Pentoxifylline acts synergistically with A23187 to increase the penetration of zona‐free hamster oocytes by cryopreserved human spermatozoa

The number of cryopreserved human spermatozoa which penetrated zona‐free hamster oocytes afier stimulation with 2μmol A23187 per litre was increased by the hrther addition of 0.6 or 3.6 mmol pentoxifjrlline per litre. With spermatozoa prepared by washing by repeated centrifugation, the median numbers of sperm headd/egg were 1.9, 7.9 and 10.8 in the presence of 0, 0.6 or 3.6 mmol pentoxifylline per litre, respectively. A similar effect was observed with spermatozoa prepared on a Percoll gradient. As A23187 inhibited sperm motility, and this was exacerbated by pentoxifylline, the increased penetration rate of hamster oocytes cannot be explained by improved sperm motility. The number of spermatozoa stimulated to acrosome react by 2 μmol A23187 per litre was increased 3‐fold by 3.6 mmol pentoxifylline per litre and 4‐fold by 5 mmol caffeine per litre. These data suggest that CAMP may act synergistically with Ca²⁺ to stimulate the acrosome reaction. Pentoxifjrlline may improve the fertility of poor‐quality human spermatozoa by enhancing their ability to respond to the Ca²⁺ signal produced by binding to the zona pellucida.