Dehydroepiandrosterone restoration of growth hormone gene expression in aging female rats, in vivo and in vitro: evidence for actions via estrogen receptors.

A decline in dehydroepiandrosterone (DHEA) and GH levels with aging may be associated with frailty and morbidity. Little is known about the direct effects of DHEA on somatotropes. We recently reported that 17beta-estradiol (E2), a DHEA metabolite, stimulates the expression of GH in vitro in young female rats. To test the hypothesis that DHEA restores function in aging somatotropes, dispersed anterior pituitary (AP) cells from middle-aged (12-14 months) or young (3-4 months) female rats were cultured in vitro with or without DHEA or E2 and fixed for immunolabeling or in situ hybridization. E2 increased the percentage of AP cells with GH protein or mRNA in the aged rats to young levels. DHEA increased the percentages of somatotropes (detected by GH protein or mRNA) from 14-16 +/- 2% to 29-31 +/- 3% (P < or = 0.05) and of GH mRNA (detected by quantitative RT-PCR) only in aging rats. To test DHEA's in vivo effects, 18-month-old female rats were injected with DHEA or vehicle for 2.5 d, followed by a bolus of GHRH 1 h before death. DHEA treatment increased serum GH 1.8-fold (7 +/- 0.5 to 12 +/- 1.3 ng/ml; P = 0.02, by RIA) along with a similar increase (P = 0.02) in GH immunolabel. GHRH target cells also increased from 11 +/- 1% to 19 +/- 2% (P = 0.03). Neither GH nor GHRH receptor mRNAs levels were changed. To test the mechanisms behind DHEA's actions, AP cells from aging rats were treated with DHEA with or without inhibitors of DHEA metabolism. Trilostane, aminogluthemide, or ICI 182,780 completely blocked the stimulatory effects of DHEA, suggesting that DHEA metabolites may stimulate aging somatotropes via estrogen receptors.