Effects of nicotine on sperm attachment and penetration of zona-free hamster eggs.

A previous study from this laboratory showed that nicotine in vitro has deleterious effects on sperm motion characteristics. This study was conducted to evaluate the effects of nicotine on the ability of human spermatozoa to attach and penetrate zona-free hamster eggs. Spermatozoa from fertile donors, washed free of seminal plasma, were incubated with medium (control) and 0.1, 1, 5, and 10 mM concentrations of nicotine (concentrations estimated to approximate residual concentrations of nicotine in the testes of heavy smokers) for 18 h at 37 degrees C in a humid 5% carbon dioxide incubator. The sperm preparations were then mixed with enzymatically denuded hamster eggs and incubated for 3 h at 37 degrees C. The oocytes were examined by phase-contrast microscopy to enumerate the rates of sperm attachment and penetration. The data were analyzed by a paired t test and repeated measures analysis of variance using the arcsine transformation of the percentages. The percentages of eggs with attached spermatozoa significantly declined in a dose-dependent manner, the highest inhibition being at 10 mM (F = 24). The rate of sperm penetration was even more significantly decreased with the increase in nicotine concentrations in the following order: 10 mM (F = 56) > 5 mM (F = 30) > 1 mM (F = 44) > 0.1 mM (F = 12). Nicotine concentrations of 0.1 mM and above negatively affected sperm penetration of zona-free hamster eggs.