ABSTRACT
Cooling of mammalian sperms to 5 degrees C and subsequent heating to 30 degrees C causes alterations in the integrity of the plasma membrane producing acrosome disruption. This capacity of induction of acrosome reaction (AR) has allowed to evaluate this process in vitro, and has been correlated with induction of AR by follicular fluid and the percentage of in vitro fertilization. In this study, the time necessary to induce AR at 4 degrees C, the need of the increment in temperature to 37 degrees C, and the effect of glycerol to prevent the AR were evaluated. The sperms were selected by the Migration-Sedimentation technique, incubated in HTF and 1M glycerol at 4 degrees C and 20 degrees C for 1, 3, and 18 hours and then for 3 hours at 37 degrees C. The AR was determined by triple stain technique. Spermatozoa incubated by 18 hours at 4 degrees C increased the AR from 4.0% in the control (TO, post sperm selection) to 14.0% (p < 0.05). The subsequent incubation for 3 hours at 37 degrees C increased AR to 37.5% (p < 0.01 compared with 4 degrees C). The addition of 1M glycerol did not revert this effect. Our study confirms that the induction of AR with low temperatures requires long periods of incubation and a temperature increment to 37 degrees C. In addition, it is proposed that glycerol is not adequate for preservation of human spermatozoa at low temperature.