cAMP in ovine oocytes: Localization of synthesis and its action on protein synthesis, phosphorylation, and meiosis

Abstract

In the first series of experiments, the source of cAMP in the sheep oocyte was studied. Cholera toxin was shown to be a potent stimulator of cAMP in isolated sheep oocytes, demonstrating the presence of adenyl cyclase. There was no evidence for transmission of cAMP from stimulated myocardial cell monolayers to cumulus‐enclosed oocytes even though the existence of a concentration gradient of cAMP and of intercellular communication were demonstrated. However, gonadotrophin‐stimulated follicle shells were able to induce a rise in the cAMP content of denuded or cumulus‐enclosed oocytes in the same dish, independently of cell contact. Further experiments were designed to study the effects of a cholera toxin‐stimulated rise in cAMP on the maturation of oocytes. When applied to cumulus‐oocyte complexes, cholera toxin did not block germinal vesicle breakdown (GVBD), nor the accompanying changes in protein synthesis and phosphorylation, although there was evidence for a delaying effect. There were, however, indications that the toxin was inducing abnormalities that became gross when the concentration was raised 1 μg/ml. This high concentration of cholera toxin was able to block the maturation of oocytes in intact, gonadotrophin‐treated follicles, although once again abnormalities were evident. We conclude that the role of cAMP in the maturation of the sheep oocyte is different from that proposed in the mouse.