Effect of cooling on the motility and function of human spermatozoa

Human spermatozoa were cooled from 37 to 0 degrees C at 10 degrees C min(-1) in 5 degrees C steps with 1 min equilibration at each step, the temperature control was +/- 0.1 degrees C. Spermatozoa were held at 0 degrees C for 5 min and then rewarmed at the same rate. No significant effect of cooling on the straight-line velocity was found using computer-aided semen analysis. The physiological function of spermatozoa was also examined before and after cooling using hypoosmotic swelling, ionophore-provoked acrosome reaction, and binding to fragments of human zonae pellucidae. Spermatozoa were cooled either in seminal plasma or in conventional IVF medium with or without fractionation by centrifugation through a discontinuous Percoll gradient. When spermatozoa were cooled and rewarmed in seminal plasma there was no significant change in either the ionophore-induced acrosome reaction or the binding to zona pellucida fragments. When spermatozoa were fractionated by centrifugation through Percoll an increased response in both was seen. However, following cooling and rewarming, a significant decline in the response of both occurred. We suggest that motility alone is not a reliable predictor of changes in other physiological functions of spermatozoa following cooling. Furthermore, short-term cooling appears to have no significant detrimental effect on normozoospermic samples and cold shock may be avoided in the clinical context by controlled cooling and warming.