| Abstract: | Progesterone appears to be the physiological inducer of meiosis in amphibian oocytes. In Rana pipiens, dl-propranolol mimics the action of progesterone and both agents have a common action in producing a rapid [45Ca] efflux and a fall in intracellular cAMP followed by nuclear breakdown. Comparison of the rate of hydrolysis of injected [3H]-cAMP and of the conversion of injected [3H]-ATP to [3H]-cAMP followed exposure to meiotic inducers and inhibitors indicates that adenylate cyclase and not phosphodiesterase is the rate-limiting step in regulating [cAMP]i in the oocyte. The results suggest that progesterone initiates the resumption of the meiotic divisions by down-regulation of membrane adenylate cyclase, possibly via Ca2+ release from specific membrane sites. |
