Effect of incubating human sperm at room temperature on capacitation-related events

Abstract Objective: To determine the effect of human sperm incubation at room temperature (20°C) upon capacitation-related events. Design: Prospective study. Setting: Basic research laboratory. Patient(s): Semen samples were obtained from normozoospermic volunteers. Human follicular fluid (hFF) was collected from women undergoing assisted reproductive treatment. Intervention(s): Spermatozoa were incubated for up to 18 hours at 20°C and/or 37°C. Main Outcome Measure(s): Protein tyrosine phosphorylation patterns, development of hyperactivated motility, and induction of acrosome reaction (AR) in response to hFF. Result(s): Spermatozoa incubated for 18 hours at 20°C showed an array of tyrosine phosphorylated proteins similar to noncapacitated cells. After incubation at 20°C, the percentage of spermatozoa displaying hyperactivated motility and undergoing acrosomal loss in response to hFF was significantly lower when compared with cells kept the same time at 37°C. Conversely, spermatozoa incubated overnight at 37°C could respond to hFF, either at 37°C or 20°C. When preincubation at 20°C was followed by sperm exposure to 37°C, capacitation-related events could be activated. In capacitated cells (16 hours at 37°C), 2-hour incubation at 20°C led to a significant decrease in acrosome reaction inducibility, suggesting sperm decapacitation. Conclusion(s): Human sperm incubation at room temperature does not allow capacitation, although it does not affect hFF-induced acrosome reaction in capacitated cells. The blocking effect is overcome when spermatozoa are exposed to 37°C.