PRECURSORS OF THE PURINE BACKBONE AUGMENT THE INHIBITORY-ACTION OF HYPOXANTHINE AND DIBUTYRYL-CAMP ON MOUSE OOCYTE MATURATION

In this study we have tested the hypothesis that precursors of the pur ine base backbone-glutamine, glycine, aspartic acid, and formate-promo te meiotic arrest when included in medium containing established meiot ic inhibitors and that this occurs in glucose-dependent fashion. An in itial experiment established that in medium supplemented with 4 mM hyp oxanthine and containing no purine precursors, very little meiotic arr est was maintained in cumulus cell-enclosed oocytes after 17-18 hr (90 % germinal vesicle breakdown; GVB). Increasing concentrations of gluco se reduced the maturation percentage such that only 57% had matured at 0.55 mM. The addition of 2 mM glutamine (Gln) alone reduced the matur ation percentage in the absence of glucose (70% GVB), and the further addition of glucose revealed an additive inhibitory effect between the se two supplements. Dose response experiments with Gin, glycine (Gly), aspartic acid and formate showed that in medium supplemented with hyp oxanthine, very little inhibitory action was observed in the absence o f glucose but that upon addition of this hexose, a dramatic decrease i n maturation percentage was observed in the Gin and Gly groups. Result s of experiments using combinations of precursors showed. that when Gi n and Gly were added together, greater augmentation of meiotic arrest maintained by either hypoxanthine or dibutyryl cAMP was achieved in th e presence of glucose than with either amino acid alone. The addition of purine precursors significantly increased the extent of purine nucl eotide production by oocyte-cumulus cell complexes, and this was accen tuated by glucose. It is concluded that the presence of purine precurs ors can augment the meiosis-arresting action of established meiotic in hibitors in glucose-dependent fashion, and that this is due, at least in part, to their incorporation into purine nucleotides via the de nov o synthetic pathway. (C) 1998 Wiley-Liss, Inc.