Glutamic-oxalacetic transaminase leakage from human spermatozoa as an indicator of cryodamage

The levels of extracellular glutamic-oxalacetic transaminase (GOT: EC 2.6.1.1) activity have been measured in cell-free supernatants of human semen and of semen + cryoprotectant mixtures both before freezing by either cryostorage or quench-freezing regimes, and after subsequent thawing. The mean level of GOT activity in seminal plasma was 293 (+/- 15 sem) IU/l at 37 degrees C, this being 15 times the level in normal blood plasma. Seminal GOT is positively correlated (p less than 0.001) with the sperm density. Increases in the extracellular GOT activity were measured after both cryostorage and quench-freezing, but the latter procedure, which destroys all sperm motility, caused an average of 2.8 times more enzyme release than cryostorage. Although the release of GOT from human spermatozoa during freezing and thawing does not correlate with the commonly used percent return of motility as an estimate of cryosurvival, possible explantations for this finding, and its importance, are discussed. Objective measurements such as GOT release may be developed to augment, if not replace, subjective estimations of sperm motility as indicators of cellular integrity in studies of sperm cryostorage.