Effect of freezing method on chromatin integrity and morphology of human spermatozoa from fertile and subfertile men

37 semen samples obtained either from patients attending our Andrology and IVF unit for treatment (n=15) or from donors with proven fertility and norm al sperm quality according to WHO guidelines (1992) (n=22). Each semen samp le was divided into two parts after liquefaction and addition of cryoprotec tant (1/ 1, vol/ vol) ( test yolk buffer, Irvine Scientific). The first par ts was frozen by using programmed biological freezing machine (Planer serie 10) and the second part was frozen by means of liquid nitrogen vapour. Sme ars were made from each aliquot before and after freeze thawing procedure f or morphology assessments (Strict criteria) and chromatin condensation (ani line blue staining). The mean percentage of chromatin condensed spermatozoa in the semen samples obtained from donor (control group) before freezing was 88.2% +/- 7.9% and decreased significantly (p<0.0001) to 80.7% +/- 6.6% after freeze-thawing with programmed biological freeze and to 78.9% +/- 7.3% by using liquid nit rogen vapour (p<0.0001). The corresponding value for semen obtained from pa tients was 72.3% +/- 10.8% before freezing and decreased to 64. 1% +/- 9.7% and 62.2% +/- 9.6% respectively (p<0.001). On the other hand, the mean per centage of morphologically normal spermatozoa (control group) decreased fro m 27.6% +/- 6.5% before freezing to 23.4% +/-4.9 % (p<0.0001) after freeze- thaw with biological freezer and to 23.4% +/- 5.3% (p< 0.0001) after freeze -thaw with liquid nitrogen vapour. Besides, in the patients group the cryoi njury was higher than that in the control group. The mean percentage of mor phologically normal spermatozoa decreased from 15.1% +/-6.5 % to 12.1% +/- 6.5% by freezing with the aid of biological freezer and to 11.0% +/- 4.8% b y using liquid nitrogen vapour. In conclusion: This study demonstrate that chromatin packaging and morphology of human spermatozoa decrease significan tly after freeze-thawing process in comparison to native semen sample not o nly by freezing with liquid nitrogen but also by freezing with programmed f reezer. On the other hand, the semen samples with initially good quality (d onor sperm) withstand the freeze thaw injury better than those initially wi th subnormal semen quality. Therefore, the programmed biological freezer co uld be however, recommended for freezing subnormal semen samples in order t o avoid further damage to spermatozoa chromatin structure.