Background: The purpose of our study was to investigate the influence of low-dose heparin on peroxide levels and the antioxidant activity of superoxide dysmutase (SOD), catalase (CAT), and glutathione
peroxidase in the red blood cells of patients undergoing minor abdominal surgery.
Material/Methods: 49 patients scheduled for open cholecystectomy, with a median age of 43, were randomly assigned to either the heparin group (HG) or the placebo group (PG). HG patients received a
subcutaneous dose of 100 IU/kg body weight of standard heparin for 6 days, beginning the first day after surgery. On the day prior to surgery and on the 1st, 2nd and 6th postoperative days, blood samples from peripheral veins were collected, and the levels of peroxides, superoxide dysmutase (SOD), catalase (CAT) and glutathione peroxidase activity in the hemolysate of red blood cells were determined. The level of malondialdehyde was also measured.
Results: Significantly lower levels of peroxides, as well as higher antioxidant activity of SOD and CAT, was found in the erythrocytes of HG patients. Heparin administration did not significantly influence the activity of glutathione peroxidase. There were also no differences in the levels of malondialdehyde between HG and PG patients.
Conclusions: Low-dose standard heparin administered subcutaneously in patients undergoing minor abdominal surgery shows an antioxidant effect. Further studies are required to clarify the mechanism of increased SOD and CAT activity in red blood cells induced by heparin.

Keywords: Anticoagulants - pharmacology, Catalase - blood, Catalase - metabolism, Cholecystectomy, Erythrocytes - enzymology, Glutathione Peroxidase - blood, Heparin - pharmacology, Malondialdehyde - metabolism, Oxidative Stress - drug effects, Peroxides - blood, Postcholecystectomy Syndrome - blood, Superoxide Dismutase - blood, Time Factors