In vitro fertilizaton and the sperm acrosome reaction in the hamster

Abstract The feasibility of procuring fertilization of ovulated hamster eggs in vitro with epididymal spermatozoa has been confirmed, and additional evidence is brought forward to show that a period of just under four hours is needed for sperm capacitation in vitro . It has also been found that follicular eggs can be fertilized in vitro with epididymal spermatozoa, and at a higher incidence than ovulated eggs. Female tract secretion in the hamster therefore play no unique role in sperm capacitation or sperm penetration into eggs. A close correlation, both in time and the nature of effective media, existed between the acquisition of fertilizing capacity by spermatozoa and the occurrence of the sperm acrosome reaction. The highest incidence of spermatozoa showing the acrosome reaction was seen when the cells were incubated in the contents of mature follicles; the incidence was lower with the contents of part‐grown follicles and with the secretions of the Fallopian tube. Neither the egg nor its investments appear to be the source of significant amounts of the agent or agents responsible. Induction of the acrosome reaction by follicular contents showed partial species specificity. No reactions were seen with homologous aqueous humor and fluid hen egg‐white. From observations on the frequency of polyspermy and numbers of supplementary spermatozoa it is inferred that the efficiency of both the zona reaction and the block to polyspermy increases during preovulatory follicular enlargement to reach a peak during the first 2 or 3 hours after ovulation.