CAPACITATION OF RABBIT SPERMATOZOA IN THE UTERUS WITH SPECIAL REFERENCE TO THE REPRODUCTIVE PHASES OF THE FEMALE1

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Abstract
The capacitation of sperm (spermatozoa undergo a certain physiological change in the female tract before they are capable of fertilization) was investigated by injection of sperm into the uterus of rabbits at various reproductive phases or rabbits treated with gonadotrophin, estrogen or progesterone. Twelve hours later the injected sperm were recovered and then deposited into the top of the fallopian tubes of another rabbit that had ovulated recently. This was done to determine whether sperm so treated could fertilize the ova. Although capacitation was achieved in the uterus of immature and ovariectomized rabbits with or without the treatment of gonadotrophin or estrogen, it could not be achieved in the uterus of pseudopregnant rabbit with or without the treatment of gonadotrophin or estrogen or in the uterus of immature, ovariectomized, or estrous rabbits treated with progesterone. The inhibition of capacitation of sperm in the pseudopregnant uterus or in the uterus of rabbits treated with progesterone was not due to the poor motility of sperm, the large number of sperm, the concentration of white cells, or the possible, bacterial infection of the endometrium. However, when sperm were injected into the fallopian tubes of pseudopregnant rabbits and then recovered and deposited into the tubes of another rabbit fertilization occurred. It seems that capacitation of sperm was inhibited in the uterus under the influence of progesterone but it was not so affected in the fallopian tubes.