Comparison of hGH Binding to Isolated Rat Liver Macrophages and Hepatocytes

Summary

The binding characteristics of hGH to rat liver macrophages (Kupfer cells) and hepatocytes have been compared to determine the role of each in the binding of hGH to liver tissue. The time course of binding, displacement of bound ¹²⁵I-hGH and effect of pH on binding was qualitatively similar for macrophages and hepatocytes. Since the macrophage isolation depends upon their phagocytosis of iron particles, we determined that exposure of the isolated hepatocytes to the iron did not affect their binding of ¹²⁵I-hGH.

The relative capacity of the macrophage preparations was two-fold less than the hepatocyte preparations. This indicated that the hepatocyte is responsible for the majority of the hGH binding by the liver. In contrast, the cell surface concentration of the hGH receptor on the macrophage is greater than the hepatocyte.

Ovine prolactin and hPrl were equipotent in competing for the binding of ¹²⁵I-hGH to the macrophage receptor while only oPrl was significantly competitive in the hepatocytes. Bovine GH and hPI exhibited minimal interaction for ¹²⁵I-hGH binding in both cell preparations.

We conclude that even though significant differences in ¹²⁵I-hGH binding do exist between hepatocytes and liver macrophages, the macrophages contribute significantly to hGH binding by hepatic tissue. The demonstration of somatomedin production by fibroblasts in culture suggest a possible role of the hepatic macrophage in GH responsiveness of the liver.

Key-Words:

hGH Binding - Macrophages - Hepatocytes - Rat Liver