The production of hydrogen peroxide (H(2)O(2)) was investigated by means of cytochemical reaction with cerium chloride in human embryos cryostoraged for a long time period. The sites of H(2)O(2) generation were demonstrated at submicroscopic level in both freshly thawed embryos and in embryos and blastocysts formed after subsequent culture. The intact blastomeres as well as cells of well developed blastocysts did not produce any H(2)O(2). Two main intracellular sites of H(2)O(2) production were identified: mitochondria and plasma membranes. Some alterations and often destruction of plasma membrane integrity accompanied by massive H(2)O(2) generation are believed to be caused by the freezing and thawing.

Department of Histology and Embryology Masaryk University in Brno Faculty of Medicine Czech Republic