Evaluation of cryoinjury of spermatozoa after slow (programmed biological freezer) or rapid (liquid nitrogen vapour) freeze-thawing techniques.
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PURPOSE: This study was initiated to determine the negative effect (cryodamage) on human spermatozoa after freeze-thawing and to find out whether freezing of spermatozoa with a computerized biological freezer is more advantageous than freezing above static liquid nitrogen vapour with regard to spermatozoa vitality, chromatin normality, morphology, and membrane integrity. METHODS: Forty-four semen samples were obtained from patients attending andrology laboratory, and each sample was divided into two aliquots. One aliquot was frozen using static liquid nitrogen vapour (G.II) and the second with a computerized biological freezer (G.III). Acridine orange was used for assessment of chromatin cryoinjury, whereas the morphology was evaluated according to WHO criteria. Hypoosmotic swelling test was used to identify membrane integrity and eosin-nigrosin staining was used to determine the vitality of spermatozoa. RESULTS: The mean percentage of normally condensed chromatin in the native semen sample (G.I) decreased significantly (p < .001) after freeze-thawing by using either liquid nitrogen vapour (G.II), or a biological freezer (G.III), which was significantly higher (p < .001) after freezing with liquid nitrogen vapour than after freezing with the biological programmed freezer. Morphologically normal spermatozoa decreased significantly (p < .001) in both freezing methods in comparison to the native semen samples. In addition, membrane integrity of spermatozoa (HOS-test positive) was significantly lower (p < .001) after the freeze-thawing procedure in G.II and G.III compared to G.I. In both these parameters the deterioration was similar among the two freezing procedures. Finally the mean percentage of live spermatozoa decreased significantly (p < .001) in both freezing techniques in relation to the mean value in the neat semen samples. CONCLUSIONS: Freeze-thawing procedure has a detrimental effect on chromatin, morphology, membrane integrity, and vitality of human spermatozoa not only by freezing above static liquid nitrogen vapour but even by using a computerized biological freezer. However, the chromatin deterioration rates are significantly higher by freezing above static liquid nitrogen vapour in comparison to freezing with a programmed biological freezer. Therefore, we recommend the use of this technique for freezing semen especially when ICSI technique is considered as the main therapeutic procedure.
