Species-Specificity of Sperm Capacitation in the Rabbit

The most important aspect of the relationship between mammalian spermatozoa and the female tract to be revealed so far is the process of capacitation, which finally confers upon spermatozoa their ability to fertilize (Austin, 1951 ; Chang, 1951). The changes which take place in spermatozoa in the female tract, as a concomitant of capacitation, remain uncertain. One approach to this problem lies in identification of the environmental factors necessary for capacitation. It has been claimed that rabbit spermatozoa may be capacitated in the bladder, colon and anterior chamber of the eye (Noyes, Walton & Adams, 1958), and by incubation in vitro with uterine fluids or with β-amylase (Kirton & Hafs, 1965). In these investigations, however, fertilizing ability was assessed by sperm deposition into the oviducts soon after ovulation. This must leave doubt as to whether capacitation was completed outside the female tract. As nothing is known of the species-specificity requirement for complete functional capacitation, in the present study attempts have been made to capacitate rabbit spermatozoa in the cat, ferret, guinea-pig and the rat. Approximately 4 to 8 million epididymal rabbit spermatozoa in 0·03 ml Hanks' solution were inseminated in oestrous cats, ferrets, guinea-pigs and rats into each uterine horn, which was then ligated close to the cervix. Rabbit spermatozoa survived for not more than 12 hr in the cat, ferret and guinea-pig, and