Induction and Inhibition of Meiotic Maturation in Follicle-enclosed Mouse Oocytes by Forskolin. (meiotic maturation/luteinizing hormone/forskolin/cAMP/mouse oocyte)

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Abstract
A continuous exposure of follicle-enclosed mouse oocytes to ovine luteinizing hormone (LH, 10 .mu.g/ml) in vitro resulted in a 3-fold elevation of cAMP levels in the follicle cells, but not the oocytes, with subsequent oocyte maturation. When follicle-enclosed oocytes were exposed to forskolin (0.01-10 .mu.M) for 2 hr and then incubated in forskolin-free medium (transient exposure group), oocytes underwent germinal vesicle breakdown in a dose-dependent manner. In contrast, a continuous exposure of the follicles to forskolin (10 .mu.M) for up to 10 hr failed to induce resumption of meiosis. Follicle cell cAMP levels increased within 2 hr after the initial exposure to forskolin, and thereafter decreased rapidly regardless of whether forskolin treatment was transient or continuous. A similar transient increase in oocyte cAMP levels was observed after transient or continuous treatment with forskolin. It was evident, however, that at any time examined oocyte cAMP levels were consistently higher in the continuous exposure group than in the transient exposure group. Furthermore, a continuous exposure to forskolin also blocked LH-induced meiotic maturation. These findings suggest that elevated levels of cAMP in the oocyte block meiotic maturation in mouse oocytes. The present results further suggest that an increase in follicle cell cAMP levels is essential to the LH-induced meiotic maturation.