| Abstract: | ACTH, a prolonged action hormone, in a dose of 2.5 mu. was injected into guinea pigs daily for 5-35 days. The adenylate cyclase activity of the crude adrenal membrane fraction and the activity of cAMP-dependent protein kinases in the cytoplasmic fraction were determined. Cyclic changes in the basal and stimulated adenylate cyclase activities occurring with 15-20-day intervals have been established for the first time. The sensitivity of adenylate cyclase to ACTH, NaF and GTP did not change in the course of two cycles. The activity of cAMP-dependent protein kinases increased during the first few days after ACTH administration and decreased after further injections of the hormone. The role of cyclic changes of the enzyme activity in the mechanism of proliferative effect of ACTH is discussed. |
