Estrogen stimulates growth hormone and somatomedin-C in castrate and intact female baboons.

To evaluate the effects of physiological concentrations of estrogen on plasma concentrations of somatomedin-C (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 less than 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% increase; P less than 0.01), plasma pretreated with glycine-HCl (99% increase; P less than 0.01), or plasma extracted with acid-ethanol (72% increase; P less than 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/ml on day 7. The plasma Sm-C concentration by day 7 was significantly higher than the pretreatment value whether assayed in untreated plasma (4.3-fold increase; P less than 0.01), plasma pretreated with glycine-HCl (2-fold increase; P less than 0.01), or plasma extracted with acid-ethanol (1.7-fold increase; P less than 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 less than 0.02). Evaluation of the chromatographic profile of native baboon plasma suggested a marked increase in [125I]Sm-C binding to plasma proteins after in vivo pharmacological E2 treatment; a broad peak of [125I]Sm-C binding over a size range from that of albumin to gamma-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.