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

germinal vesicle breakdown (GVBD) of oocytes at various developmental stages were examined in arti ficially matured Japanese eel. Neither 17ƒ¿-hydroxyprogesterone nor DHP induced GVBD in oocytes at a tertiary yolk stage ranging from 600-700ƒÊm in diameter. Oocytes at a migratory nucleus stage rang ing from 700 to 800ƒÊm in diameter underwent GVBD in response to 17ƒ¿-hydroxyprogesterone and DHP at concentrations of 10 and 100 ng/ml. Oocytes over 800ƒÊm in diameter became more sensitive to the steroids. These results suggest that oocytes acquired the ability to respond to the maturation-in ducing 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.

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