Gonadotropin-induced changes in steroid production by ovaries of the common careCyprinus carnio L. around the time of ovulation

Ovarian fragments from both primed (gonadotrophin treated) and unprimed female carp were incubated either with or without carp hypophysial homogenate and steroid hormone production measured. In incubations without hypophysial homogenate, production of all the steroids measured was either very low or nondetectable and there was no significant difference between tissue from primed and unprimed fish. In the presence of carp hypophysial homogenate a very significant increase in production of testosterone, 17-hydroxyprogesterone and testosterone glucuronide was observed, but there was no significant difference between primed and unprimed fish. 17,20-Dihydroxy-4-pregnen-3-one (17,20P) was not stimulated by carp hypophysial homogenatein vitro in ovaries from unprimed fish, but a very significant increase in production of this hormone was observed in tissue from fish which had received a priming dose of pituitary hormone. It is suggested that the priming dose of pituitary extract used in the normal hypophysation procedure to induce ovulation in teleosts initiates the potential for synthesis of 17,20P in response to later gonadotrophin challenge, and that this initiation may be related to the migration of the germinal vesicle.A preliminary account of these results was presented at the Fish Culture Conference, Barcelona, August 1985 (Kime and Bieniarz 1985).