GROWTH-HORMONE RESPONSES TO DEXAMETHASONE IN HEALTHY FEMALES THROUGHOUT THE MENSTRUAL-CYCLE

OBJECTIVE In health, acute administration of dexamethasone (DEX) leads to growth hormone release. As sex steroids have a profound influence on the somatotrophic axis, we decided to investigate the effects of DE X on GH release throughout the menstrual cycle. DESIGN A within subjec ts, randomized double-blind counter-balanced design was employed. METH ODOLOGY Baseline levels of GH, oestradiol and progesterone were taken at three time points in two consecutive menstrual cycles, after which 4 mg of oral DEX or placebo was administered. Plasma samples for GH es timation were taken at 60, 180, 240 and 300 minutes. Each woman was te sted 6 times, 3 times with placebo and 3 times with DEX. SUBJECTS Six women with regular menstrual cycles were studied. MEASUREMENTS Plasma GH, oestradiol and progesterone were measured by radioimmunoassay. RES ULTS When expressed as maximum change from base line (Delta GH) mean G H responses to DEX increased incrementally from early (12.2 +/- 2.5 mU /l), through mid (25.6 +/- 3 3 mU/l) to late (37.2 +/- 3.5 mU/l) cycle . This represents a significant effect of cycle phase on GH responses to DEX (P < 0.05). GH responses at both the mid-cycle and the luteal t ime points are different from those during the follicular phase (P < 0 .05) and differences between midcycle and luteal phases just fail to r each significance (P < 0.15). Responses to placebo did not vary from b aseline. Plasma oestradiol values were significantly correlated with G H responsivity to active drug throughout the cycle (P < 0.05); the sam e was not true of progesterone. CONCLUSION Our study has demonstrated that dexamethasone-mediated GH release shows a stepwise increase throu ghout the menstrual cycle.