Effects of aging and estradiol supplementation on GH axis dynamics in women

GH and IGF-I secretion decrease with age. The decline in serum GH with age appears to be associated with menopause. Prior studies of GH release before and after oral and transdermal hormonal replacement in the postmenopausal patient have shown no change or an increase in GH secretion. To distinguish the somatotropic axis effects of aging from those of estrogen deficiency, we compared eight prematurely menopausal women, aged 25-40 yr, with eight postmenopausal women, aged 51-70 yr, both before and after estradiol replacement. All women had a body mass index below 28 kg/m2. All were evaluated twice with frequent blood sampling every 10 min for 24 h. Studies were performed in the absence of exogenous hormones and 6-8 wk after transdermal estradiol replacement, targeted to achieve a serum estradiol level of 367 pmol/liter. GH pulsatility was analyzed. Variables tested included mean GH levels, interpulse baseline mean, pulse frequency per 24 h, and pulse amplitude. Transdermal estrogen replacement had a significant effect on mean GH levels and mean basal GH levels in both the premature ovarian failure and the age-appropriate postmenopausal group. No differences were noted in GH pulse frequency, GH pulse amplitude, IGF-I, IGF-binding protein-1, and IGF-binding protein-3 before and after treatment. A pronounced age effect was noted between the two groups. The premature ovarian failure women secreted significantly greater mean GH than the age-appropriate postmenopausal group regardless of treatment, with a significance level of P = 0.026. Interpulse baseline GH means were greater in the premature ovarian failure women than in the age-appropriate postmenopausal group, but the significance of this relationship was obliterated after adjustment for body mass index. Pulse amplitude was significantly increased in the premature ovarian failure women compared with age-appropriate postmenopausal women (P = 0.006). No significant changes were detected in the GH pulse frequency between the premature ovarian failure and postmenopausal groups. We conclude that moderate doses of transdermal estradiol supplementation do not exert a great effect on the somatotropic axis in women. Age and body composition appear to be the predominant influences on GH activity in women.