Studies on biliary excretion in the rabbit - I. The effect of icterogenin and rehmannic acid on bile flow and the excretion of bilirubin, phylloerythrin, coproporphyrin, alkaline phosphatase and bromsulphalein

Abstract

Several different plants are known which, when ingested by animals, cause hepatocellular damage and jaundice. Some, however, lead to icterus with minimal histological evidence of injury to the liver. From one such plant,Lippia rehmanni(family Verbenaceae), the active principle has been isolated and namedicterogenin. Icterogenin is a triterpene acid and is accompanied by smaller quantities ofrehmannic acidwhich has similar toxic action and a closely related chemical structure. Rehmannic acid also occurs inLantana camara. A technique is described of administering these substances intraperitoneally to rabbits provided with external biliary fistulae and of studying the changes which follow in the quantity and composition of the bile. Normal rabbit bile contains, among other constituents, bilirubin mono- and di-glucuronides, coproporphyrin, phylloerythrin and alkaline phosphatase. Suitable analytical methods have been devised for the quantitative determination of these. Bromsulphalein elimination in the bile after intravenous injection can be used as a sensitive test of hepatic excretory function in the rabbit. The type of conjugation which it undergoes has been studied. Rabbits with biliary fistulae have been given loading doses of either bilirubin, phylloerythrin, coproporphyrin or coproporphyrinogen and the elimination of these substances in the bile or urine has been followed. Only coproporphyrinogen is excreted, in part, by the kidney in the normal rabbit or animal with an external biliary fistula. Similar studies have been made with animals which had received icterogenin or rehmannic acid intraperitoneally in doses of 100 to 150 mg per kilogram. Some hours after administration of the drug, the volume of the biliary excretion diminishes markedly and the rate of elimination of bile pigment and the porphyrins falls to very low levels; alkaline phosphatase is affected to a much smaller degree. In extreme cases a ‘white bile’ devoid of pigment may result. Intravenously injected bilirubin, phylloerythrin, coproporphyrin or bromsulphalein given as loading doses at the height of the intoxication appear in the fistula bile in only minimal quantities, if at all, but each may be detected in the urine. That the failure of the icterogenin-poisoned animal to excrete bilirubin might be due merely to an interference with the hepatic enzyme systems effecting the conjugation of bilirubin with glucuronic acid seemed unlikely in view of the fact that bromsulphalein, which is conjugated with amino acids, and the porphyrins, coproporphyrin and phylloerythrin, which are normally excreted in the free form, are each similarly retained in the intoxicated animal. Direct evidence that an explanation of the inhibition of excretion must be sought rather in some general effect upon permeability of the liver cell was provided by the demonstration that intravenous injection of a rabbit bile rich in bilirubin conjugates into an icterogenin-poisoned animal was followed by complete retention of these pigments. Histological examination of the liver by conventional methods revealed no injury, apart from some vacuolation, which could be attributed to the action of the drugs. Some discussion is offered concerning the possible mechanism of this drug-induced intrahepatic biliary stasis and the relation which it may bear to clinical states encountered in human medicine.