Depending on the time of administration, dexamethasone potentiates or blocks growth hormone-releasing hormone-induced growth hormone release in man.
In humans, corticoids suppress growth hormone (GH) secretion elicited by a variety of stimuli, while in vitro they potentiate GH release. To further study this problem, the effect of two doses of dexamethasone on GH secretion elicited by GH-releasing hormone (GHRH) in 6 normal volunteers was studied. Each subject underwent three tests, on 3 separate days with GHRH 1-29 (1 microgram/kg i.v. at 12.00 h). On the control day, only GHRH was given, on the second day dexamethasone 4 mg i.v. was administered at 09.00 h (3 h before GHRH) and on the third day dexamethasone 8 mg p.o. was given 12 h before GHRH (at 00.00 h). The GHRH-induced GH peak was 9.9 +/- 2.0 ng/ml, while 4 mg dexamethasone significantly (p less than 0.05) potentiated GH secretion elicited by GHRH (29.2 +/- 5.7 ng/ml). When dexamethasone 8 mg was given 12 h before, GHRH-induced GH secretion was completely blocked (3.0 +/- 1.1 ng/ml) (p less than 0.05). These results indicate that corticoids have two different actions: an acute potentiating activity on GHRH, and a delayed blocking action on GHRH-induced GH secretion.
D000328:Adult; D003907:Dexamethasone / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004347:Drug Interactions; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage* / Q000494:pharmacology; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007275:Injections, Intravenous; D008297:Male
D003907:Dexamethasone; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D006854:Hydrocortisone