Factors affecting human sperm penetration of zona-free hamster ova

The effects of in vivo and in vitro aging of hamster ova, protein supplementation of culture media, sperm concentration, and sperm motility on penetration of zona-free hamster ova by human sperm were investigated. Penetrability of ova was significantly lowered by 2 to 4 additional hours of in vivo aging or by an additional 3 hours of in vitro aging. A comparison was made of the effects of the addition to the media of human preovulatory serum and human serum albumin, and the penetrating ability of human sperm was increased with the addition of 10% human preovulatory serum. Sperm motility was also better maintained in the presence of 10% serum. Maximum penetration occurred after 3 hours of sperm-egg interaction following a 3-hour preincubation period with a sperm concentration of 5 x 10(6) motile sperm per milliliter. When motile sperm concentration was maintained at 1 X 10(7) motile sperm per milliliter, there was no correlation between penetrating ability and percentage of motility. These factors should be controlled to allow reproducible results with the hamster test.