Effect of phototherapy on bilirubin excretion in man and the rat

Further evidence that the bilirubin excreted by Gunn rats during phototherapy is unconjugated is presented. The unconjugated bilirubin is not carried into bile as a water-soluble complex with rapidly excreted bilirubin derivatives, nor as a result of leakage of plasma protein into bile. Phototherapy does not augment biliary excretion of bilirubin in normal nonjaundiced rats, but does increase the concentration of conjugated bilirubin in the bile of patients with alcoholic cirrhosis, although their serum bilirubin concentrations are unaffected. The mechanism for augmented excretion of unconjugated bilirubin during phototherapy remains unexplained.