DIURNAL-VARIATION OF GROWTH-HORMONE RESPONSES TO ACUTELY ADMINISTEREDDEXAMETHASONE IN HEALTHY MALE-VOLUNTEERS

Acute administration of exogenous corticosteroids stimulates growth ho rmone (GH) release. Physiological fluctuations of plasma cortisol appe ar to have an effect on the circadian release of GH. The purpose of th is study was to examine the effects of the diurnal variation of plasma cortisol on dexamethasone (DEX)-induced GH responses in healthy volun teers. Six healthy male subjects were studied using a randomised cross -over design. Subjects were tested twice, with an interval of two week s between tests, at 9.00 h and 14.00 h. After baseline levels for GH a nd cortisol were taken, subjects received 4 mg of oral DEX and blood s amples were drawn at +60, +180, +240 and +300 minutes later. GH levels peaked 3 hours post-DEX administration and were greater in the mornin g than in the afternoon. Mean +/- SEM Delta GH values at 9.00 h and 14 .00 h were 14.1+/-2.7 ng/ml and 6.9+/-1.6 ng/ml, respectively (t=2,36, df= .10, p<0.04). DEX-induced GH release appears to undergo a diurnal variation.