Biology of Reproduction, Vol 9, 404-414, Copyright © 1973 by Society for the Study of Reproduction

Immunological Assessment of Surface Changes of Rabbit Sperm Undergoing Capacitation

¹ Division of Reproductive Biology, Department of Obstetrics and Gynecology, School of Medicine and Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19174

Sperm capacitation may involve the removal of seminal plasma factor(s) from the surface of the sperm. To determine the presence of seminal plasma components and in order to follow their release or alteration, antibodies to rabbit seminal plasma were produced in guinea pigs. The agglutinating ability of rabbit spermatozoa when mixed with antiserum was followed after washing the sperm cells for extensive periods. Eighteen hours of washing did not diminish the agglutination reaction. However, when ejaculated spermatozoa were incubated in utero, the agglutination of the sperm cells induced by the antiserum to seminal plasma diminished with time in utero. Additional data indicated that a higher percentage of cleaved ova resulted following insemination in vitro with uterine spermatozoa recovered at increasing intervals after coitus (9, 44, 55, and 74% at 3, 6, 12, and 18 h, respectively). Furthermore, utilizing the binding of ¹⁴C-labeled antibodies against rabbit seminal plasma, the sperm-bound seminal plasma components were shown to be bound tightly to the sperm and were not removed during 24 h of incubation in vitro in a defined medium. However, when washed ejaculated sperm are incubated in uterine fluid, the uptake of ¹⁴C-antibodies falls off with increasing time of incubation, up to 65% decrease with 6 h of incubation. These findings may provide a basis for a rapid quantitative assay for sperm capacitation.