FORSKOLIN INCREASES cAMP AND INHIBITS PROGESTERONE INDUCED MEIOSIS REINITIATION IN XENOPUS LAEVIS OOCYTES

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Abstract
The diterpene, forskolin, is a potent and reversible inhibitor of progesterone-induced meiosis in Xenopus laevis oocytes (ED50 of inhibition ∼ 3 μM). Forskolin alone increases cAMP concentration in oocytes, but, unlike with cholera toxin treatment, there is no lag phase, and reversibility is obtained by washing the cells. Progesterone decreases the forskolin effect on cAMP accumulation, but cAMP concentration remains above the level observed in oocytes treated with progesterone alone. The data corroborate the previously-established antagonistic effect of cAMP on progesterone-induced meiosis. Preliminary experiments in the presence of a phosphodiesterase inhibitor suggest that, as in other biological systems, forskolin is an activator of adenylate cyclase in Xenopus laevis oocytes. Contrary to what is observed when forskolin is present in the incubation medium, no effect of the diterpene is recorded after its injection into oocytes, evoking a site of action at the external side of the membrane.

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