Action Spectrum for the Photodestruction of Bilirubin 1

Abstract

It was noted by Fischer and Herrle (1) in 1938 that bilirubin was susceptible to photo-destruction. He found that this reaction was dependent on the solvent and on the presence or absence of salts in the solvent. After 1957, this reaction was used as a clinical technique in the therapy of hyperbilirubinemia in the neonatal human (2, 3). It was felt that this therapy was probably less dangerous than the use of exchange transfusions to lower the serum bilirubin levels as it did not carry with it the dangers of hyper- and hypovolemia, electrolyte imbalances, and coagulation difficulties (4). Recent studies (5) have shown that this phototherapy is not entirely innocuous as it can destroy the retina of diurnal animals if the eyes are not adequately protected. Because the efficiency of the therapy could be increased without an actual increase in total energy output of the lights if only the exact wavelength for the photo-destruction of bilirubin were used, it was decided to investigate the action spectrum for the photodestruction of bilirubin.

Material and Methods. The experimental procedure consisted in dissolving between 3 and 7 mg/100 ml of bilirubin in plasma. Each such solution was divided into 15 aliquots of 3 ml each. The first aliquot was kept unexposed to light for the entire period of the experiment and the initial and final bilirubins of this sample were referred to as the 100% value for this bilirubin concentration. Each of the other aliquots was placed in a 10 by 10-mm cuvette and placed in the cell chamber of an Aminco-Bowman spectrofluorimeter for 1.5 hr. While in the cell chamber the sample was exposed to the light from a xenon arc lamp which had been monochromated by the spectrofluorimeter.