title: Release of corticosterone from the rat adrenal cortex in response to administration of (1-24)adrenocorticotrophin.
abstract: The intraperitoneal injection of (1-24)ACTH (34-170 nmol/kg) in rats pretreated with betamethasone resulted in a biphasic rise in plasma corticosterone; only a single phase-response was observed after lower doses (3.4-17.0 nmol/kg). There was an initial rapid rise to a level of approximately 0.72 mumol corticosterone/l plasma over the first 10 min after injection, followed by a plateau phase in which there was no further significant rise in steroid levels up to 25 min. Between 25 and 30 min after injection there was a second significant rise in plasma corticosterone concentration. The amplitude of the first phase of steroid increase was essentially the same for all doses of (1-24)ACTH administered whereas the amplitude of the second phase was dose-dependent. The administration of the microtubule inhibitor, colchicine, greatly reduced the amplitude of the second phase of the response to (1-24)ACTH while not affecting the first phase. However, a second stimulus with (1-24)ACTH in colchicine-treated animals was without effect on plasma corticosterone concentrations; both the first and second phases of corticosteroid increase being abolished. It is proposed that the first phase of plasma corticosterone increase resulted from the release of corticosteroid from a storage form close to the cell membrane and not requiring microtubular transport, whereas the second phase was the result of transport from more distant storage sites or de-novo synthesis.
mesh_terms: D000302:Adrenal Cortex / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D000324:Adrenocorticotropic Hormone / Q000031:analogs & derivatives*; D000818:Animals; D001623:Betamethasone / Q000494:pharmacology; D003078:Colchicine / Q000494:pharmacology; D003345:Corticosterone / Q000097:blood / Q000378:metabolism*; D003366:Cosyntropin / Q000494:pharmacology*; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D003366:Cosyntropin; D000324:Adrenocorticotropic Hormone; D001623:Betamethasone; D003078:Colchicine; D003345:Corticosterone