The effect of relaxin on the motility of sperm in freshly thawed human semen.

In an attempt to improve the motility of thawed spermatozoa after 1 week of its being frozen, we treated ten normal semen samples with 16.7 nmol relaxin and 6 mmol caffeine. Motility and grade of forward progression were examined after thawing. Caffeine significantly improved motility of spermatozoa. Relaxin, when added to semen at the time of thawing, improved motility and grade of forward progression significantly. This effect was not seen if relaxin was added before freezing. These results suggest that the biologic activity of relaxin is adversely affected by freezing and thawing in seminal plasma. These observations may have clinical importance for the improvement of motility of frozen spermatozoan samples at the time of artificial insemination and for the possible improvement of pregnancy rates.