Metabolism of radiolabeled glucose by mouse oocytes and oocyte-cumulus cell complexes

This study was carried out to examine the metabolism of [1-C-14]-, [6-C-14] -, and [5-H-3]glucose by oocyte-cumulus cell complexes (OCC) and denuded oo cytes (DO) and to test the hypothesis that metabolism of glucose through th e pentose phosphate pathway is associated with meiotic induction. OCC or DO were cultured in hanging drops suspended from the cap of a microfuge tube, with NaOH serving as a frap to collect released (H2O)-H-3 or (CO2)-C-14. P reliminary experiments established that this culture system supports both s pontaneous and ligand-induced meiotic maturation. An initial time course ex periment (1.5-6 h) showed that hypoxanthine-treated OCC from eCG-primed ani mals metabolized glucose principally via glycolysis, with an increase to 2. 7-fold in response to FSH. Though more [1-C-14]glucose was oxidized than [6 -C-14]glucose, its metabolism was about two orders of magnitude less than t hat of [5-H-3]glucose, Also, FSH significantly increased oxidation of [1-C- 14]glucose but not [6-C-14]glucose, indicating a preferential activation of the pentose phosphate pathway. Pyrroline carboxylate, an activator of the pentose phosphate pathway, increased the activity of this pathway to over 2 -fold but failed to affect glucose oxidation through the tricarboxylic acid cycle. Glycolytic metabolism was increased by 25%. The addition of pyruvat e to pyruvate-free medium resulted in significant reduction in the metaboli sm of all three glucose analogues. In OCC retrieved from hCG-injected, prim ed mice and cultured under hormone-free conditions, metabolic responses wer e similar to those in FSH-treated complexes cultured in hypoxanthine, DO me tabolized glucose, but at a much reduced rate when compared to OCC, Pyruvat e reduced the consumption of all three glucose analogues by DO. Pyrroline c arboxylate reduced [5-H-3]glucose metabolism by DO but had little effect on [1-C-14]- and [6-C-14]glucose oxidation. These data demonstrate metabolism of glucose by both DO and OCC, but reveal that cumulus cells are more acti ve than the oocyte in this regard. In addition, induction of maturation by FSH, hCG, or pyrroline carboxylate was accompanied by a significant increas e in the oxidation of [1-C-14]glucose but not [6-C-14]glucose by OCC, suppo rting a proposed role for the pentose phosphate pathway in meiotic inductio n.