Effects of Prolonged Sperm Preincubation and Elevated Calcium Concentration on Fertilization of Cumulus-Free Mouse Eggs in Vitro.

Freshly superovulated eggs of Jcl: ICR mature mice that had been freed from their cumulus oophorus with hyaluronidase were fertilized by epididymal spermatozoa preincubated for various periods in a modified Krebs-Ringer bicarbonate medium (TYH). Calcium concentration in the fertilization medium was elevated to the twice (3.42 mM) or to the 3 times (5.13 mM) of TYH (1.71 mM) and all incubations were performed at 37C under 5% CO2 in air. Both the sperm preincubation time and the concentration of calcium in the fertilization medium were found to exert significant effects on fertilization of cumulus-free eggs in vitro, and the highest fertilization rate was obtained when the cumulus-free eggs were inseminated with 150 min-preincubated spermatozoa in a medium with 3.42 mM calcium.