Induction of Lactogenic Receptors II. Studies on the Liver of Hypophysectomized Male Rats and on Rats Bearing a Growth Hormone Secreting Tumor

Abstract

The role of growth hormone (GH), as well as pro-lactin and ACTH, in the induction of the PRL receptor was investigated both in hypophysectomized male rat livers and in the livers of male rats bearing a GH secreting tumor. After 7 days of s.c. injections, specific binding (% SB) of PRL in controls and rats treated with oPRL, hGH, ACTH, hCG, estradiol (E₂), or testosterone (T) was approximately 1%. Treatment with oPRL plus ACTH increased SB to 4%; adding E₂ to this combination produced a further increase to 8%, whereas the addition of T decreased hepatic binding to 1%. Combination of hGH with ACTH was most effective, giving a SB of 33%, which is similar to that observed in the liver of rats bearing a GH secreting tumor (36%). These studies suggest that GH acts synergistic-ally with PRL and/or ACTH to increase lactogenic binding sites in the male rat liver and that sex steroids have a modulating effect on this action.