Effect of food and GH on the binding of 125I-somatomedin A to the membranes of rat lung and kidney.

Studies were undertaken to examine the relationship between serum levels of somatomedin A and its binding sites in the lung and kidney of rats. After three days of fasting, serum levels of somatomedin A decreased, accompanied by increases of 17.5% and 21.4% in binding to the plasma membranes from lung and kidney, respectively. After two days of refeeding, this binding decreased with the increase in the serum level of somatomedin A. There was observed a negative correlation between the serum level of somatomedin A and the percentage of labelled somatomedin A bound to the membranes. These observations suggest that somatomedin down-regulates its own receptor under these conditions. A similar regulatory mechanism was not observed with either hypophysectomized- or GH-treated rats.