Main content area

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

Ortiz, Maria Eugenia, Bühler, Marta Inés, Zelarayán, Liliana Isabel
Zygote 2014 v.22 no.4 pp. 440-445
Rhinella arenarum, amphibians, arachidonic acid, dose response, germinal vesicle, indomethacin, lipoxygenase, lysine, melittin, metabolism, metabolites, nordihydroguaiaretic acid, phospholipase A2, phospholipases, progesterone, prostaglandin synthase, quinacrine, seasonal variation
In Rhinella arenarum, progesterone is the physiological nuclear maturation inducer that interacts with the oocyte surface and starts a cascade of events that leads 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, to date, the role of arachidonic acid (AA) metabolites in progesterone (P₄)-induced oocyte maturation has not been clarified. In this work we studied the participation of three 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 when treated with 0.08 μM melittin showed the highest response (78 ± 6% GVBD). 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 finding suggests that PLA₂ is not the only phospholipase involved in P₄-induced maturation in this species. P₄-induced oocyte maturation was inhibited by the COX inhibitors indomethacin and rofecoxib (65 ± 3% and 63 ± 3% GVBD, respectively), although COX activity was never blocked by their addition. Follicles showed a similar response following the addition of these inhibitors. Participation of LOX metabolites in maturation seems to be correlated with seasonal variation in ovarian response to P₄. During the February to June period (low P₄ response), LOX inhibition by nordihydroguaiaretic acid or lysine clonixinate increased maturation by up to 70%. In contrast, during the July to January period (high P₄ response), LOX inhibition had no effect on hormone-induced maturation.