Temporal changes in motility parameters related to acrosomal status: identification and characterization of populations of hyperactivated human sperm

The occurrence and time course of capacitation, acrosomal loss, and hyperactivated motility require quanti-tative definition in order to characterize fertile human sperm. In this study, video microscopy and digital image analysis were used to measure curvilinear (VCL) and straight line (VSL) velocity, average linearity of progression (UN [100 x VSL/VCUJ), maximum and mean amplitude of lateral head displacement (ALH), beat-cross-frequency (BCF), DANCE (VCL x meanALH) and DANCEMEAN (meanALH/(UIN/100)). These parameters were mea-sured for sperm in semen and in the swim-up fraction of washed cells during incubation for up to 24 h under in vitro fertilization (IVF) conditions. Acrosomal loss was monitored in the same population of washed cells by an immunofluorescence end-point assay. The greatest increase in mean values of motility parameters was observed when seminal sperm were washed free of seminal plasma. Increases continued for up to 6 h of incubation. Two subpopulations of hyperactivated sperm were identified; one type, not found in semen, showed star-spin trajectories, and constituted 3.0, 3.8, 4.5, and 4.1 % of the swim-up population after 0, 3, 6 and 24 h of incubation. The second type, termed transitional showed a more progressive trajectory and constituted less than 1 % in semen. In total, hyperactivated cells constituted 0.8 % of cells in semen, 14.5 % of the swim-up population with no incubation, and 23.1, 22.7, and 19.4 % after 3, 6, and 24 h of incubation, respectively. Acrosomal loss in the swim-up population was delayed during the first 3 h of incubation, then increased from near 5 % at 3 h to 7 and 12 % at 6 and 24 h, respectively. The kinetics of change in the extent of hyperactivation and in acrosomal loss, although measured in different cell populations, are consistent with an association between these two events