Succinate dehydrogenase participation in porcine gamete function

Context Porcine gametes require energy for the physiological processes that allow fertilisation. Succinate dehydrogenase (SDH) plays a pivotal role in both, the tricarboxylic acid (TCA) cycle and the respiratory chain. Aims The aim of this work was to study the participation of SDH in the in vitro oocyte maturation, sperm capacitation and acrosome reaction in porcine species. Methods Cumulus–oocyte complexes (COCs) from abattoir-derived porcine ovaries were collected by aspiration and were incubated in maturation media, with the addition of increasing concentrations (0, 1, 5 and 10 mM) of malonate (a specific inhibitor of SDH). Nuclear maturation and cytoplasmatic maturation were analysed. Semen samples were incubated for 2 h in capacitating medium with 40 mM sodium bicarbonate, as sperm capacitation inducer, and the addition of increasing concentrations of malonate (0, 1, 5 and 10 mM). Sperm capacitation state and true acrosomal reaction were evaluated. SDH activity was determined in sperm and oocyte extracts by the spectrophotometric method. Key results The addition of 10 mM of malonate decreased both nuclear and cytoplasmic maturation rates (P < 0.05) without affecting COC viability (assessed using fluorescein diacetate). A lower level of capacitation (induced by bicarbonate) and acrosome reaction (induced by follicular fluid) was observed with the addition of 5 mM of malonate (P < 0.05) without affecting motility and viability of sperm at this concentration. The activity of SDH was 0.35 ± 0.1 × 10−5 and 2.37 ± 0.9 × 10−5 U/COC for immature and in vitro matured COC extracts (P < 0.05) respectively, and 0.44 ± 0.16 U/1010 sperm for boar sperm extracts. Conclusions In conclusion, because it has been proposed that aerobic and anaerobic metabolic pathways of cells are changed depending on the oxygen availability and the composition of metabolic substrates in their environment, our results suggest that energy obtained through the mitochondrial respiration (TCA cycle and oxidative phosphorylation) is necessary to support oocyte maturation, sperm capacitation and acrosome reaction in the porcine species. Implications The study of enzymatic activity in gametes is essential for understanding the mechanisms that control the energy production required to achieve successful fertilisation. This knowledge has significant implications for the development of assisted reproductive technologies.