Acrosomal function of human spermatozoa with normal and abnormal head morphology.

In previous studies we have shown differences in the function of morphologically normal and abnormal sperm by evaluating their flagellar movements and swimming trajectories. In this study we have compared the capability of morphologically normal and abnormal human sperm to undergo an acrosome reaction after incubation with human follicular fluid. Semen samples were studied from 6 research donors and 21 semen evaluation patients. All men had normal semen by clinical criteria. Semen was prepared either by a two-step Percoll gradient centrifugation or the sperm were diluted, washed, and centrifuged three times. Sperm suspensions were incubated for 24 hours in a modified Tyrode's medium, containing 2.6% bovine serum albumin, prior to dilution with human follicular fluid. The percentage of acrosome reactions among viable sperm was assessed after 15 minutes using the supravital Hoescht stain and fluoresceinated pea lectin. Sperm head size was measured with an ocular micrometer and normal values were defined as length 3-5 microns and width 2-3 microns. At least 25 viable normal sperm, and 25 viable abnormal sperm were analyzed for acrosome reactions on each slide. With Percoll separation the percentage of acrosome reactions (mean +/- sem) for normal sperm was 38 +/- 3% vs. 22 +/- 2% for abnormal sperm (P less than 0.005). After washing, the comparable values were 12 +/- 1% vs. 5 +/- 1% (P less than 0.005). The incidence of spontaneous acrosome reactions (24 hours of incubation, no follicular fluid) was also higher for normal sperm than abnormal sperm (9 +/- 1% vs. 4 +/- 1%, P less than 0.01). These data demonstrate an association between normal sperm morphology and acrosomal function.