The role of eicosanoids in 17α, 20β-dihydroxy-4-pregnen-3-one-induced ovulation and spawning in Danio rerio

•Tested a 17,20βP bioassay for ovulation and spawning in zebrafish.•Used bioassay framework to study role of eicosanoids in ovulation and spawning.•17,20βP induces ovulation, but not spawning, in solitary female zebrafish.•17,20βP induces spawning in mixed-sex pairs of zebrafish.•COX and LOX metabolites appear to mediate 17,20βP-induced ovulation and spawning.

This study employed a hormone bioassay to characterize the eicosanoids involved in zebrafish ovulation and spawning, in particular the prostaglandin (PG) products of cyclooxygenase (COX) metabolism and the leukotriene (LT) products of lipoxygenase (LOX) metabolism. Exposure to the teleost progestogen 17α, 20β-dihydroxy-4-pregnen-3-one (17,20βP) induced ovulation, but not spawning, in solitary females and both ovulation and spawning in male–female pairs. Transcription of the eicosanoid-synthesizing enzymes cytosolic phospholipase A2 (cPLA2) and COX-2 increased and LTC4 synthase decreased in peri-ovulatory ovaries of 17,20βP-exposed fish. Ovarian PGF2α levels increased post-spawning in 17,20βP-exposed fish, but there was no difference in LTB4 or LTC4. Pre-exposure to cPLA2 or LOX inhibitors reduced 17,20βP-induced ovulation rates, while a COX inhibitor had no effect on ovulation or spawning. Collectively, these findings suggest that eicosanoids, in particular LOX metabolites, mediate 17,20βP-induced ovulation in zebrafish. COX metabolites also appear to be involved in ovulation and spawning but their role remains undefined.