Oocyte storage affects the kinetics of insulin-induced GVBD in Xenopus laevis oocytes

Xenopus laevis oocytes underwent meiotic maturation in response to progesterone or insulin stimulation. However, the kinetics of the oocytes' response to the steroid was much faster than the response induced by insulin even under saturating hormone concentrations. This time differential was seen in oocytes that were stimulated with either hormone shortly after they were isolated from the animal. On the contrary, if oocytes were first cultured in MBS medium for 12-14 hours and then treated with either hormone, the oocytes responded to insulin and progesterone with similar kinetics. This result was not due to the ionic strength, potassium concentration or pH of the medium. The effect of storage in MBS was ligand specific for insulin. The extra 12-14 hours in MBS medium had no effect on the oocytes' response to progesterone.