Penetration of Zona-Free Hamster Eggs by Liposome-Treated Sperm from the Bull, Ram, Stallion, and Boar1

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Abstract
Spermatozoa from each of four rams, four stallions, and three boars (six semen samples) were treated with dilauroylphosphatidylcholine (PC12) liposomes and compared with control bull sperm to induce the acrosome reaction (AR) and study possible penetration of the sperm into zona-free hamster eggs. Diluted sperm were incubated with several concentrations of PC12 for 7 min at 39.degree. C prior to insemination of the hamster eggs in vitro. The sperm from the bull were diluted to 106 cells/ml as previously studied. Sperm from the ram, stallion, and boar were diluted to 6 .times. 106 and 20 .times. 106 celkls/ml. After addition to the eggs, the sperm concentration was reduced by 75 percent. Inseminated eggs were incubated with sperm for 3 h at 39.degree. C prior to being fixed, stained, and observed for sperm penetration. At an initial concentration of 6 .times. 106 cells/ml, bull sperm treated with 36.7 .mu.M PC12 achieved an egg penetration rate of 92%, whereas under nearly identical conditions stallion spermatozoa achieved only 54% egg penetration. Under similar conditions, ram spermatozoa failed to penetrate eggs, but when the initial sperm concentration was increased to 20 .times. 106 cells/ml, sperm incubated with 51.5 .mu.M PC12 achieved 52% egg penetration. Boar spermatozoa treated with PC12 at either sperm concentration failed to exhibit an AR or penetrate hamster eggs. In general, as PC12 concentration increased the percentage of sperm with an AR increased and sperm motility decreased. It is concluded that 1) PC12 lipsosomes are effective in inducing the AR in sperm from the bull, ram, and stallion, but under conditions tested are ineffective with boar sperm; 2) these acrosome-reacted spermatozoa will penetrate zona-free hamster eggs and so may provide insight into the fertilizing ability of sperm from individual males of several species.