Somatomedin-C Stimulates Glycogen Synthesis in Fetal Rat Hepatocytes*

Abstract

The effects of somatomedin-C/insulin-like growth factor I (Sm-C) on glycogen metabolism in cultured hepatocytes from 20 day old rat fetuses were examined and compared with the effects of insulin. Sm-C (25-375 ng/ml; 3.25-50 nM) stimulated dose-dependent increases in [14C]glucose incorporation into glycogen (14.4-72.9%; P < 0.001) and total cell glycogen content (10.6-34.3%; P < 0.01). Maximal stimulation of glycogen synthesis by Sm-C occurred at 2-4 h of incubation. Insulin (10 nM-10 .mu.M) also stimulated [14C]glucose incorporation, but its potency was only 1/20th that of Sm-C. The time course of stimulation of glucose incorporation by insulin was identical to that of Sm-C, the dose-response curves of the 2 hormones were parallel, and the maximal effects of insulin were not enhanced by simultaneous exposure of cells to Sm-C. Apparently, Sm-C and insulin stimulate glycogenesis in fetal liver through similar or identical mechanisms. Since the potency of Sm-C was 20 times greater than that of insulin, the glycogenic action of insulin in fetal liver may be mediated through binding to a hepatic receptor which also binds Sm-C. In addition to having mitogenic effects on fetal tissues, Sm-C may have direct anabolic effects on fetal carbohydrate metabolism.