Estrogen Stimulates Growth Hormone and Somatomedin-C in Castrate and Intact Female Baboons

Abstract

To evaluate the effects of physiological concentrations of estrogen on plasma concentrations of somatomedinC (Sm-C) and GH, 16 chronic castrate female baboons were implanted either with blank Silastic capsules (n = 5) or capsules containing crystalline estradiol (E₂; n = 11), which remained in place for 7 days. By day 7, serum E₂ levels in treated animals rose into the physiological adult female range (mean ± SEM, 96 ± 9.2 pg/ml) and were greater (P < 0.0005) than those in control animals (27.5 ± 3.4 pg/ml). Sm-C concentrations rose significantly by day 7 in treated animals compared to those in control animals, whether assayed from unprocessed plasma (96% in crease; P < 0.01), plasma pretreated with glycine-HCl (99% increase; P < 0.01), or plasma extracted with acid-ethanol (72% increase; P < 0.02). GH concentrations in these animals were low and were not significantly different in E₂-treated and control)animals. To evaluate the effects of pharmacological doses of E₂ on Sm-C and GH concentrations, six intact adult female baboons were treated with six daily injections (of 1 mg E₂ benzoate in oil. Serum E₂ rose to a mean level of 1669 ± 320 pg/xml on day 7. The plasma Sm-C concentration by day 7 was significantly higherthan the pretreatment value whether assayed in untreated plasma (4.3-fold increase; P < 0.01), plasma pretreated with glycine-HCl (2-fold increase; P < 0.01), or plasma extracted with acid-ethanol (1.7-fold increase; P < 0.01). Mean serum GH concentrations rose significantly from 3.3 ng/ml on day 0 to 23.6 ng/ml by day 7 (P < 0.02). Evaluation of the chromatographic profile of native baboon plasma suggested a marked increase in [¹²⁵I]Sm-C binding to plasma proteinsafter in vivo pharmaco(logical E₂ treatment; a broad peak of [¹²⁵I]Sm-C binding over a size range from that of albumin to γ-globulin was found. These results indicate that estrogen treatment of castrate or intact female baboons with both physiological and pharmacological doses results in an increase in plasma Sm-C concentrations that, at least in pharmacological doses, are mediated through an increase in GH concentrations. Although(pharmacological E₂ treatment results in a stimulation of plasma proteins that bind Sm-C, the effects on plasma Sm-C concentrations were found after procedures that diminish interference from circulating binding proteins. These data support the concept that estrogen may play a role in the physiological increase in plasma concentrations of Sm-C associated with normal puberty. (J Clin En-docrinol Metab58: 698,1984)