Release of 13, 14-Dihydro-15-Keto-Prostaglandin F_2α, a Sex Pheromone, to Water by Cobitid Loach Following Ovulatory Stimulation

Abstract

The time course change of 13, 14-dihydro-15-keto-prostaglandin F_2α levels in holding waters of the cobitid loach, Misgurnus anguillicaudatus was studied during the ovulatory process initiated by an intraperitoneal injection of human chorionic gonadotropin (hCG). The control fish were injected with Ringer's solution. The 13, 14-dihydro-metabolite contents in the holding water were analyzed by high pressure liquid chromatography at 4 hour-intervals for 16 hours after the injections. In the non-ovulated status, levels of the 13, 14-dihydro-metabolite were only barely detectable in the holding water even in the hCG-injected females. When the hCG-treated females ovulated, the release of the 13, 14-dihydro-metabolite reached maximum levels ranging from 6.71 to 14.38 μg/fish, tending to decrease thereafter. Levels of the 13, 14-dihydro-metabolite were barely detectable in the holding water of the control fish through the experiment. Levels of prostaglandin F_2α were also monitored and although individual release rates varied, a similar trend in release pattern was observed. Thus, the present results clearly show that in synchrony with ovulation, 13, 14-dihydro-15-keto-prostaglandin F_2α which would be one of the postovulatory sex pheromones, was discharged into the environmental water by female loach.