Effect of heparin on capacitation/acrosome reaction of equine sperm

The onset of sperm capacitation/acrosome reaction was evaluated using heparin. Equine semen was incubated at 38 degrees C for 4.5 h in culture medium with and without 10 micrograms/mL heparin and with and without 0.1 microM of Ca2+ ionophore. Sperm acrosome reaction was detected using chlortetracycline fluorescence (CTC) and transmission electron microscopy (TEM). The CTC assay provided staining patterns that corresponded with the capacitation/acrosome reaction in other mammalian species (man, mouse, guinea pig). The percentages of incapacitated sperm (PUC), capacitated acrosome-intact sperm (PC), and acrosome-reacted sperm (PAR) were evaluated following incubation times of 0.5 and 4.5 h in heparin-free and heparinized medium, and at 4.5 h only in sperm exposed to Ca2+ ionophore. The CTC assay was highly correlated with TEM for estimation of PAR. At 4.5 h, heparinized medium reduced PUC and increased PC and PAR, in comparison with heparin-free medium. Addition of Ca2+ ionophore to the medium reduced PUC and increased PC and PAR at 4.5 h, as compared with sperm in ionophore-free medium. Incubation time also affected PUC, PC, and PAR in heparin-free and heparinized medium without ionophore. The PUC was greater at 0.5 h than at 4.5 h, and PC and PAR were less at 0.5 h than at 4.5 h. It would appear that the initiation of capacitation/acrosome reaction of equine sperm in vitro is accelerated by heparin.