Enhanced fertility after heat-induced hyperactivation.

OBJECTIVE

To determine sperm hyperactivation, kinematic parameters, and fertilizing capacity after pretreating sperm at 40 degrees C for 4 hours.

DESIGN

Prospective study involving pooled donor sperm that were colloid washed and incubated at either 23 degrees C (control) or 40 degrees C (heat-treated) for 4 hours as pretreatment. After incubation, analyses were performed with a computer-assisted sperm analyzer, whereas separate portions of sperm were evaluated with the sperm penetration assay at 37 degrees C.

SETTING

Clinical and academic research environment.

PATIENT(S): Cryopreserved-thawed sperm from different donors (n = 5).

MAIN OUTCOME MEASURE(S): Sperm kinematic and fertilizing parameters.

RESULT(S): Heat pretreatment of sperm resulted in over 22 times higher hyperactive motility at hour 4 compared with the control. The other kinematic parameters were also different. The heat-pretreated sperm group had a significantly higher percent penetration of zona-free oocytes with more swollen sperm heads per oocyte and enhanced sperm binding.

CONCLUSION(S): The results showed that hyperactivation was induced by pretreatment of sperm with 40 degrees C heat, suggesting the involvement of heat factors in hyperactivation. The fertilizing capacity of sperm may be improved by the mild heat pretreatment when marked by the presence of heat-induced hyperactivation.