Factors Regulating Changes of Head-to-Head Agglutinability in Boar Spermatozoa During Epididymal Transit and Capacitation In Vitro - Review-

In boar spermatozoa, the head-to-head agglutinability changes in parallel with the development of the fertilizing ability. Namely, both abilities gradually increase in the distal caput and corpus epididymides, but are subsequently suppressed in the cauda epididymidis. It has been postulated that these changes of the agglutinability are controlled via sperm interaction with specific epididymal plasma factors including agglutination mediators (agglutinins) and inhibitors (anti-agglutinins). Expression of these abilities (sperm agglutination and capacitation) is hardly observed in spermatozoa immediately. after ejaculation, but it occurs during incubation in a capacitation medium. Recently, we have purified and characterized epididymal plasma anti-agglutinin for boar spermatozoa. Moreover, we have conducted a series of experiments to reveal biological significance and mechanism of the head-to-head agglutination and have accumulated data indicating that boar sperm agglutination is mediated by capacitation-supporting factors including calcium, bicarbonate and sterol acceptors. This review introduces our recent data and discusses a possible mechanism for suppression of the agglutinability in the distal epididymidis and relationship between agglutinability and fertilizing ability.