Demonstration of In Vitro Actions of Growth Hormone on Isolated Rat Adipocytes

Abstract

Previous studies have shown that adipocytes isolated from normal rats possess specific receptors for growth hormone (GH). Thus, we have now investigated the direct effects on such cells of GH added in vitro. The biological actions of GH determined were the stimulation of ¹⁴C-glucose oxidation to ¹⁴CO₂ and conversion to ¹⁴C-lipid. As in adipose segments, hGH stimulation of these parameters required a 3-4 hr preincubation period in GH-free medium. The effect of hGH or hGH was dose-dependent with maximal effects at 1-2 μg/ml (CO₂ 55±13% stimulation above basal n=9; lipid 33±4% n=21, mean ± SEM). The magnitude of the effect in isolated adipocytes was lower than that seen in adipose segments from similar groups of animals (lipid 67 ± 26%, n=4). The induction of responsiveness by preincubation was accompanied by a parallel increase in ¹²⁵I-hGH binding. These studies have demonstrated that adipocytes from normal rats not only possess specific receptors for GH but also are metabolically responsive to GH added in vitro. These data suggest that the isolated rat adipocyte should be a useful model for further investigation of the relationship between GH receptor and post-receptor events.