A major goal of my research program is to identify molecules and metabolic pathways that participate in the control of oocyte maturation in mammals. The current proposal will test the idea that modulation of purine metabolism has direct influence on the mechanisms controlling meiotic maturation and that glucose metabolism plays an important role in this control. Purines and their associated metabolic pathways have been implicated as important participants in the mechanisms controlling meiotic maturation. Results of experiments conducted during the current grant period have led to the hypothesis that hypoxanthine maintains meiotic arrest through a cooperative interaction with the purine de novo nucleotide-generating pathways. We have also investigated the involvement of different energy sources in oocyte maturation and have determined that the uptake and metabolism of glucose is required for gonadotropin-induced germinal vesicle breakdown in meiotically arrested cumulus cell-enclosed oocytes in vitro. Further preliminary work suggests that the positive action of gonadotropins may be mediated by the pentose phosphate pathway (PPP) but not glycolysis. We hypothesize that metabolism of glucose through the PP mediates the maturation-inducing effects of follicle-stimulating hormone (FSH) by its effects on purine metabolism. Phosphoribosylpyrophosphate, a compound whose levels rise with increased PPP activity, can serve as an important link between carbohydrate use as a model system the oocyte-cumulus cell complex isolated from immature mice that were primed 48th with pregnant mare serum gonadotropin. Part I will address the effects of FSH on both purine and glucose metabolism in the oocyte-cumulus cell complex as it relates to the meiotic status of the oocyte. By using radiolabeled purines, purine precursors and glucose, we will determine via biochemical assays and HPLC address analyses what metabolic changes occur prior, to and during, FSH-induced meiotic maturation. Part II will address how alteration of specific intermediary steps of the purine metabolic pathways affects other metabolic steps as well as the control of meiotic arrest. Attention will be focused on de novo purine synthesis, the purine salvage pathway, and the nucleoside phosphorylating pathways (ie, adenosine to ATP and guanosine to GTP). In all of these experiments the site of action will be determined by analyzing the oocyte and cumulus cells separately. The proposed experiments will help delineate specific purine metabolic pathways involved in the maintenance of meiotic arrest and in FSH-induced maturation and will help define the role of carbohydrate metabolism in these processes. These results will have important implications for both fertility and contraception, since each is affected by the ability of the oocyte to successfully initiate and complete meiotic maturation. The data will also benefit the development of in vitro systems where either meiotic arrest or completion of meiotic maturation is the desired endpoint.
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