The long-term objective of this research is to determine the neuroendocrine mechanisms by which estrogen (E) and progesterone (P) control the preovulatory surge release of luteinizing hormone (LH). Although LHRH neurons do not concentrate E or P, they act as the final common pathway by which multiple neurotransmitter systems translate information from the ovary into signals which modulate LH release. The ovarian hormone modulation of LHRH release has been studied intensively; however, little is known about the effects of E and P on LHRH biosynthesis. This information has been previously unattainable, largely because the LHRH gene had not been described, and the structure of LHRH prohormone was unknown. The present studies will use newly-developed methods and probes specific for LHRH prohormone and LHRH mRNA to determine whether LHRH biosynthesis is increased around the time of the LH surge release. The working hypothesis is that ovarian hormones stimulate de novo synthesis of LHRH before the LH surge and that LHRH hypersecretion during the surge is accompanied by elevated LHRH gene transcription. The studies proposed to test this hypothesis will also provide information regarding the relationships among LHRH transcription, steady-state LHRH mRNA levels, and LHRH translation. This information will help explain apparent discrepancies in the literature regarding the effect of E on LHRH mRNA levels. To obtain this information, we will evaluate the effects of ovarian steroids on changes in LHRH gene transcription (using nuclear run-on assays and measurements of nuclear transcripts of LHRH mRNA), cellular levels of LHRH mRNA (using in situ hybridization histochemistry and solution hybridization) and LHRH mRNA translation (by measuring ratios of LHRH prohormone and decapeptide throughout the LHRH neuronal system. These studies will provide important new information on the mechanisms by which E and P act in the hypothalamus to modulate LH release. Such information is important to the development of treatments for infertility, delayed puberty and menopausal symptoms, as well as for the development of better and safer contraceptives.
