Effects of progesterone on in vitro sperm capacitation and egg penetration in the golden hamster.

Progesterone (P) is postulated to have a physiological role in vivo during sperm capacitation and/or during sperm-egg interaction as a cofactor for induction of the acrosome reaction. Effects on in vitro fertilization were tested by adding P (0.01-2 micrograms/ml) to sperm during capacitation (4-6 h) or after capacitation during sperm-egg interaction for 1 h. Additionally, to test for acceleration of the onset of capacitation by P, eggs were inseminated with sperm that were incubated with P for 3.5 and 5 h. Neither the solvent dimethyl sulfoxide nor P affected the motility or vigor of treated sperm. The effects of P on egg penetration were dependent on the dose, the temporal sequence of its addition to sperm (i.e., before or after capacitation), and the duration of sperm exposure. Capacitation of sperm with 20 ng/ml P for 5 h, but not 3.5 h, increased the percentage of eggs penetrated by sperm over controls (52.65 +/- 4.01% vs. 39.30 +/- 5.18%, p < 0.05). But P (0.01-2 micrograms/ml), either added after capacitation (4.5 h) during sperm-egg coincubation (1 h) only, or present (1 micrograms/ml) throughout capacitation (4-6 h) and sperm-egg coincubation (1 h), did not increase egg penetration over control levels. In conclusion, the best results occurred with a protocol that mimicked in vivo conditions of capacitation time (5 h) and preovulatory oviductal levels of P (20 ng/ml).