Effect of zinc on the binding and action of growth hormone in isolated rat adipocytes

Ionic zinc has been shown to exert a dose-dependent (250-500 microM) stimulation of 125I-human growth hormone specific binding to isolated rat adipocytes. The effect was rapid, being observed in less than 15 min exposure to zinc, and was due to an increased number of available binding sites as determined by Scatchard analysis. The well-known insulin-like effects of both zinc and growth hormone on lipogenesis in this tissue were additive at submaximal doses of each agonist, but zinc did not appear to potentiate growth hormone action. A similar, but smaller effect of zinc on growth hormone specific binding was observed in rabbit liver membranes at lower zinc concentrations (5-100 microM). At higher zinc doses a marked increase in non-specific binding caused a reduction of specific binding in liver membranes. These studies raise the possibility that zinc may be a modulator of growth hormone binding in vivo. Although our initial experiments suggest that this may be independent of an effect on growth hormone action, further studies are required to assess the possibility that zinc's effect at the receptor level may be to increase the sensitivity of tissues to growth hormone, thereby promoting a full manifestation of effects at lower growth hormone concentrations.