Heparin and quercitin generate differential metabolic pathways that involve aminotransferases and LDH-X dehydrogenase in cryopreserved bovine spermatozoa

Heparin and quercetin induce capacitation in spermatozoa through membrane receptor binding and inhibition of Ca-ATPase of the plasma membrane, respectively. Although capacitation is energy intensive, ammonia from amino acid metabolism can inhibit respiration and Krebs cycle activity. The objective was to determine activities of key enzymes in bull spermatozoa that contribute to the redox state and supply energy for capacitation. Malate dehydrogenase (MDH-NAD+), alanine and aspartate aminotransferases (ALT, AST), and lactate dehydrogenase-X (LDH-X) were measured spectrophotometrically (340 nm); mean (±S.D.) activities in control spermatozoa were 7.65 ± 1.67, 0.45 ± 0.05 and 0.74 ± 0.14 × 10−2 U/108 spermatozoa for MDH-NAD+, ALT and AST, respectively, and were 2.83 ± 0.66 U/108 spermatozoa for LDH-X. Heparin decreased (P < 0.05) activities of MDH-NAD+, ALT, AST and LDH-X (78, 53, 66 and 66% of control levels, respectively); we inferred that amino acid catabolism was decreased. Quercetin decreased (P < 0.05) activities of MDH-NAD+ and ALT (60 and 49% of control levels), but activities of AST and LDH-X were not significantly different from controls; apparently maintenance of LDH-X activity supplied pyruvate for cellular metabolism. The proportion of capacitated spermatozoa in controls (8.5 ± 1.73%) was substantially increased (P < 0.05) by treatment with either heparin (36.2 ± 4.5%) or quercetin (32.8 ± 4.7%), there was no significant difference among groups for acrosomal integrity and sperm viability. In conclusion, heparin- or quercetin-induced capacitation affected different metabolic pathways that modulated the redox state and oxidative metabolism in cryopreserved bovine spermatozoa.