Inhibition of sperm motility by bovine serum components

Various sources and components of mammalian sera were evaluated for their ability to maintain or inhibit sperm motility. Human, rabbit, hamster, and porcine sera were equal in ability to maintain motility of human sperm. Four sources of fetal calf serum and one source of neonatal calf serum were unable to maintain motility of human sperm or sperm-fertilizing potential. In the presence of human serum, fetal calf serum actually inhibited human sperm motility. Fetuin, a component of fetal calf serum, contained the inhibitory activity. An inhibitory effect of fetuin on porcine and caprine sperm motility was also observed. The inhibitory activity resided in the second peak when fetuin was separated by isoelectric focusing. The sperm head membranes remained impermeable to dye, and mitochondrial membrane potential was maintained after motility had been reduced to almost zero by incubation with fetuin and fetuin fractions. Fetuin or the active portion of the molecule may be a useful component of a vaginal contraceptive and in research where inhibition of motility is desirable.