Aggregation of human sperm at higher temperature is due to hyperactivation

Chemotaxis of sperm cells to chemicals and hormones, such as progesterone, helps us to understand the concept of sperm transport. Here, the hypothesis was that heat increased sperm hyperactive motility, which caused the sperm to aggregate at the higher temperature. The objectives were (1) to determine the concentration of sperm at both halves of an artificial female reproductive tract made from a hermetically sealed cryopreservation straw filled with culture medium and placed with each end at different temperatures, and (2) to analyze the motility or kinematic parameters and hyperactivation of sperm found at the different temperatures. Cryopreserved- thawed human donor sperm (N = 6) were pooled and processed through 2-layer colloid solution. Analyses of the motile sperm were carried out and the washed sperm were homogeneously mixed and pipetted into several 0.5-mL French cryopreservation straws and heat-sealed. The control substance, consisting of acid-treated sperm, was also placed in several straws. The plastic straws of sperm were placed half at 23°C and half was at either 37 or 40°C. After 4 h, sperm at different sections of the straws were analyzed using the Hamilton Thorn motility analyzer (HTM-C). After 4 h of incubation, the concentration of sperm was doubled at the 40°C heated half of the straw when compared with the other half of the straw at 23°C. There were no differences in sperm concentration in the straw kept half at 37°C and half at 23°C. There were significantly higher percent motility, mean average path velocity, straight line velocity, lateral head displacement, and percent hyperactivation in sperm at the 40Γ temperature. The aggregation of sperm at the higher temperature of 40°C may be due to enhanced motility, increased sperm velocities, and a 10-fold increase in hyperactivation at that temperature. The 37°C temperature was not sufficient to attract sperm. Sperm cells migrating into the higher temperature site of ovulation begin nonprogressive hyperactivation movement, which is the physiological 'brake' to detain the sperm at the site of ovulation.