Effect of Test-yolk upon human sperm acrosome reaction

Human spermatozoa stored in Test-yolk buffer show an increased rate of fusion with zona-free hamster oocytes as compared with freshly ejaculated spermatozoa. Therefore, in this work, we studied the kinetics of the acrosome reaction and fertilization using fresh and TEST-yolk stored human spermatozoa in order to determine whether the rate fertilization was related to the rate of acrosome reaction. The semen samples were divided in two aliquots, one was used fresh (control) and the other stored for 48 hours at 4 degrees C in TEST-yolk buffer (experimental). Spermatozoa of each aliquot were evaluated every two hours for: a) the incidence of acrosome reaction, as studied by scanning electron microscopy, and b) their ability to fuse with zona-free hamster oocytes. The results showed that--as a function of the incubation time--there was an increase in the percentage of acrosome reaction, both in controls (zero to 28.3%) and in the experimental ones (5 to 27.8). It was also found that there were no significant differences between the incidence of the acrosome reaction when using fresh or TEST-yolk treated spermatozoa. On the other hand the rate of fertilization was significantly (p < 0.05) higher when TEST-yolk stored (experimental) spermatozoa were used as compared with the use of fresh (control) spermatozoa. These results suggest that the increase in the rate of fertilization when using TEST-yolk stored spermatozoa is not associated with an increase in the rate of the acrosome reaction, but most probably to an improvement in the efficiency of the gamete membrane fusion.