Résumé
Ageing effects on the in vivo cyclic 3, 5'- adenosine monophosphate [cAMP] production by the adrenal cortex were studied in the rat. Eleven old [from 23 to 29 months] and 13 young [from 4 to 5 months], dexamethasone pre-treated Long-Evans female rats received 5.0 mu.i. [1-24] ACTH/100g b.w. by intravenous injection. The plasma concentration of corticosterone as well as the adrenal contents in cAMP and corticosterone were measured, by radioimmunoassay, just before and 45 min after the [1-24] ACTH injection. The basal plasma corticosterone level and the adrenal contents in corticosterone and cAMP were low and no group difference was observed. The [1-24] ACTH injection causes significant increases in the plasma corticosterone level and the glandular contents in corticosterone and cAMP, which were lesser in the old animals than in the young ones; the differences aged/young were approximately -37%, -18% and -55% respectively. These results suggest that the reduced sterodogene response of the adrenal cortex in the old rat, to an acute ACTH administration is at least partly due to a decrease in the cellular production of the principal second messenger of this hormone, i.e. the cAMP