Effect of jaundice phototherapy on intestinal mucosal bilirubin concentration and lactase activity in the congenitally jaundiced gunn rat

The effect of phototherapy on intestinal mucosal bilirubin concentration and lactase activity in the Gunn rat was studied. Ten groups of six or seven animals each were studied. Heterozygous (Jj) and homozygous (jj) animals were given 24, 48, or 72 hr of continuous phototherapy, and Jj and jj animals were given 24- and 48-hr sham control treatments. Phototherapy reduced serum bilirubin concentration by 53% at 24 hr, 59% at 48 hr and 68% at 72 hr. The mucosal concentration of bilirubin appeared to parallel the declining serum concentration and was lower in treated than in control jj animals. The jejunal and ileal lactase activity, expressed per mg protein, was not depressed by phototherapy. The lactase activity of jejunum and of ileum of treated jj as compared to treated Jj and control jj at 24 and 48 hr and as compared to treated Jj at 72 hr was never reduced; i.e., jejunal lactase activity in jj treated for 72 hr was 15.1 ± 4.2 (x ± S.D.) units/g protein as compared to 16.2 ± 4.2 for Jj treated for 72 hr and 12.0 ± 4.2 for jj 48-hr control animals. The ratio of lactase to sucrase activity demonstrated a significant increase in lactase activity relative to sucrase in all animals treated for 48 or 72 hr. This latter effect is potentially due to alteration in the circadian rhythm while under constant irradiance. These data convincingly demonstrate that the Gunn rat does not develop lactase deficiency consequent to phototherapy. Speculation: These data support the hypothesis that acute intestinal secretion is important in the mechanism of diarrhea occurring during jaundice phototherapy by arguing against the role of lactase deficiency in that mechanism.