HUMAN SPERMATOZOAL TAIL HYPOOSMOTIC SWELLING TEST, MOTILITY CHARACTERISTICS IN HYPOTONIC SALINE, AND SURVIVAL OF SPERMATOZOA AFTER CRYOPRESERVATION

Normozoospermic semen samples (n = 82) were examined to investigate wh ether the degree of sperm tail swelling in hypo-osmotic medium (fructo se and sodium citrate; 150 mOsm/l), and motility characteristics after a 15-min exposure to hypotonic saline (sodium chloride; 150 mOsm/l) c ould predict the cryosurvival rate (% post-thaw motility/% pre-freeze motility X 100%) of spermatozoa after cryopreservation by the liquid n itrogen vapour freezing method using the TEST-glycerol-egg yolk buffer . The CellSoft automated semen analyser was used to analyse sperm moti lity in pre-freeze and post-thaw semen samples, and after exposure to hypotonic saline. Sperm tail hypo-osmotic swelling and sperm motility in pre-freeze semen showed no significant correlations (P > 0.05) with the cryosurvival rate. There were significant correlations (P < 0.05) between the cryosurvival rate and the following sperm motility parame ters in hypotonic saline: % motility (r = 0.2846), motility index (% m otility X curvilinear velocity; r = 0.2809) and % decrease in motility index from the baseline value in semen (r = 0.3378). The % decrease i n motility index after hypotonic saline treatment was significantly le ss (P < 0.05) in the normal (greater-than-or-equal-to 50% cryosurvival rate; mean +/- SEM 5.9 +/- 3.2%; n = 33) compared with the subnormal (< 50% cryosurvival rate; 27.3 +/- 4.8%; n = 49) cryosurvival groups. This parameter was also determined, by multivariate discriminant analy sis, to be capable of classifying each pre-freeze semen sample into ei ther cryosurvival group with 69.5% accuracy. These results indicate th at cryosurvival of spermatozoa is not dependent on pre-freeze motility characteristics, and that results of the tail hypo-osmotic swelling t est cannot be utilized to predict the susceptibility of human spermato zoa to cryoinjury. Studies on the motility characteristics in an artif icial medium such as hypotonic saline, while unable to provide a power ful predictive assay, may help to provide useful information about the survival of human spermatozoa after cryopreservation.