Factors Influencing the Microsomal Metabolism of ³H-Reserpine

Abstract

The hydrolysis of ³H-reserpine and the subsequent formation of ³H-trimethoxybenzoic acid (TMBA) were examined. ³H-reserpine disappearance and ³H-TMBA formation were determined by a combination of solvent extraction and thin-layer chromatography. Subcellular fractionation experiments indicated that the greatest amount of hepatic reserpine metabolizing activity was found in the microsomal fraction. This fraction could be stored for up to 14 days at –20 °C without appreciable loss in enzyme activity. Reserpine metabolism was both temperature and pH sensitive with the greatest rate of biotransformation occurring at 37 °C and at a pH of about 7. An NADPH generating system was essential for optimal enzyme activity since metabolism did not occur in the absence of such a system. Both SKF 525-A and carbon monoxide inhibited the metabolism of reserpine. Pretreatment with either phenobarbital or 3-methylcholanthrene did not result in increased hydrolysis activity in either male or female rats. ³ H-reserpine metabolism was reduced by co-incubation with meperidine and possibly with lidocaine and procaine, while succinylcholine had no effect. Species’ differences in reserpine’s metabolism were noted with the mouse and rat showing the greatest hydrolyzing activity followed by the dog, cat and guinea pig.