Correlation of acrosomal status and sperm performance in the sperm penetration assay.

The sperm of some infertile men are unable to penetrate zona pellucida-free hamster oocytes but gain that ability after treatment with human follicular fluid (hFF). We asked whether altered incidences of acrosome reacted sperm explained these observations. Patient sperm failing to penetrate oocytes had fewer acrosome reactions than did healthy males, but the percentage reacted was not correlated with oocyte penetration. Sperm incubated 3 hours, then exposed to hFF, exhibited increased penetrations for 7 of 10 males, without an increase in percentage reacted sperm. Sperm incubated 22 hours before hFF treatment had penetrating ability enhanced 250- to 1000-fold, but the percentage reacted increased only sixfold. We conclude that factors other than the percentage reacted sperm are the major determinants of penetration capacity.