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R. Sridaran1 *, G.K. Bhat1 , V.B. Mahesh2 *
Department of Physiology, Morehouse School of Medicine, Atlanta, GA 1
Department of Physiology and Endocrinology, Medical College of Georgia, Augusta, GA 2
We have demonstrated that administration of a gonadotropin-releasing hormone (GnRH) agonist results in apoptosis and suppression of steroidogenesis in the corpus luteum (CL) thus leading to termination of pregnancy in rats. However, there has been no clear demonstration of the production of GnRH in the ovary or a clear physiological role for the peptide. The purpose of this study was to determine the presence of endogenous GnRH and bradykinin in the CL by RT-PCR and/or immunohistochemistry and measure changes in them as pregnancy advances in the rat and to determine if there is an inverse correlation between the levels of GnRH and/or bradykinin in CL and serum progesterone (P) levels during parturition. Pregnant rats were killed on days 8, 22, and 23 (after parturition) and the serum, CL and ovaries were saved. Our results indicate that (i) GnRH mRNA was present in the ovary/CL on all 3 days; (ii) while the levels of GnRH mRNA in the CL were highest the levels of serum P were lowest on days 22 and 23 of pregnancy; (iii) RT-PCR fragment obtained from the ovary/CL was found on sequencing to be identical to hypothalamic GnRH sequence; the expression of these proteins in the ovary appears to be more intense than in the CL alone indicating other components of the ovary might express these proteins; and (iv) the data obtained by using immunohistochemical analysis of the ovaries suggest that the highest levels of GnRH and bradykinin ligands were present in the CL on days 22 and 23 compared to day 8. Thus, we have demonstrated, for the first time, the presence of GnRH and bradykinin in the ovary/CL of the rat with increased levels on days 22 and 23 of pregnancy compared to day 8 and further demonstrated an inverse correlation between the levels of GnRH and bradykinin in CL and serum P levels during parturition. (Supported by grants NIH SO6-GM08248 and NASA NAG9-963 to RS).
This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.