Effects of chronic treatment with adrenocorticotropin on adenylate cyclase activity in the adrenal cortex.

The effects of prolonged administration of ACTH in vivo on adenylate cyclase activity in the zona glomerulosa (the capsular fraction) and the zona fasciculata-reticularis (the decapsulated fraction) of rat adrenocortical glands were investigated. Hyperresponsiveness of adenylate cyclase activity to ACTH in vitro was observed for both the capsular and the decapsulated fractions from ACTH-treated rats with a similar magnitude of stimulation by NaF, the guanine nucleotide or forskolin. There were no differences in binding sites for ACTH in membranes between the ACTH- and the saline-treated rats. The augmenting effects of the in vivo ACTH treatment on the enzyme stimulated by ACTH were accompanied by an increased sensitivity to the guanine nucleotide, suggesting that ACTH treatment in vivo was followed by an increased efficacy in coupling of the ACTH receptors to the adenylate cyclase complex associated with the guanine nucleotide regulatory components.