Cyclic AMP-mediated control of meiosis: effects of progesterone, cholera toxin, and membrane-active drugs in Xenopus laevis oocytes.

Progesterone depressed rapidly (50% at 1 min) and persistently cyclic AMP (cAMP) concentration that had been elevated by cholera toxin in Xenopus laevis oocytes. cAMP remained below 1 pmol per oocyte (mean basal level) for approximately 1 hr and thereafter rose to approximately 120% of control values, while germinal vesicle (nucleus) breakdown did not occur. In the absence of cholera toxin, progesterone treatment for 6 hr maintained cAMP concentration below the basal level (but not lower than 80%), and germinal vesicle breakdown occurred. Experiments in the presence of phosphodiesterase inhibitors suggested that progesterone modulates adenylate cyclase activity. The maturation promoting factor, which is formed after 3-5 hr of progesterone treatment and provokes germinal vesicle breakdown after its injection into untreated oocytes, also decreased cAMP concentration, an observation that may explain its "autoamplification." Nonsteroidal inducers of meiosis reinitiation (e.g., propranolol, methoxyverapamil, mersalyl) diminished the cholera toxin-mediated accumulation of cAMP, in contrast to compounds devoid of meiotic-inducing capacity and antagonist to progesterone action, such as gammexane (an inositol analogue) and 5'-deoxy-S-(2-methylpropyl)-5'-thioadenosine (a methylase inhibitor), that increased the nucleotide level. The fine control, suggested by the effects of small changes in cAMP levels, gives evidence of great sensitivity to a critical determinant governing meiotic cell division.