Involvement of PLA2, COX and LOX in Rhinella arenarum oocyte maturation

Abstract

In Rhinella arenarum, progesterone is the physiological nuclear maturation inducer that interacts with oocyte surface and starts a cascade of events leading to germinal vesicle breakdown (GVBD). Polyunsaturated fatty acids and their metabolites produced through cyclooxygenase (COX) and lipoxygenase (LOX) pathways play an important role in reproductive processes. In amphibians, the role of arachidonic acid (AA) metabolites in P4-induced oocyte maturation has not been clarified yet. In this work we studied the participation of enzymes involved in AA metabolism ?phospholipase A2 (PLA2), COX and LOX- in Rhinella arenarum oocyte maturation. PLA2 activation induced maturation in Rhinella arenarum oocytes in a dose-dependent manner. Oocytes treated with melittin showed highest response (786% GVBD) with 0.08 µM. In follicles, PLA2 activation did not significantly induce maturation at the assayed doses (123% GVBD). PLA2 inhibition with quinacrine prevented melittin-induced GVBD in a dose-dependent manner; however, PLA2 inactivation did not affect P4-induced maturation. This suggests that PLA2 is not the only phospholipase involved in P4-induced maturation in this species. P4-induced oocyte maturation was inhibited by COX inhibitors, indomethacin and rofecoxib (653% and 633% GVBD, respectively), although it was never blocked by them. Follicles showed a similar response to these inhibitors. Participation of LOX metabolites in maturation seems to be correlated with seasonal variations in ovarian response to P4. During the February-June period (low P4 response), LOX inhibition by nordihydroguaiaretic acid (NDGA) or lysine clonixinate (LC) increased maturation up to 70%. During the July-January period (high P4 response), LOX inhibition had no effect on hormone-induced maturation.