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 DEX on OH release throughout the menstrual cycle. DESIGN A within subjects, randomized double-blind counter-balanced design was employed. METHODOLOGY Baseline levels Of GH, oestradiol and progesterone were taken at three the points In two consecutive menstrual cycles, after which 4mg of oral DEX or placebo was administered. Plasma samples for OH estimation were taken at 60,180,240 and 300 minutes. Each woman was tested 6 times, 3 times with placebo and 3 times with DEX. SUBJECTS Six women with regular menstrual cycles were studied. MEASUREMENTS Plasma OH, oestradiol and Progesterone were measured by radioimmunoassay. RESULTS When expressed as maximum change from base line (AGH) mean OH responses to DEX Increased Incrementally from early (12·2 ± 2·5 μ/I), through mid (25·6 ± 33 μ/I) to late (37·2 ± 3·5 μ/I) 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 the points are different from those during the follicular phase (P < 0.05) and differences between mid-cycle and luteal phases just fall to reach significance (P < 015). Responses to placebo did not vary from baseline. Plasma oestradiol values were significantly correlated with GH responsivity to active drug throughout the cycle (P < 0.05); the same was not true of progesterone. CONCLUSION Our study has demonstrated that dexa-methasone-mediated GH release shows a stepwise Increase throughout the menstrual cycle.