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Inhibition of Mammalian Fertilization in Vitro by Membrane Vesicles from Seminal Plasma

Summary Vesicle fractions I and II, isolated from rabbit seminal plasma following ultracentrifugation, inhibited fertilization of rat eggs in vitro. Fertilization was reduced by 65% when the medium contained 17 μg protein/ml Fr I and by 57% when it had 5 μg protein/ml Fr. II. It was completely prevented with 83-155 and 43-85 μg protein/ml Fr I and II, respectively. Addition of 266-525 μg protein/ml whole seminal plasma or 38-175 μg protein/ml nonsedimenting seminal plasma components (Fr III) caused dissolution of the zona pellucida by constituents that were heat labile. Fertilization was inhibited by seminal plasma and promoted by Fr III. Electron micrographs of spermatozoa following incubation indicated that vesicle containing fractions from rabbit seminal plasma prevent breakdown of the plasma membrane covering the acrosome region of the head. The results are interpreted as suggesting that both classes of seminal plasma vesicles block fertilization by inhibiting sperm capacitation under defined in vitro conditions. This work was supported by N.I.H. Contract No. 1-HD-3-2781. We are grateful to Mrs. Rose Bartke and Mr. John Whitney for their skillful assistance. The electron micrographs were kindly prepared by Dr. N. Barwell, Beth Israel Hospital, Boston.