Pentoxifylline improves sperm binding to the zona pellucida in the hemizona assay

Objective: To evaluate the effect of pentoxifylline on sperm binding capacity to zona pellucida (ZP) using the hemizona assay (HZA). Design: The fertility potential of 82 men was evaluated by routine semen analysis. Each ejaculate was incubated with or without pentoxifylline (3 mM) in Ham's F-10 medium (Flow Laboratories, Irvine, Scotland) before the HZA. The effect of the pentoxifylline treatment on sperm-binding capacity to ZP was assessed by the hemizona index. Results: The mean hemizona indexes with medium or pentoxifylline treatment were 23% ± 2.1% (mean ± SE) and 41% ± 3.4%, respectively. Taking into consideration a significant change of the hemizona index on rising above the intra-assay coefficient of variation (±8%) after pentoxifylline treatment, 73.1% of specimens improved, 19.5% deteriorated, and 7.4% remained unchanged. Using a threshold hemizona index of 23% as a discriminator between fertile and infertile specimens, 43.5% of the 'pentoxifylline-improved' samples ascended to the fertile zone (>23%). No correlations were found between sperm variables in the raw semen and the effect of pentoxifylline on sperm binding capacity. Conclusion: Pentoxifylline may improve the binding capacity of human spermatozoa. However, this effect is confined to a selected group of patients and cannot be predicted by the basic sperm variables. Thus, to avoid uncertain or damaging effects of pentoxifylline while preparing sperm suspension for assisted reproductive techniques, it is recommended that its effect be tested by the HZA system before its use.