Species variation in toxication and detoxication of acetaminophen in vivo: a comparative study of biliary and urinary excretion of acetaminophen metabolites.

Acetaminophen (AA) is converted to a toxic electrophile that may subsequently form a glutathione conjugate (AA-GS). In addition to the toxication pathway metabolites, which consist of AA-GS and its hydrolysis products (AA-cysteinylglycine, AA-cysteine and AA-mercapturate), detoxication pathway metabolites, such as AA-glucuronide and AA-sulfate, are also formed. In order to evaluate the role of these opposing pathways in the reported species variations in susceptibility to AA-induced liver injury, AA was administered to hamsters and mice, species which are susceptible to AA-induced liver injury, and to rats, rabbits and guinea pigs, species which are relatively resistant to AA-induced liver injury, and the biliary and urinary excretion of AA metabolites were measured simultaneously for 2 hr after administration of AA (1 mmol/kg i.v.). The AA-susceptible species excreted 27 to 42% of the dose as toxication pathway metabolites, whereas the resistant species excreted only 5 to 7% of the dose as toxication pathway metabolites. Most of the toxication pathway metabolites appeared in bile, where their composition reflected hepatic gamma-glutamyltranspeptidase activity; hamsters and mice (low gamma-glutamyltranspeptidase activity) excreted mainly AA-GS, whereas bile from rabbits and guinea pigs (high gamma-glutamyltranspeptidase activity) contained significant amounts of AA-GS hydrolysis products. Thus, the biliary excretion of AA-GS and its hydrolysis products may be used as an index of toxic activation of AA. The excretion of the detoxication pathway metabolites (AA-glucuronide and AA-sulfate) was 74, 62, 41, 27 and 12% of the dose in guinea pigs, rats, mice, rabbits and hamsters respectively.(ABSTRACT TRUNCATED AT 250 WORDS)