In vivo fertilization after initiation of sperm motility in the hamster epididymis.

Hamster spermatozoa, collected from the caput and the cauda of the epididymis, are known to differ in their motility. They do not normally acquire fertilizing ability until they reach the proximal portion of the cauda epididymidis. The aim of the present investigation was to test the fertilizing capacity of spermatozoa from the caput epididymis after initiation. Sperm cells were incubated by adding 10 mM caffeine and 20-30 p. 100 epididymal plasma to the culture medium. Superovulated females were inseminated in utero and the eggs recovered 14 h after ovulation. In these conditions, 22 p. 100 of the ova were fertilized. The possibility that the increased motility of the caput epididymal spermatozoa might reflect an increase in fertilizing ability is discussed.