Enhancement of corticosterone release by repeated injections of ACTH in the dexamethasone pre-treated rat.
To examine the possibility that pulsatile secretion of adrenocorticotrophic hormone (ACTH) enhances the responsiveness of the adrenal, the blood corticosterone response to repeated injections of ACTH was determined in the dexamethasone-nembutal pre-treated rat. Treatment with dexamethasone (100 micrograms/100 g body weight) at 13.00 h for 2 days decreased corticosterone levels and completely abolished these daily variations in both the blood and adrenal. Under these conditions, four or five successive iv injections of 0.2 or 2 mIU ACTH were given at 1/2 or 1 h intervals. Blood samples were taken immediately before and at frequent intervals after injection. A significant increase of blood corticosterone levels was observed 10 min after the second injection of 0.2 mIU ACTH. Further increases in blood corticosterone levels were observed after the subsequent injections. In addition, repeated injections of 2 mIU ACTH augmented the responsiveness of the adrenal to ACTH. The second or the third injections of 2 mIU ACTH produced a greater increase in adrenal corticosterone content than did the first ACTH injection. These results suggest that when ACTH acts on the adrenal gland in a pulsatile fashion, the steroidogenic response of the adrenal to ACTH increases markedly.
D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism; D000324:Adrenocorticotropic Hormone / Q000494:pharmacology*; D000818:Animals; D003345:Corticosterone / Q000097:blood / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D051381:Rats; D011919:Rats, Inbred Strains
D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D003345:Corticosterone