The goals of this project are evaluate the roles of the sexually differentiated pituitary growth hormone secretory pattern (GHSP), and of other hormones, in the regulation of multiple hepatic genes in the rat, and to clone cDNAs and genomic genes for hepatic mRNAs regulated by the GHSP. This will constitute a major step towards the elucidation of the molecular mechanism(s) of growth hormone action in the liver. The GHSP is distinguished by a highly regular pulsatile rhythm in males, and a more continuous, irregular pattern in females. Several sex-dependent hepatic gene products are regulated by the sexually differentiated GHSP, including two isozymes of cytochrome P-450 (h and i) for which I have cloned cDNAs. Various lines of evidence indicate that although the GHSP has a major role in regulation of these function, other hormones also control the expression of at least some of them.
One specific aim of this project is to evaluate the relative roles of the GHSP and other hormones in regulation of sexually differentiated hepatic gene expression, using P-450h and i as a model. The roles of glucocorticoids and thyroid hormones will be investigated in vivo by administering them to hypophysectomized rats, alone or in combination with growth hormone. The molecular level at which these hormones act will be investigated by measuring hormone effects on the hepatic proteins, their mRNAs, and the rates of nuclear transcription of their genes. Similarly, the role of insulin will be evaluated using a streptozotocin diabetes model. The modulation of P-450h and i during acute inflammatory stress, and the humoral factors involved, will also be examined. Another aim is to clone cDNAs and genomic genes for multiple hepatic GHSP-regulated mRNAs using a hybridization-subtraction method to obtain cDNA libraries and probes enriched for such sequences. The possibility that P- 450 isozyme DEa is GHSP-regulated will be studied by purifying it by a published method, preparing specific antibodies to it, and by cloning its cDNA. It is anticipated that the cloned GHSP- responsive genes and their 5'-flanking regions will be valuable and essential tools in the gaining a better understanding of the mechanism of action of this important hormone, and of peptide hormones in general.
