Inhibition of acetaminophen sulfation by 2,6-dichloro-4-nitrophenol in the perfused rat liver preparation. Lack of a compensatory increase of glucuronidation.

The effectiveness of 2,6-dichloro-4-nitrophenol ( DCNP ) as an inhibitor of sulfation of acetaminophen, and the effect of DCNP on other conjugation reactions such as glucuronidation and glutathione conjugation were investigated in the once-through perfused rat liver preparation. The formation of glucuronide and glutathione conjugates of acetaminophen was insignificant under conditions when sulfation was suppressed either by the absence of inorganic sulfate or the presence of DCNP , suggesting that acetaminophen was a poor substrate for glucuronidation (high Km) and for the formation of the reactive metabolite leading to the formation of acetaminophen glutathione conjugate. DCNP was most effective in suppressing sulfation at low concentrations of acetaminophen, and the degree of inhibition increased with DCNP concentration, possibly due to a competitive mechanism of inhibition. Subsequent studies with tracer concentration of 3H-acetaminophen and 40 microM DCNP indicated that the steady state hepatic extraction ratio of acetaminophen decreased by 16%, sulfation was reduced by 19%, whereas glucuronidation increased by 28% in the presence of DCNP ; glutathione conjugation was not affected. Because acetaminophen is a poor substrate for glucuronidation and because glucuronidation remains a minor metabolic pathway in the biotransformation of acetaminophen, the changes in glucuronidation of acetaminophen with DCNP (28% above control value) failed to effect gross changes in acetaminophen disposition. Rather, the suppression of acetaminophen sulfation by DCNP is responsible for the decreased hepatic extraction of acetaminophen. This inhibition of acetaminophen sulfation by DCNP is readily reversible.