Acrosome loss in human sperm incubated in vitro under capacitating conditions.

Human sperm were incubated under capacitating conditions and, at selected points up to 24 h of incubation, motile cells were fixed and assessed with the electron microscope for the presence or absence of the acrosome. Two methods of sample preparation were compared. In the first, semen samples were washed, incubated and filtered through glass beads to select motile cells before fixation. In the second, motile sperm were allowed to swim up into medium; this produced greater than 95% motile cells which were then incubated and fixed as required. In both series of experiments a significant increase in acrosome loss with time was observed (P = 0.00013), although only 10.5% of cells had lost the acrosome after 24 h. It is concluded that overt acrosome loss occurs less frequently in human sperm than in those of commonly used laboratory animals.