Effect of insulin on meiosis reinitiation induced in vitro by three progestogens in oocytes of the goldfish (Carassius auratus).

Three progestogens were tested for their ability to elicit meiosis reinitiation as evidenced by germinal vesicle dissolution (GVD) in goldfish (Carassius auratus) follicle-enclosed oocytes in vitro. In two independent experiments 17 alpha-20 beta-dihydroxyprogesterone (DHP) was most active followed in turn by 17 alpha-hydroxyprogesterone (HP) and progesterone (P). Values of the effective dose for a 50% response for GVD induced by P and HP were significantly reduced by the addition of Na-insulin, however, insulin had no significant effect on DHP incubates. Meiotogenic activity was potentiated by Na-insulin in the following heirarchy: P greater than HP greater than DHP. These results indicate that insulin, which had little meiotogenic activity alone, was capable of differentially enhancing progestogen activity in this system. The mechanism by which Na-insulin augments progestogen GVD-inducing activity is unknown, but may include decrease of progestogen degradation, increase in progestogen biosynthesis, and direct insulin effects on the oocyte. The results suggest that insulin may play a physiological role in goldfish oocyte meiosis reinitiation by enhancing the activity of certain progestogens, which by themselves are not potent meiotogens.