Macromolecular inhibitor of fertilization in rabbit seminal plasma

A large (86S) glycoprotein isolated from rabbit seminal plasma acts on sperm cells to block fertilization. The proportion of fertilized eggs recovered from does 1 day after tubal insemination of sperm 5-6 hr before or 2-3 hr after ovulation was significantly depressed when uterine-capacitated spermatozoa were exposed to this substance at concentrations of 20-72 mug of protein/ml. Rabbit seminal plasma was estimated to have about 2 mg/ml of this factor. Another large glycoprotein ( approximately 138S) is also present in rabbit seminal plasma; the function of this molecule awaits elucidation.