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Abstract
The acrosomal status of human spermatozoa was studied in relation to the score of the sperm penetration assay (SPA) at low-temperature (4 d`C) incubation for induction and synchronization of the acro-some reaction (AR) and the incubation time of spermatozoa in conventional SPA. Spermatozoa were collected from 18 patients, selected by the “swim-up” method and treated in three different ways: (1) short-term incubation group (SIG): 3 h incubation at 37 d`C, and (2) long-term incubation group (LIG): 20 h incubation at 37 d`C, and (3) low temperature group (LTG): 24 h incubation at 4d`C followed by additional incubation at 37 d`C for 3 h. The conventional methods of incubation, i.e. SIG (3 h) and LIG (20 h) did not show any significant differences as evaluated by the sperm penetration rate and the number of decondensing sperm heads per oocyte. In contrast, in the LTG all parameters were significantly increased, especially those of penetration rate (p < 0.0005) and decondensing sperm heads per oocyte (p < 0.0005). The percentage of AR significantly increased (p < 0.0005) in the LTG (14.7%) compared with SIG (6.1%) and LIG (10.6%). A significant correlation was demonstrated between AR and the parameters used for evaluation of the SPA. The penetration rate (Spearman test, r = 0.462, n = 54, p < 0.003) was the most significant parameter correlated with AR. It would appear that only human spermatozoa having completed AR are capable of fusing with the zona-free hamster ova. The use of low temperature to synchronize capacitation/AR may be particularly useful in the evaluation of so-called false-negative results in the SPA and provide a new way to evaluate the fertilizability of human spermatozoa.