The effects of different doses of pimozide and [D-Ala6, Pro9-N ethylamide]-LHRH (LHRH-A) on gonadotropin release and ovulation in female goldfish

Abstract

Female goldfish, in late stages of ovarian recrudescence, held at 12 or 20 °C, were injected with a range of dosages of the dopamine antagonist pimozide, at 10, 1, and 0.1 μg/g body weight, to block the endogenous gonadotropin release inhibitory activity of dopamine, and 3 h later were injected with [D-Ala6, Pro9-N ethylamide]-luteinizing hormone-releasing hormone (LHRH-A), at 0.1 μg/g body weight, after which serum gonadotropin levels were determined. The results demonstrate the dose dependency of pimozide in potentiating the activity of LHRH-A. In a second set of experiments, using female goldfish in a preovulatory condition, held at 12 and 20 °C, the changes in serum gonadotropin levels and frequency of ovulation were determined following injection of pimozide, at 1 μg/g body weight, and LHRH-A, at 0.1, 0.01, and 0.001 μg/g body weight. The results demonstrate that pimozide potentiates a dose-dependent response to LHRH-A. The maximum serum GtH levels found in response to the same dosages of pimozide and LHRH-A at 12 and 20 °C were similar; however, the maximum levels occurred earlier at 20 °C (6 h postinjections) than at 12 °C (24 h postinjections). Notably, only the combination of pimozide at 1 μg/g body weight and LHRH-A at 0.1 μg/g body weight, in fish at 20 °C, was highly effective in inducing ovulation.