In Vitro Effects of 17α-hydroxyprogesterone and 17α, 20β-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 α-hydroxyprogesterone and 17 α, 20 β-dihydroxy-4-pregnen-3-one (DHP) on germinal vesicle breakdown (GVBD) of oocytes at various developmental stages were examined in artificially matured Japanese eel. Neither 17 α-hydroxyprogesterone nor DHP induced GVBD in oocytes at a tertiary yolk stage ranging from 600-700 μm in diameter. Oocytes at a migratory nucleus stage ranging from 700 to 800 μm in diameter underwent GVBD in response to 17 α-hydroxyprogesterone and DHP at concentrations of 10 and 100 ng/ml. Oocytes over 800 μm 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.