Mechanisms regulating ovarian cycle in the toad Bufo bufo bufo (L.): Role of presence of second growth phase oocytes in controlling recruitment from pool of first growth phase oocytes

Studies have been made on the effects of injections of human chorionic gonadotropin (HCG) on the ovarics of adult-sized intact or hypophysectomized female toads in the fall. The effects of HCG treatment varied with the state of the ovaries. In toads with ovaries that did not contain oocytes in the second growth phase (SGP). either because the toads were immature or because the SGP oocytes had beconne atretic, daily injections of 30 IU HCG per 100 g body weight induced first growth phase (FGP) oocytes to euter the SGP in numbers that produeed normal-sized populations of SGP oocytes. In toads with ovaries that did contain populations of SGP oocytes the injections of HCG did not induce vitellogenie growth in FGP oocytes, but they maintained the existing populations of SGP oocytes in hypophysectomized toads. It is suggested that the mechanisms that regulate influx of FGP oocytes to the gonadotropin-dependent growth phase are mainly to be found within the ovary itself.