The use of strontium-substituted media for capacitating human spermatozoa: an improved sperm preparation method for the zona-free hamster egg penetration test

An improved procedure for human sperm capacitation based upon calcium deprivation using a modified Tyrode’s medium is described. Replacement of CaCl2 by SrCl2 significantly increased the penetration of zona-free hamster eggs after 20hours of sperm preincubation, compared with parallel sperm aliquots incubated in normal medium. The effect of an extra 4hours’ sperm preincubation produced no significant shift in fertilizing ability. Additon of 0.1mM ethyleneglycol-bis-(β-amino-ethylether)-N,N,N′ ,N′ -tetraacetic acid (EGTA) to the strontium-substituted medium resulted in a further significant increase in the penetration rate as well as a significant increase in polyspermy. The average increase in the penetration capacity (penetration rate × polyspermy) of the strontium/EGTA-preincubated spermatozoa was approximately tenfold, with no significant shift as a result of an extra 4 hours’ preincubation.