Differentiation of microsomal and cytosolic carboxylesterases in the rat liver by in vivo and in vitro inhibition.

We studied inhibition of rat tissue esterases by organophosphates and disulfiram, with special reference to hepatic microsomal and cytosolic carboxylesterases in vivo and in vitro. Hepatic microsomal carboxylesterase was strongly inhibited by disulfiram and bis-p-nitrophenyl-phosphate both in vivo and in vitro and by diisopropyl fluorophosphate in vitro, while cytosolic esterase was only slightly impaired. Pretreatment with phenobarbital did not affect the inhibition profiles of hepatic esterases in vitro. Based on these results, we conclude that hepatic cytosol of Wistar rats contains a soluble carboxylesterase that does not originate in the endoplasmic reticulum.