In vitro effects of 17 alpha-hydroxyprogesterone and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one on final maturation of oocytes at various developmental stages in artificially matured Japanese eel Anguilla japonica

In vitro effects of 17 alpha-hydroxyprogesterone and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (DHP) on germinal vesicle breakdown (GVBD) of oocytes at various developmental stages were examined in artificially matured Japanese ed. Neither 17 alpha-hydroxyprogesterone nor DHP induced GVBD in oocytes at a tertiary yolk stage ranging from 600-700 mu m in diameter, Oocytes at a migratory nucleus stage ranging from 700 to 800 mu m in diameter underwent GVBD in response to 17 alpha-hydroxyprogesterone and DHP at concentrations of 10 and 100 ng/ml. Oocytes over 800 mu m in diameter became more sensitive to the steroids. These results suggest that oocytes acquired the ability to respond to the maturation-inducing steroid at the migratory nucleus stage. Also, oocyte diameter and its microscopic features can be utilized as a reliable indicator of the induced maturation and ovulation by the injection of the steroids.