BINDING STUDIES OF GROWTH HORMDNE TO RAT LIVER CELLS

Abstract

The interaction of human growth hormone (HGH) with isolated liver cells from normal rats has been studied. Cells prepared with the method described by Berry and Friend were incubated at room temperature with 125I-labeled HGH. Free and cell-bound hormone were separated by filtration or centrifugation. The binding of 125I-HGH to liver cells is a specific, time dependent, saturable and reversible process. At a hormone concentration of 5 × 10−11M, equilibrium of binding is achieved in 120 minutes. The bound labeled HGH is rapidly dissociated by addition of an excess of unlabeled hormone. The specific binding of 125I-HGH is saturable at a hormone concentration of 6 × 10−10M. 1500 molecules of HGH are specifically bound per cell. Native HGH inhibits binding of 125I-HGH to cells; half maximal inhibition occurs at 4 × 10−9M. No significant inactivation or degradation of 125I-HGH or of the specific receptors occurs. Preliminary data indicate that those receptor sites are biologically meaningful.