Effects of taurine and hypotaurine supplementation and ionophore concentrations on post-thaw acrosome reaction of dog spermatozoa

Abstract The aim of this work was to study of the effect of the amino acids (AA) taurine (T) and hypotaurine (H) and of different calcium ionophore concentrations on the ability of capacitated frozen-thawed dog sperm to undergo the acrosome reaction (AR). Fifteen ejaculates grouped into five pools were used. Sperm was frozen at a concentration of 80 × 10 6  sperm cells/mL in the Uppsala Equex extender (UE) supplemented with 25, 50 and 75 mM of either AA. The UE extender without T or H was used as control. After thawing, sperm was capacitated with Canine Capacitation Medium for 20 min. Sperm was then challenged with calcium ionophore A23178 at 0, 2.5 and 10 μM concentration and evaluated for integrity of plasma and acrosome membranes after 5, 15 and 30 min of incubation, utilizing PI/Fitc-PNA fluorescent staining and flow cytometry. Sperm cryopreserved in UE supplemented with 50 mM T (UE 50T) had higher AR rates than sperm cryopreserved with UE 75T, UE 25H and UE 50H, but AR rates were similar to semen frozen with the control extender. Challenges with 2.5 and 10 μM/L of calcium ionophore increased AR in frozen-thawed sperm incubated for 5, 15 and 30 min. The combination of calcium ionophore concentration and incubation time resulting in the highest AR rate was 10 μM and 15 min.