Effect of Progesterone and Oestradiol on Sperm-zona Binding and Acrosome Reaction in Bovine Spermatozoa after Thawing

This study was conducted assess spermatozoa binding capacity to the oocyte in the presence of 0.1 or 0.5 μg/ml progesterone (P4) or a combination of 0.5 μg/ml P4 with 0.1 μg/ml oestradiol (OE). The number of oocyte-bound spermatozoa in the presence of progesterone was significantly higher (p < 0.05 to p < 0.001) when compared with the control samples, that were incubated in the absence of P4. Spermatozoa binding to the zona pellucida (ZP) of the oocyte were concentration-dependent - significantly higher numbers of spermatozoa were bound in the presence of 0.5 μg/ml P4, when compared with that of 0.1 μg/ml P4. Oestradiol at 0.1 μg/ml concentration used impaired the effect of progesterone-mediated sperm-oocyte binding. The incidences of acrosome-reacted (AR) spermatozoa bound to the ZP - following 0, 60, 120 and 180 min. incubation in the presence and absence of 1 μg/ml progesterone was also assessed. Only at 180 min of incubation a higher (p < 0.001) incidence of the AR-spermatozoa was found in sperm-ZP complexes incubated in the presence or absence of progesterone, being 56.5 ± 11.1 and 43.2 ± 8.8 % respectively. In conclusion, progesterone enhances the sperm-ZP binding capacity. Progesterone affects the incidences of AR on zona-bound spermatozoa only after prolonged co-culture.