Effects of Sex and Age on Growth Hormone Response to Growth Hormone-Releasing Hormone in Healthy Individuals

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Abstract
The influence of age and sex on human GH secretion is controversial. In previous studies, serum GH responses to arginine and insulin-induced hypoglycemia were significantly higher in pre- and postovulatory women than in men. In contrast, recent studies suggest that GH responsiveness to GHRH is higher in normal young men than in age-matched women. To clarify the question of sex and age influence on GHRH-(1–44)-stimulated GH secretion, we studied 116 normal women and men (with body mass indexes of 18–25 and 19–26, respectively) between the ages of 18 and 95 yr. The peak serum GH increments after GHRH administration were significantly higher in premenopausal women than in age-matched men (P < 0.003 for the age group 18–30 yr and P < 0.03 for the age group 30–50 yr, as assessed by analysis of variance). The responses were not different in postmenopausal women and age-matched men. Multiple regression analysis revealed a significant negative correlation between GHRH-induced GH responses (integrated area under the curve) and age in both women (P < 0.002) and men (P < 0.001). In addition, we determined basal serum testosterone, estradiol, cortisol, and PRL levels in all subjects. Multivariate regression analysis of the GH responses to GHRH administration revealed a significant positive correlation (P < 0.01) between serum estradiol and both GH increase and the area under the GH response curve. No correlation was found between GHRH-stimulated GH secretion and basal serum cortisol, testosterone, or PRL concentrations. Our data clearly demonstrate a marked influence of both sex and age on GHRH-stimulated GH secretion. We found a higher GH increase in premenopausal women compared with age matched-men and an age-dependent decrease in GHRH-stimulated GH secretion in both sexes. Furthermore, in women a significant influence of estradiol on GH secretion after GHRH administration could be demonstrated.