Abstract

• The effectiveness of phototherapy in the treatment of neonatal hyperbilirubinemia is so established that it is widely used without serious side effects. The widespread use of phototherapy has caused some concern since substances other than bilirubin may be photocativated or photodecomposed. The toxic properties of these photoactivated substances might prove to be more harmful to the neonatal infants than bilirubin. The purpose of the present study was to investigate the photodynamic metabolic effects on the hepatic microsomal cytochrome P-450, cytochrome b₅, riboflavin status, hepatic microsomal DNA and RNA of newborn rats at 1 week and 3 weeks of illumination by phototherapy lights. The results are as follows: 1) Activities of hepatic microsomal cytochrome P-450 and cytochrome b_5 in newborn rats increased significantly at 3 weeks of illumination by phototherapy lights. 2) Induced cytochrome P-450 by phototherapy lights increased the ring-hydroxylation of AAF. more significantly(P<0.001) than the N-hydroxylation(P<0.01). 3) Erythrocyte glutathione reductase activity coefficient as a measure of riboflavin status increased significantly(P<0.05) at 1 and 3 weeks of illumination by phototherapy lights, and this means the riboflavin deficiency due to the photodecomposition of riboflavin by phototherapy lights. 4) The quantative measurement of hepatic microsomal DNA and RNA showed no significant change by phototherapy lights.