Effects of polyunsaturated fatty acids and prostaglandins on oocyte maturation in a marine teleost, the European sea bass (Dicentrarchus labrax)

The effects of the polyunsaturated fatty acids (PUFAs), arachidonic acid (A A), eicosapentaenoic acid (FPA), docosahexaenoic acid (DHA), and prostaglan dins (PGs) on oocyte maturation were investigated in a marine teleost, the sea bass (Dicentrarchus labrax). Follicle-enclosed postvitellogenic, preovu latory oocytes were cultured in vitro and maturation was verified by assess ing volume increase, lipid droplet coalescence, yolk clarification, and ger minal vesicle migration and breakdown. Human chorionic gonadotropin was adm inistered as the maturation-inducing gonadotropin (GTH) and was capable of inducing maturation in a time- and dose-dependent manner. Free AA induced m aturation in a dose- and time-dependent manner and enhanced GTH-induced mat uration, while EPA, DHA, and oleic acid were ineffective. Maturation induce d by GTH was significantly suppressed by a phospholipase A(2) blocker, sugg esting that mobilization of AA was involved in GTH-induced maturation. More over, EPA and DHA exhibited a significant, dose-dependent attenuation of GT H-induced maturation. Maturation induced by GTH was inhibited in the presen ce of a cyclooxygenase inhibitor, indomethacin, and this inhibition was rev ersed by addition of AA, PGE(2), or PGF(2 alpha). PGE(2) and PGF(2 alpha) a lone were both effective stimulators of maturation, while PGE(1) and PGE(3) were ineffective. The effect of PUFAs on oocyte maturation in vitro were c orroborated with studies in vivo. Oocytes were obtained from females fed a commercial, PUFA-enriched diet (RD) and maturational behavior was compared with oocytes from females fed a natural diet (ND) with a higher EPA content and n-3:n-6 ratio. Although no significant difference was observed in the rate of spontaneous oocyte maturation, a higher percentage of GTH-induced m aturation and lower percentage of atresia were observed in RD oocytes. More over, while basal PGE production from oocytes from both groups was the same , RD oocytes produced significantly higher levels of PGF in the presence of hCG. The results from this study provide evidence for the participation of AA metabolism in GTH-induced oocyte maturation, and suggest that other PUF As and PGs may play important roles in the induction of maturation in a mar ine teleost.