The Characteristics of hGH Binding to the Liver Macrophages

Summary

Macrophages isolated from female rat liver as well as hepatocytes bind ¹²⁵I-hGH. This study compares the effect of sex of the rat, hypophysectomy (hypox) and preincubation of the cells with oPrl on the binding of ¹²⁵I-hGH to the cells. The percent of ¹²⁵I-hGH bound to the hepatocytes was decreased in cells from hypox female and male rats, and hepatocytes preincubated with oPrl to 0.43, 0.21 and 0.39, respectively, of that observed in hepatocytes from normal female rats. In the hepatocytes from normal female, hypox female, and male rats, hGH was the most effective competitor for ¹²⁵I-hGH binding with an ID₅₀ of 0.73-0.99 nM. The concentration of oPrl, bGH and rGH that produced half-maximal inhibition (ID₅₀) of ¹²⁵I-hGH binding to hepatocytes from female rat liver was 6.3, 100, and 420 nM respectively. In hepatocytes from male and hypox female rats, and hepatocytes preincubated with oPrl, the ID₅₀ for bGH and rGH varied from 2.1 to 15.9nM.

The percent of ¹²⁵I-hGH bound by the macrophages from hypox female and male rats, and macrophages preincubated with oPrl was 0.06, 0.15 and 0.18, respectively, of that bound by macrophages from normal female rat liver. In contrast to hGH binding to the hepatocytes, the ID₅₀ for hGH was 6 to 180-fold greater in macrophages from hypox female and male rats, and macrophages preincubated with oPrl compared to that observed in macrophages from normal female rats. Rat GH was the most effective competitor for ¹²⁵I-hGH binding in the macrophages from the hypox female and male rat liver with ID₅₀ of 5.5 and 85 respectively. The ID₅₀ for oPrl in macrophages from male and hypox female rat liver, and macrophages preincubated with oPrl was greater than 500 nM.

The results suggest that the receptors for hGH on hepatocytes and liver macrophages are affected by the same hormonal control. In contrast to hepatocytes, the residual receptors for hGH in macrophages from hypox female and male rats, and macrophages preincubated with oPrl are not characteristic of those residual somatotropic hormone receptors on hepatocytes from the same animals. In fact, the binding of hGH to the macrophage from hypox and male rats is negligible and therefore the presence of the hGH receptor on the macrophage may be entirely dependent on an intact pituitary in a female rat.

Key-Words

hGH-Binding - Liver Macrophages - Female Rat