Serum factors stimulate the motility of human spermatozoa

Summary Motile human sperm were collected from a Percoll gradient and the effects on sperm motility of human serum, various serum fractions, follicular fluid and seminal plasma were assessed. In culture medium alone (RPMI‐1640) sperm motility was lost after about 5 h. The addition of male blood serum both enhanced sperm motility and prolonged viability very significantly. Albumin, seminal plasma and follicular fluid all stimulated sperm motility but to a much lesser extent than did blood serum. No difference was noted between male serum or female serum which had been collected during the follicular or luteal phases of hormone‐stimulated cycles and which contained high levels of oestradiol. Serum fractions obtained by separation on Sephacryl S‐300 column were tested for their ability to enhance sperm motility. The most pronounced effect, much superior to that achieved by the albumin fraction, was obtained by a fraction with a molecular weight of around 200 kD. In conclusion, certain factors in human serum, which are different from albumin, strongly support sperm motility. The high serum concentrations of oestradiol resulting from hormone stimulation for in‐vitro fertilization do not invalidate the use of serum from the same patient during sperm preparation, or in the medium used for ovum insemination and culture.