Phospholipase A2 activity in fresh and cryopreserved spermatozoa from boars

Abstract

The enzyme phospholipase A2 (PLA2) is considered to play an important role in the fertilizing ability of mammalian spermatozoa, but PLA2 activity has not been identified in boar spermatozoa. Fertility rates obtained using cryopreserved boar semen are considerably less than those with fresh boar semen, which might be attributed to altered PLA2 activity. Phospholipase A2 activity, determined by the formation of radiolabelled fatty acid from a radiolabeled phospholipid substrate, was successfully detected in the sonicates and acid extracts of boar spermatozoa. The PLA2 in acid extracts was calcium-dependent, active at neutral and alkaline pH and was maximized with increasing incubation temperatures, time and spermatozoal protein. Assaying acid extracts under conditions of 35 °C, 24 h, pH of 7.5 and 2 mM calcium, the PLA2 activity of freshly collected boar spermatozoa was found to be 8.22 ± 1.47 pmoles palmitic acid h−1 mg−1 protein (mean ± SE). Matched samples of spermatozoa exposed to cryopreservation had a significantly lower (P < 0.05) activity of 4.26 ± 0.59 pmoles palmitic acid h−1 mg−1 protein. This study has identified PLA2 in boar spermatozoa for the first time and determined that its activity is reduced by procedures known to reduce fertility. Key words: Phospholipase, boar, semen, cryopreservation