HORMONAL-REGULATION OF THE FEMALE ENRICHED GH RECEPTOR-BINDING PROTEIN MESSENGER-RNA IN RAT-LIVER

At least two classes of mRNA for the GH receptor (GHR) and GH binding protein (GH BP) with different 5' untranslated first exons exist in the rat. One such class, the GHR(1) is predominantly expressed in the liver of female rats. The hepatic expression of the GHR(1) mRNA in normal and hypophysectomized rats of both sexes was studied by employing an RNase protection/solution hybridization assay. Normal females expressed 10-fold more GHR(1) mRNA than males, hypophysectomy of female rats decreased the GHR(1) level to that observed in male rats. Continuous GH treatment of hypophysectomized male and female rats for 6 days increased the expression of GHR(1) mRNA to levels found in normal females, whereas intermittent GH treatment was without effect. Bovine GH (bGH) induced the GHR(1) expression in a time- and dose-dependent manner in primary cultures of adult rat hepatocytes as determined by solution hybridization. Maximal induction was achieved after 72 h of treatment with 50 ng bGH/ml medium. Female enriched expression of receptor and binding protein mRNAs raises the possibility that they participate in determining the ability of the liver to respond differently to the male and female GH secretory patterns. Our in vitro model utilizing cultures of primary adult rat hepatocytes could be used to address this issue as well as explore a hormonal interplay in regulation of GHR(1) expression.