Effect of L-dopa administration on insulin binding: possible role of growth hormone in regulation of insulin receptor affinity.

Abstract

We have investigated changes in insulin binding to erythrocytes in response to the oral administration of 500 mg of L-Dopa in ten healthy subjects. L-Dopa administration increases insulin binding from 5.18 +/- 0.14% (mean +/- SEM) to 6.18 +/- 0.34% (P less than 0.05) with concomitant increase in basal plasma growth hormone from 1.3 +/- 0.1 ng/ml to 14.4 +/- 4.8 ng/ml (P less than 0.05). The increase in insulin binding is due to increase in affinity of insulin receptor without changes in the number of insulin receptors. The plasma insulin and glucose did not show significant changes after L-Dopa administration. Direct incubation of L-Dopa with erythrocytes did not affect insulin binding to the cells. These results suggest that growth hormone may directly or indirectly induce acute alteration in affinity of insulin receptors on erythrocytes.