A Membrane Receptor Mechanism for Steroid Hormones Reinitiating Meiosis in Xenopus Laevis Oocytes*

There is a membrane progesterone receptor in Xenopus laevis oocytes that undergo meiosis under steroid exposure. Early responses include a decrease of leucine uptake, a decrease of adenylate cyclase and alkaline phosphatase activities, and a decrease of the phosphorylation of a specific p48 protein in the membrane. These results are compatible with a decrease of membrane fluidity brought about by the hormonal message. However the above‐cited effects as well as the Ca 2+ ‐changes are not yet enough well understood to be able to precisely delineate their role in meiosis reinitiation.