Changes in plasma concentrations of gonadotropin, 17β-estradiol, testosterone, and 17α-hydroxy-20β-dihydroprogesterone during spontaneous and brain lesion induced ovulation in goldfish

Abstract

Female goldfish (Carassius auratus) were held at 20–21 °C and ovulation was triggered by radiofrequency lesion of the anterior portion of the nucleus preopticus periventricularis (NPP) as in previous studies. NPP lesions induced a rapid and dramatic increase in blood gonadotropin (GtH) which reached peak levels between 9 and 15 h postlesioning and persisted for at least 48 h postlesioning. Unlike spontaneous ovulation, which is synchronized with photoperiod, NPP lesion-induced ovulation at 20–21 °C occurs 10–14 h postlesioning regardless of the time of day the operation is performed. 17α-hydroxy-20β-dihydroprogesterone, a potent inducer of oocyte final maturation in goldfish, could be detected in plasma of lesioned fish only at 5 h after the operation, Plasma testosterone levels peaked 2.5 h postlesioning (about 10 h prior to ovulation) and tended to decrease at subsequent sampling times. In contrast, peak levels of estradiol were not seen until 15 h postlesioning (several hours after ovulation). Pre- and post-ovulatory samples from spontaneously ovulating fish demonstrated a similar pattern of decreasing testosterone and increasing estradiol.