Fertilization of Rat Eggs in Vitro

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Abstract
Rat eggs were recovered from oviducts and inseminated with sperm collected from either the uterus of mated females or the cauda epididymis of males. A mixture of a modified Krebs-Ringer bicarbonate solution and rat serum (4:1) was usually used to incubate the sperm and eggs for 8–12 h. The presence of bovine serum albumin and rat serum in the medium appeared to be very important for the fertilization of rat eggs in vitro. When eggs recovered 1–5 h after ovulation were inseminated with sperm recovered from the uterus of females mated 0.5–1, 4–5, and 10–11 h previously, the proportions of eggs penetrated were 4–7, 85–95, and 32–55%, respectively. Eggs obtained from superovulated mature and immature females were as fertilizable in vitro as were those recovered from the naturally ovulated females. Sperm penetration, however, was not observed when preincubated epididymal sperm were used under the present experimental conditions. This fact and the significantly higher proportions of eggs penetrated by sperm recovered from the uterus at 4–5 and 10–11 h than at 0.5.–1 h after mating demonstrated that rat sperm do need capacitation in the female tract before they are capable of penetrating the egg. The time required for capacitation of rat sperm in the female tract appeared to be about 4–5 h. Polyspermy and the presence of supplementary sperm in both the fertilized and unfertilized eggs were very frequently observed.

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