The effects of melatonin on sperm motility in vitro in Wistar rats.

The effects of physiological concentrations of melatonin on motility of spermatozoa from Wistar rats were assessed in vitro. Melatonin had dose-dependent negative effects on sperm forward progression, the quality of sperm motility and on a sperm motility index. Some, but not all of these effects were due to ethanol (0.5% final concentration) which was used as a solvent for melatonin. Addition of ethanol to the incubation medium altered the pH, and increased pH had a significant negative effect on all aspects of sperm motility. Finally, the overlay of oil, which is a routine part of many sperm culture systems, had an ameliorating effect that was probably because of the lipophilic nature of melatonin.