Studies on oocyte maturation of the medaka, Oryzias latipes V. On the structure of steroids that induce maturation in vitro

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Abstract
The response of oocytes within isolated follicles (800–950μ in diameter) to various steroids was examined with the teleost fish, Oryzias latipes. Continuous exposure of oocytes, which were removed from ovarian investments 17 hours before predicted germinal vesicle breakdown (GVBD), to C19‐ or C21‐steroids brought about maturation in vitro but never triggered ovulation. The steroids effective in inducing maturation have in common a C = O (or α‐OH) group at 3C and a β‐OH group at 17C in the C19‐steroids, and a C = 0 (or β‐OH) group at 3C and a C = O (or α‐OH) group at 20C in the C21‐steroids, in addition to an Δ4‐ or Δ5‐unsaturated or 5α‐saturated configuration. The orientation of the hydrogen at 5C seems to be critical in determining the ability of a particular steroid to stimulate oocyte maturation.Maturation of oocytes in the ovaries of hypophysectomized females was induced by administering progesterone, but the mature oocytes did not subsequently undergo ovulation. Thus the steroid hormone is capable of inducing oocyte maturation but apparently does not participate directly in the ovulation of Oryzias latipes oocytes.