Hormonal regulation of growth hormone binding and responsiveness in adipose tissue and adipocytes of hypophysectomized rats.

The hormonal regulation of GH binding and the effects of GH on glucose metabolism were studied in hypophysectomized rats. Male rats (130-140 g) were hypophysectomized and on the day after the operation treatment with one or a combination of two hormones was started and continued for 7 days. The different hormonal treatments were cortisone acetate, insulin, insulin plus cortisone acetate, thyroxine, thyroxine plus cortisone acetate and GH. Glucose metabolism was studied by determining the production of CO2 from [14C]glucose in epididymal fat pads and adipocytes and the incorporation of [14C]glucose into lipids in adipocytes. Binding of GH was measured in cell aliquots using 125I-labelled human GH. In hypophysectomized control animals, GH binding was decreased to approximately 25% of the binding observed in adipocytes of normal rats. Insulin treatment increased GH binding by approximately 100% and the response to GH was markedly increased. Similar effects were achieved by thyroxine treatment. Basal levels of glucose oxidation were markedly decreased after hypophysectomy but were increased towards normal by insulin or thyroxine treatment. Neither cortisone nor GH treatment had any effect on GH binding or glucose metabolism. The results show that insulin and thyroxine may be important for the GH receptor and the insulin-like effect of GH in adipocytes.