Quantitative evaluation of ethane and n-pentane as indicators of lipid peroxidation in vivo.

The use of exhalation of ethane and n-pentane in experimental animals as parameters of lipid peroxidation led to an examination of pharmacokinetics of both compounds in rats. When rats were exposed, in a closed desiccator jar chamber, to a wide range of ethane concentrations, linear elimination pharmacokinetics were observed. n-Pentane, when concentrations higher than 100 ppm were applied, displayed saturation kinetics. These were formally explained by action of two competing metabolizing pathways or enzymes. Application of preexisting models could describe exhalation of both ethane and n-pentane by untreated control rats. Stimulation of lipid peroxidation by ferrous ions or by carbon tetrachloride resulted in dissimilar quantitative behaviours of ethane and n-pentane. Ethane production rates were enhanced after application of both compounds. Because of relatively slow metabolic eliminations this led to markedly elevated concentrations of ethane in the gas phase of the system. Pentane production rates were simultaneously enhanced. However, difficulties in interpretation arise because of rapid metabolic elimination of n-pentane. Compounds that diminish pentane metabolism are shown to evoke higher pentane concentrations in the system than compounds which only enhance the pentane production rate. Determinations of ethane exhalation should provide a more favourable parameter of lipid peroxidation than exhalation of pentane.