Heparin‐induced capacitation: a comparison between the bull and stallion

Summary Spermatozoa were incubated with 0, 10, 50 or 100 μg heparin/ml for 4 h at 37°C (bull) or 39°C (stallion) in 5% CO 2 . Spermatozoa were then challenged with 10 μM‐calcium ionophore A23187 at 0, 2 and 4 h of incubation for an additional 30 min. Samples were evaluated for the % of motile and acrosome‐reacted spermatozoa. The spermatozoa of both species exhibited a decline in the % of motile spermatozoa during incubation over 4 h, and this decline was similar for heparin and non‐heparin‐treated stallion spermatozoa (P>0.05). Within incubation times the % of acrosome‐reacted stallion spermatozoa during incubation was similar (P<0.05) among heparin and non‐heparin‐treated spermatozoa. As for bull spermatozoa, addition of 10 μM‐A23187 to stallion spermatozoa induced more acrosome‐reactions in heparin‐treated than in non‐heparin‐treated spermatozoa (P<0.05). However, maximal inductions of acrosome reactions following ionophore challenge occurred in stallion spermatozoa after 4 h incubation with ≥50 μg heparin/ml. Bull and stallion spermatozoa incubated with heparin exhibited higher (P<0.05) % of acrosome‐reacted spermatozoa after challenge with A23187 than did non‐heparin‐incubated spermatozoa, suggesting that they may have undergone capacitation during incubation with heparin. Although incubation with 10 μg heparin/ml was sufficient to induce capacitation in bull spermatozoa, stallion spermatozoa required incubation with ≥50 μg heparin/ml.