Growth hormone (GH)-dependent hepatic GH receptors in the Japanese eel, Anguilla japonica: effects of hypophysectomy and GH injection.

Control mechanisms of growth hormone (GH) receptors in the eel liver were examined by following the time course of changes in total (MgCl2-treated membranes) and free (untreated membranes) GH-binding sites after hypophysectomy and replacement therapy with homologous GH. Both total and free binding sites decreased significantly 1 week after hypophysectomy. Scatchard analysis indicated that the reduction in GH receptors was primarily due to a decrease in the number of binding sites, rather than to a change in binding affinity. When recombinant eel GH was injected intramuscularly into hypophysectomized eels (2 micrograms/g body wt), plasma GH concentration increased to a maximal value after 10 hr and decreased to the initial level by 72 hr. Free binding sites decreased to a minimal value 24 hr after the injection and returned to the initial level after 72 hr. The reduction in free binding sites seems to be due to occupation of GH receptors. Total binding sites increased gradually to almost twofold over those of the controls 5 days after the injection, the increase being due to an increase in the binding capacity. GH appears to be importantly involved in inducing and maintaining its own receptors in the eel liver.