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W. RICHARD DUKELOW and WILLIAM L. WILLIAMS

Spermatozoa attain the ability to fertilize an ovum by incubation in the reproductive tract for a given period of time (capacitation). Recently Bedford & Shalkovsky (1967) and Bedford (1967) have indicated that the final stages of capacitation may be species-specific, normally occur in the oviduct and require from 0·5 to 2·5 hr in the rabbit. Capacitation enables the spermatozoon to penetrate the cumulus oophorus, corona radiata and to initiate fertilization. The work of Dukelow, Chernoff & Williams (1967) suggested that the final stages of capacitation may involve an ovum-sperm interaction occurring on the surface of, or within, the zona pellucida. These workers have suggested that the oviducal environment was detrimental to the fertility of uterine capacitated spermatozoa resident in the oviduct for several hours before ovulation. The objectives of the present study were to determine (1)

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WILLIAM L. WILLIAMS and CHARLES E. HAMNER

Summary.

Rabbit, human and cock spermatozoa collected and washed without exposure to light respired very slowly or not at all. Brief exposure to white light of less than a minute's duration stimulated normal rates of respiration. Ubiquinone (UQ, Co-enzyme Q), seminal plasma, in-utero incubation, and dinitrophenol each markedly stimulated the respiration of spermatozoa protected from light. Ubiquinone10 was effective with cock spermatozoa while UQ1 was superior to UQ3 or UQ4 with rabbit spermatozoa. Ubiquinone1 appeared more effective than UQ3 for human spermatozoa.

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C. E. HAMNER and WILLIAM L. WILLIAMS

Summary.

A fourfold increase in oxygen uptake by rabbit spermatozoa incubated in the rabbit uterus and a twofold increase in cock spermatozoa incubated in the hen's oviduct over ejaculated spermatozoa is the first reproducible biochemical change to be demonstrated in spermatozoa residing in the female genital tract. It was shown that these rapidly respiring spermatozoa were capacitated because they fertilized 18% of the eggs tested as compared to no eggs fertilized by freshly ejaculated spermatozoa.

It was found that oviduct fluid in vitro stimulates respiration fivefold in spermatozoa protected from light. Increase in oxygen consumption by spermatozoa residing in the female reproductive tract may be an important part of the capacitation process.