Induction of germinal vesicle breakdown in Xenopus laevis oocytes: synergistic action of progesterone and insulin

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Abstract
Progesterone is the hormone that reinitiates the meiotic division of amphibian oocytes and insulin and insulin-like growth factors are also active on defolliculated oocytes in vitro. We have studied Xenopus laevis oocytes (stage 5–6) of different hormonal sensitivities, obtained from unstimulated and from human chorionic gonadotrophin-stimulated females. Some oocytes from unstimulated females were also precultured with a subthreshold level of progesterone. A dose-dependent potentiating effect of the action of progesterone was observed with insulin, and this was particularly remarkable in low-sensitivity oocytes. Since in the presence of insulin, the optimally effective concentration of progesterone was much reduced (as an example from 1 μmol/l to 50 nmol/l), it is suggested that an insulin-like growth factor may play a physiological role in the reinitiation of meiosis in ovaries. J. Endocr. (1984) 101, 7–12

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