THE PARTICIPATION OF ENERGY SUBSTRATES IN THE CONTROL OF MEIOTIC MATURATION IN MURINE OOCYTES

In this study we have examined the effects of various energy substrate combinations on both the maintenance of meiotic arrest and follicle-s timulating hormone (FSH)-induced germinal vesicle breakdown (GVB) in i solated mouse oocytes treated with 4 mM hypoxanthine (HX). When cumulu s cell-enclosed oocytes were cultured in HX minus glucose, the additio n of pyruvate dose-dependently sustained oocyte viability and induced GVB (from 25% GVB at 0 mM pyruvate to 98% GVB at 1 mM pyruvate). FSH h ad a limited stimulatory effect at all pyruvate concentrations. Oxaloa cetate, but no other intermediates of the tricarboxylic acid (TCA) cyc le, mimicked the action of pyruvate on viability and GVB. Lactate alon e induced maturation in the absence of pyruvate but required NAD for t his effect when the medium included pyruvate. Of two TCA cycle inhibit ors tested, malonate had no effect on pyruvate-induced GVB, and fluoro acetate was inhibitory only at the highest concentration (10 mM). Pyru vate, oxaloacetate, and lactate also stimulated maturation in denuded oocytes. Adding glucose back to the medium produced an inhibitory effe ct on meiosis in cumulus cell-enclosed oocytes up to a concentration o f 23 mM and was associated with increases in ATP. Exposure to the glyc olytic inhibitor, iodoacetate, eliminated both the meiotic arrest and ATP production mediated by glucose. High concentrations of glucose (11 1 mM) proved stimulatory to oocyte maturation. Glucose had no effect o n denuded oocytes. FSH-induced maturation was dependent upon the prese nce of glucose but was not causally related to increases in lactate pr oduction. In addition, raising the pyruvate concentration 10-fold did not overcome the meiotic block. Coculture of denuded oocytes with diss ociated cumulus cells, but not intact oocyte-cumulus cell complexes, s timulated GVB in HX-containing medium when glucose was added. However, both the cumulus cells and the complexes produced an increase in pyru vate production, indicating that the effect of the dissociated cumulus cells was not due principally to secretion of this carbohydrate into the culture medium. This study has demonstrated the importance of ener gy substrates in the meiotic response of oocytes in culture. Evidence failed to support a role for increased TCA cycle activity in the stimu latory action of pyruvate. The inhibitory effect of glucose is the res ult of glycolytic activity that produces increased levels of ATP, but production of ATP and glycolytic intermediates does not appear to be t he mechanism whereby glucose mediates a stimulatory action on meiosis, either in response to high glucose levels or FSH treatment. Other ave nues of glucose metabolism or interaction may be responsible for this effect. (C) 1994 Academic Press, Inc.