Determination of the rate of aldicarb sulphoxidation in rat liver, kidney and lung microsomes

Abstract

1. The rate of sulphoxidation of aldicarb (2-methyl- 2-(methylthio) propanal O-[(methylamino)carbonyl oxime], Temik®) in rat hepatic, renal and pulmonarymicrosomes was determined by quantitating the levels of aldicarb sulphoxide and aldicarb sulphone produced during incubations. Under in vitro experimental conditions used in the present study, aldicarb sulphoxide was the only metabolite produced, and further metabolism of aldicarb sulphoxide to aldicarb sulphone was negligible. 2. The average maximal velocity (μmol/min/mg protein) for the sulphoxidation of aldicarb, based on measurements of product formation, in liver, kidney and lung microsomes was 5·41, 39·51 and 2·45 respectively. The corresponding values for the Michaelis constant (μM) were 184, 1050 and 188 respectively. 3. These results imply that under in vivo conditions (1) aldicarb sulphoxidation is not likely to be saturable even at lethal doses in the rat, and (2) aldicarb clearance in rat liver and kidney will be limited by the rate of blood flow and not metabolizing enzyme levels.