Effect of Follicle-stimulating Hormone on Cyclic Adenosine Monophosphate Level and on Meiotic Maturation in Mouse Cumulus Cell-enclosed Oocytes Cultured in Vitro1

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Abstract
We have reported that in vitro treatment with follicle-stimulating hormone (FSH) delays by about 3 h spontaneous meiotic resumption in cumulus cell-enclosed mouse oocytes. In the present paper we show that the temporary meiotic block is accompanied by a transient increase of cAMP concentration in the oocyte. In cumulus cell-oocyte complexes stimulated with 1 μg/ml FSH, cAMP significantly increases within 1 h both in the whole complex (from a basal value of 1.9 ± 0.2 to 169 ± 13 fmol) and in the enclosed oocyte (from 0.9 ± 0.2 to 2.4 ± 0.2 fmol), then progressively decreases to basal values. Stimulation by FSH does not cause any cAMP increase in denuded oocytes. As the concentration of cAMP in the cells decreases, the percentage of oocytes escaping the meiotic block imposed by FSH increases. If the complexes are cultured in the presence of 1 μg/m1 FSH plus 1 mM isobutyl-1-methylxanthine (IBMX), cAMP concentration increases approximately 250-fold in the complex, and 10-fold in the enclosed oocyte; the level of cAMP in the oocyte drops very rapidly (50% degradation in less than 2 min) if the oocyte is then transferred to IBMX-free medium. The data are discussed in terms of the possible role of cAMP transfer from cumulus cells to the oocyte in the regulation of meiotic progression in mouse oocytes.