An investigation into the role of prostaglandins in zebrafish oocyte maturation and ovulation

This study explored the potential for ovarian-derived prostaglandins (PGs) to be involved in the regulation of oocyte maturation and ovulation in zebrafish. It was demonstrated that cultured vitellogenic follicles have the capacity to produce prostaglandin E-2 (PGE(2)) and PGF(2 alpha). in response to arachidonic acid (AA) in a concentration-dependent manner, and that AA stimulates the in vitro production of 17 beta-estradiol (E-2). The production of AA-stimulated PGF(2 alpha). Was significantly reduced by treatment with the nonselective cyclooxygenase (COX) inhibitor, indomethacin (INDO). Treatment of full-grown follicles with AA did not induce oocyte maturation as assessed by germinal vesicle breakdown, but INDO significantly decreased the rate of spontaneous maturation. Using Real-Time PCR, it was shown that follicles of different developmental size classes (primary growth and pre-vitellogenic, early-vitellogenic, and mid- to full-grown vitellogenic) express enzymes that release (cytosolic phospholipase A(2) (cPLA(2)); phospholipase C gamma 1) or metabolize (COX-1, COX-2, and prostaglandin synthase-2) AA to PG metabolites. The expression of cPLA(2) was found to be significantly greater in full-grown follicles compared to follicles of the pre- and early-vitellogenic stages. In vivo studies demonstrated that breeding groups of zebrafish exposed to 100 mu g/L INDO exhibited reduced spawning rates and clutch sizes compared with control and 1 mu g/L INDO exposed fish. In other studies, it was shown that naturally spawning groups of females exhibit increased ovarian levels of PGF(2 alpha), E-2, and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (a maturation-inducing hormone in zebrafish) near the time of ovulation compared with non-breeding females. Collectively, these experiments indicate that the AA pathway in zebrafish ovaries is involved in the regulation of oocyte maturation and ovulation and a non-selective inhibitor of COX disrupts these processes. (C) 2008 Elsevier Inc. All rights reserved.