Objectives: To assess (1) the effect of increased lipid peroxidation on sperm membrane damage that occurs during the freeze-thaw process of cryopreservation; (2) the effect of sperm concentration on lipid peroxidation in normal fertile men; and (3) the relation between sperm motility, morphology, and lipid peroxidation.
Methods: Lipid peroxidation was measured as levels of malonaldehyde by the thiobarbituric acid method. Malonaldehyde levels in fresh and frozen-thawed semen specimens from normal donors (n = 20) were compared at a sperm concentration of 20 x 10(6)/mL. Sperm concentrations of 5, 10, 20, and 40 x 10(6)/mL were used to assess the effect of sperm concentration on malonaldehyde levels in frozen specimens. A computer-assisted semen analyzer was used to analyze sperm concentrations and motility. Comparison of the effect of TEST-yolk buffer, glycerol, and Ham's F-10 buffer on lipid peroxidation was studied in fresh semen from normal fertile men (n = 5).
Results: Malonaldehyde levels did not differ between fresh and cryopreserved semen specimens (P = 0.99). There was no difference in malonaldehyde levels from TEST-yolk buffer, glycerol, and Ham's F-10 buffer. As sperm concentrations increased, so did malonaldehyde levels, from 1.21 +/- 0.05 nM/hr at 5 x 10(6)/mL to 3.50 +/- 0.46 nM/hr at 40 x 10(6)/mL (P = 0.000007). Sperm motility, morphology, and malonaldehyde levels in freeze-thaw specimens were not correlated before or after removal of the cryoprotective medium.
Conclusions: Malonaldehyde levels do not differ between fresh and frozen semen in normal men. Cryopreservation-induced membrane damage is not related to lipid peroxidation but may be associated with stress induced during freezing and thawing. Malonaldehyde levels increase as sperm concentrations increase. There is no correlation between sperm motility, morphology, and malonaldehyde levels.