Stimulation of bilirubin formation in liver of newborn rats by fasting and glucagon.

Fasting in newborn Gunn rats caused an increase in serum bilirubin concentration and in liver bilirubin concentration and specific activity, and a significant stimulation of the heme catabolic enzyme, heme oxygenase, in liver. Treatment with glucagon enhanced conversion of newly formed endogenously prelabeled hepatic heme to bilirubin, with subsequent transfer of pigment to the circulation. Activity of heme oxygenase was increased in liver of hormone-treated newborns. These findings suggest that degradation of hemes from nonerythroid sources may play a role in hyperbilirubinemia association of hemes from nonerythroid sources may play a role in hyperbilirubinemia assiciated with hypoglycemia and caloric deficiency in newborn infants, and may contribute to elevated serum bilirubin levels in fasting adults.