors in the rat kidney are aldosterone selective, whereas those in the hippocampus do not appear to discriminate between aldosterone and corticosterone. We have injected mature rats with [3H]aldosterone or [3H]corticosterone plus 100-fold excess of RU 28362, with or without unlabeled aldosterone or corticosterone, and compared type I receptor occupancy in two classic mineralocorticoid target tissues (parotid and colon) and in the pituitary: Mature rats were killed 10-180 min after tracer administration; [3H).alpha.ldosterone was well taken up and retained in all tissues, whereas [3H]corticosterone was significantly retained only in the pituitary 10 min after tracer administration. To assess a possible role for corticosterone-binding globulin (CBG) in conferring aldosterone specificity on type I receptors, 10-day-old rats (with very low levels of CBG) were similarly injected. In the colon and parotid, [3H]aldosterone binding was at least an order of magnitude higher than that of corticosterone; in the pituitary aldosterone binding was approximately three times that of corticosterone. We interpret these data as evidence that in the parotid and colon type I receptors are aldosterone selective by a non-CBG-requiring mechanism, whereas in the pituitary there appear to be both aldosterone-selective and nonselective type I sites.