GLUCOSE-UTILIZATION DURING GONADOTROPIN-INDUCED MEIOTIC MATURATION INCUMULUS CELL-ENCLOSED MOUSE OOCYTES

Earlier work from this laboratory has determined that glucose plays an important role in the mechanisms regulating meiotic maturation in mam malian oocytes. In the current study, we have further explored the rol e of glucose in hormone-induced germinal vesicle breakdown (GVB) in an effort to better understand how glucose utilization and metabolism re late to the control of meiotic maturation in mouse cumulus cell-enclos ed oocytes (CEO). When CEO were cultured in medium containing 4 mM hyp oxanthine (to maintain meiotic arrest), 5.5 mM glucose, and 0.23 mM py ruvate, follicle-stimulating hormone (FSH) stimulated lactate accumula tion in a time-dependent manner. Addition of 2-deoxyglucose (2-DG) to the medium at various times after the initiation of culture resulted i n rapid termination of lactate production and suppression of FSH-induc ed GVB scored after 18 hr of culture, the effectiveness diminishing th e longer the delay before addition of 2-DG. By 8 hr, addition of 2-DG was without effect on GVB. Similar effects were seen when FSH-treated CEO were washed free of glucose. In a 2-DG dose-response experiment, g onadotropin-induced lactate production was prevented, but this inhibit ion did not necessarily prevent GVB. The activities of six metabolic e nzymes were measured in extracts of freshly isolated complexes, and in order of increasing activity were: hexokinase, 6-phosphogluconate deh ydrogenase, glucosed-phosphate dehydrogenase, phosphofructokinase, lac tate dehydrogenase, and pyruvate kinase. Of the six enzymes examined, only hexokinase activity was increased in CEO exposed to FSH. CEO were cultured in microdrops in the presence or absence of FSH, and aliquot s from the same microdrop were assayed for glucose, lactate, and pyruv ate. In response to FSH, utilization of glucose in microdrop cultures by CEO was markedly increased and was accompanied by comparable lactat e production and limited pyruvate production. Cycloheximide and oc-ama nitin both blocked FSH-induced oocyte maturation, but only cycloheximi de prevented the increase in hexokinase activity and glucose consumpti on, These data suggest that hexokinase is an important rate-limiting e nzyme for glucose utilization that is under translational control and participates in the mechanisms controlling the reinitiation of meiosis . However, stimulation of glycolytic activity does not appear to be a necessary concomitant for meiotic induction. (C) 1996 Wiley-Liss, Inc.