THE ROLE OF BILIRUBIN ON EXERCISE-INDUCED OXIDATIVE STRESS

Abstract

Bilirubin has been considered to be useless and harmful in vivo. Previous studies have reported that the urinary excretion of biopyrrin, a biomarker of oxidative bilirubin metabolites, increases by endotoxin shock or ischemia/reperfusion. Although it has recently been suggested that bilirubin functions as a free radical scavenger in vivo, there are no studies to investigate whether urinary excretion of biopyrrin is increased by exercise. PURPOSE In this study, we investigated the effect of an acute bout of running exercise on urinary excretion of biopyrrin. METHODS Six healthy male volunteers (21.0 ± 0.6 yrs) have performed treadmill running for 30 min at an intensity corresponds to 80% maximum oxygen uptake under two conditions:N-acetyl-cysteine supplemented (NAC) and placebo control (Cont) conditions. Blood samples were obtained before and immediately after the exercise. Urine sample was collected continuously for 24 hours before and following the exercise. RESULTS Serum lactate dehydrogenase (LDH) activities in both Cont and NAC were significantly increased after the exercise compared with respective initial levels (p < 0.001). Significant increases of serum creatine phoshokinase (CPK) activities from initial levels were shown only in NAC (p < 0.05). Significant decreases in serum thiobarbituric acid reactive substances (TBARS) and increases in urinary excretion of biopyrrin from initial resting levels were observed only in Cont (p < 0.05). No significant differences were found between Cont and NAC for LDH, CPK and TBARS after exercise. However, urinary excretion of biopyrrin during 24 hours after the exercise was significantly inhibited by NAC administration (p < 0.05). CONCLUSION These results indicate that bilirubin is one of the antioxidant to scavenge free radicals generated by exercise. It is suggested that measurement of biopyrrin level in urine may be useful biomarker for predicting the degree of oxidative stress by exercise.