The simultaneous analysis of prostanoids in biological fluids by combined capillary column gas chromatography and negative-ion chemical-ionization mass spectrometry

Abstract

An enzyme system catalysing conversion of ethionamide into its sulphoxide was isolated and purified from liver homogenates from adult guinea pigs (Prema & Gopinathan, 1974). It was shown to have the characteristics of a microsomal monooxygenase, since stoichiometric amounts of 0, and NADPH were required for the reaction to take place. The enzyme contained FAD and non-haem iron, but cytochrome P-450 was not thought to be directly involved. Further investigation of this system (Hunt, et al., 1982) showed that sulphoxidizing capacity was also present in the cytosol and that the microsomal activity was associated with two different fractions, one of which appeared to involve the superoxide anion. Recent investigations in this laboratory have shown that, although the urinary excretion of cimetidine sulphoxide from adult guinea pigs dosed with cimetidine remains unchanged, the sulphoxidizing capacity of the microsomal fraction in vitro tends to decrease with increasing age of the animals. This suggests that there are at least two pathways for sulphoxidation in the guinea pig. The peaks of urinary sulphoxide excretion in the neonatal animal may therefore reflect activation of different systems that are able to catalyse the same reaction. As other substrate for S-oxidation are known to give similar twin peaks, this may be a general phenomenon in the guinea pig, presumably under hormonal control.