ATYPICAL PATTERN OF ADENYLYL-CYCLASE ACTIVITY IN THE ADRENAL-MEDULLA WITH AGE

Concurrent reduced physiological responsiveness often occurs in those tissues in which signal transduction coupled to adenylyl cyclase is di minished with age. In the adrenal medulla, the major physiological fun ctions are catecholamine synthesis and release, and these functions ar e increased with age. To examine whether the sensitivity or efficacy f or adenylyl cyclase stimulation is altered with age, we determined the vasoactive intestinal peptide (VIP) and forskolin activation of adeny lyl cyclase in adrenal medullary membranes from young (4 month) and se nescent (24 month) male F-344 rats. Stimulation by VIP (10 mu m) and G TP (10 mu m) were unchanged with age. in contrast, the maximal stimula tion by forskolin (100 mu m) and the sensitivity for forskolin stimula tion were increased with age. These data indicate that the pattern of increased adenylyl cyclase stimulation with age is comparable to that in liver tissue but atypical with respect to all other tissues in the rat.