ROLE OF CYCLIC AMP IN OOCYTE MATURATION AND GLYCOLYSIS IN THE PRE-OVULATORY RAT FOLLICLE

Abstract

The role of cyclic[c]AMP in the stimulatory action of LH [luteinizing hormone] on the resumption of oocyte meiosis (oocyte maturation) and follicular glycolysis was examined. Follicular development was induced in immature rats by a single injection of pregnant mares'' serum gonadotropin. Pre-ovulatory follicles were extirpated on the day before ovulation and incubated in a chemically defined medium for 4-10 h. The follicle-enclosed oocytes remained in the dictyate stage when incubated in hormone-free medium but in the presence of LH oocyte maturation was induced. When cAMP or butyryl derivatives of cAMP were added to the incubation medium no effect on the oocyte was seen. These nucleotides prevented the stimulatory action of LH on the oocytes. The phosphodiesterase inhibitors theophylline and IBMX [3-isobutyl-1-methylxanthine] had similar effects as cAMP on oocyte maturation, causing a reversible blockage of the LH effect. When 8-Br-cAMP and the phosphodiesterase inhibitor ICI 63.197 [2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-5-triasolo(1,5-a)pyrimidine] were tested, both had inherent stimulatory effects on oocyte maturation at certain concentrations. Pre-incubation of the follicles in a high concentration of dibutyryl cAMP followed by transfer to plain medium resulted in oocyte maturation. Follicular lactate production was stimulated by all cyclic nucleotide derivatives tested, except cAMP, and by IBMX and ICI 63.197. There was no reduction by these agents of the stimulatory effect of LH on lactate production. A model to explain the role of cAMP in oocyte maturation is presented.