Jaundice Glucuronyl transferase

In addition, there are some hepatic metabolic uses. Because hepatic glucuronyl transferase and the bilirubin-binding Y protein are increased by the barbiturates, phenobarbital has been used successfully to treat hyperbilirubinemia and kernicterus in the neonate. The nondepressant barbiturate phetharbital (A-phenylbarbital) works equally well. Phenobarbital may improve the hepatic transport of bihrubin in patients with hemolytic jaundice. 

Glucuronyl transferase (UDP-glncuronate biliru-bin-glucuronyltransferase) (EC 2.4.1.76). Enzyme completely absent. Severe jaundice and brain encephalopathy. Often death in infancy. Conjugation is obligatory for excretion of bilirubin. In a milder form of the disease some enzyme is present, and treatment is possible by administration of phenobar-bital, which stimulates hepatic uptake, conjugation and biliary secretion (as glucuronide) of bilirubin. 

There may be failure of the liver to conjugate bilirubin as in physiological neonatal jaundice. Another condition where this occurs is Crigler-Najjar syndrome where there is a deficiency of the glucuronyl transferase system. In these conditions, the bilirubin is mainly of the unconjugated variety. 

The fact that jaundice was noticeably absent in adolescents treated in a prophylactic manner with isoniazid, despite the occurrence of abnormal SGPT values, prompted Cohen and McNamara to investigate the effects of isoniazid on bilirubin metabolism (3 ) using rats as an experimental model. They found that hepatic bilirubin glucuronyl-transferase activity was enhanced in the animals receiving the drug. Such enhanced activity could account for the absence of hyperbilirubinaemia in subjects with biochemical evidence of hepatic dysfunction whilst receiving isoniazid. 

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