Differential activities of malate and isocitrate NAD(P)-dependent dehydrogenases are involved in the induction of capacitation and acrosome reaction in cryopreserved bovine spermatozoa.

Sperm catabolic processes produce energy for capacitation and acrosome reaction induction required for oocyte fertilization. The aim was to determine metabolic enzymes' activities and their participation in the supply of energy and generation of the redox state to acquire fertilizing capacity. Capacitation was induced with heparin and quercetin, and the acrosome reaction with progesterone. Enzymatic activities were determined spectrophotometrically. The chlortetracycline and differential-interferential contrast microscopy/tryptan blue techniques were used to evaluate capacitation and acrosome reaction, acrosomal integrity and sperm viability respectively. A 2 : 1 and 3 : 1 ratio were obtained for isocitrate dehydrogenase (IDH)-NADP/NAD and malate dehydrogenase (MDH)-NADP/NAD activities respectively. MDH-NADP activity remained constant with different treatments, unlike MDH-NAD activity, which diminished with both capacitation inducers and in acrosome-reacted spermatozoa previously treated with heparin (P < 0.05). IDH-NADP decreased its activity 50% in spermatozoa capacitated with heparin and acrosome reacted with progesterone (P < 0.05). Capacitation and acrosome reaction processes induced with heparin and progesterone, respectively, involve a differential oxidative metabolism, with the participation of MDH-NAD(P) and IDH-NAD(P) enzymes, whose activities would be linked to the malate-aspartate, lactate-pyruvate and isocitrate cytosolic-mitochondrial shuttles. These enzymes play a major role in supplying reduction equivalents and/or energy required for capacitation and acrosome reaction in cryopreserved bovine spermatozoa.