SUBSTRATE UTILIZATION AND MATURATION OF CUMULUS CELL-ENCLOSED MOUSE OOCYTES - EVIDENCE THAT PYRUVATE OXIDATION DOES NOT MEDIATE MEIOTIC INDUCTION

This study was performed to address the possible role of pyruvate in m eiotic induction in mouse oocytes. Cumulus cell-enclosed oocytes from primed, immature mite were cultured in 7.5 mu l microdrops under oil f or 9 or 18 h in medium containing 4 mmol hypoxanthine l(-1) plus 0.23 mmol pyruvate l(-1), 1 mmol pyruvate l(-1), or 1 mmol pyruvate l(-1) p lus 5.5 mmol glucose l(-1). When compared with cultures containing 0.2 3 mmol pyruvate l(-1), I mmol pyruvate l(-1) induced germinal vesicle breakdown, and this was preceded by an increase in pyruvate utilizatio n. Addition of glucose prevented both the increase in pyruvate consump tion and the meiotic induction. When different combinations of pyruvat e and glucose were tested on oocyte maturation in microdrop cultures, a high concentration of pyruvate or glucose alone was stimulatory to m aturation. Addition of the complementary energy substrate prevented th e induction of germinal vesicle breakdown and reduced the amount of su bstrate consumption. During spontaneous maturation in vitro, oocyte-cu mulus cell complexes consumed glucose for the first 3 h; however, duri ng the second 3 h period, which followed germinal vesicle breakdown, g lucose consumption decreased and net pyruvate utilization was initiate d. Treatment of hypoxanthine-arrested oocytes with dichloroacetate, an activator of pyruvate dehydrogenase, stimulated pyruvate consumption but had no effect on germinal vesicle breakdown. Although FSH stimulat es meiotic resumption, no changes in pyruvate consumption were observe d in response to this gonadotrophin. Measurement of oxygen consumption by hypoxanthine-treated complexes revealed no effect of high concentr ations of pyruvate on respiration, and FSH treatment resulted in a sup pression of oxygen utilization. These data indicate that, in mouse ooc yte-cumulus cell complexes, pyruvate and glucose can each modulate met abolism of the other substrate, and this can significantly influence m eiotic maturation of the oocyte. In addition, augmentation of pyruvate oxidation does not appear to play a mediating role in meiotic inducti on triggered by energy substrate manipulation or gonadotrophin treatme nt.