DIFFERENTIAL-EFFECTS OF ESTROGEN AND MEDROXYPROGESTERONE ON BASAL ANDSTRESS-INDUCED GROWTH-HORMONE RELEASE, IGF-1 LEVELS, AND CELLULAR-IMMUNITY IN POSTMENOPAUSAL WOMEN

We evaluated the influence of continual estrogen replacement therapy ( ERT) as presently practiced by postmenopausal women with conjugated es trogens and medroxyprogesterone acetate (MPA) on the growth hormone/in sulin-like growth factor-1 (GH/IGF-1) axis and cellular immunity. Thir ty-nine postmenopausal women were evaluated (12 on no replacement, 14 on estrogen only, and 13 on estrogen and MPA). In the women receiving only conjugated estrogens, increased GH levels and decreased IGF-1 lev els were found, which replicated previous research and probably reflec ted estrogen inhibition of hepatic IGF-1 production with a secondary i ncrease in GH release because of reduced feedback inhibition. In women taking both MPA and estrogen, GH was increased and the previously obs erved estrogen induced decrease in IGF-1 levels was inhibited. In orde r to determine the influence of ERT on psychosocial stress-induced GH release, math (mental stress) and speech (social stress) challenges we re utilized, and they produced significant increases in heart rate in all three groups. The heart rate following stress was significantly en hanced by estrogen replacement. These stressors also led to increased GH secretion in the women taking estrogen and MPA, but not in the othe r two groups. Gonadal steroids and GH can influence cellular immunity. We observed that ERT in both groups was associated with significantly enhanced lymphocyte responsiveness to the T-cell mitogens phytohemagl utinin (PHA) and Conconavalin A (Con A), and basal GH levels were corr elated with the PHA response in the estrogen only group. ERT did not i nfluence natural killer (NK) cell activity. We also found significant differences in the steady-state expression of lat ent Epstein-Barr vir us (EBV) with increased antibody titers in the women in the estrogen o nly group and lower antibody titers in the MPA plus estrogen group. GH levels were correlated with EBV antibody titers in the estrogen plus MPA group. This study supports the hypothesis that GH and immune modul ation can be influenced by ERT in postmenopausal woman. Given the exta nt literature on the immune-enhancing effects of CH, these data sugges t that ERT may slow the decline of GH secretion with aging, an event t hat has been implicated in immunosenescence.