Differential secretory rhythm of growth hormone controls the number of hepatic epidermal growth factor receptors in the rat

The effect of human GH (hGH) on hepatic epidermal growth factor (EGF) receptors in the rat was investigated. Continuous administration of hGH through an osmotic minipump, mimicking the female pattern of GH secretion, to normal male rats reduced the binding of 125I-labelled EGF to hepatic membranes to the normal female levels. The same treatment of hGH applied to hypophysectomized males had no apparent effect on EGF binding. Intermittent s.c. administration of hGH twice a day (every 12 h), mimicking the male pattern of GH secretion, to hypophysectomized male and/or normal female rats, caused a significant increase in EGF binding to the levels of normal male rats. Scatchard analysis of the binding data clearly showed that the change in EGF binding was due to a change in the number of EGF receptors. The results on the affinity labelling and phosphorylation of EGF receptors were in good agreement with those showing differences in the number of EGF receptors among the experimental groups. These results indicate that the number of hepatic EGF receptors in the rat is regulated by the differential secretory rhythm of pituitary GH between the sexes.