Abstract
The uptake, metabolism and toxicological implications of some inhaled halogenoalkanes have been investigated in the rat. In these experiments chlorinated alkanes of the series CX4, CHX3, CH2X2 and CH3CX3, where X = Cl or F have been used. The serial replacement of a chlorine by fluorine provided a means of comparison of uptake characteristics with metabolic activities that could be related to this substitution. A closed recirculating atmospheric exposure system was used and the depletion rate of chemicals from the atmosphere was monitored as uptake and metabolism proceeded. After the exposure, the concentration of total glutathione and glutathione disulphide (GSSG) in liver and lung, and selected serum enzyme activities were determined. The results were correlated with the physico-chemical properties of the compounds - molar polarizability (amol), activation energy (ΔE), and partition coefficient (log P). The rate of uptake of chemicals decreased with increased fluorine content and correlated directly with calculated log P and amol. None of the compounds studied depleted total glutathione in lung or increased GSSG in liver or lungs. Total glutathione depletion was observed in liver with the compounds CCl4, CHCl3, CHF3, CH2Cl2, CH2Cl2, and all the CH3CX3 series. There were neither changes in serum enzyme activities nor observable damage in liver or lung in all rats exposed to all compounds except for CHCl2F. For this compound, raised sorbitol dehydrogenase activity was recorded in sera of rats either 2 or 24h after exposure and was consistent with histologically observable changes in liver. In in vitro experiments with hepatic microsomal fractions from rats pretreated with phenobarbitone, all compounds showed type I binding spectra. The binding affinity for hepatic P450 (Ks) was greatest with compounds with high chlorine content and varied inversely with calculated log P except for the CHX3 series. For this series, the lowest Ks value was recorded for CHF3. A positive linear relationship was established between log Ks values and log P for all compounds. Upon incubation of the compounds under aerobic conditions with hepatic microsomes from rats pretreated with phenobarbitone, a NADPH generating system and reduced GSH, only CHCl3, CCl4 and CCl3F depleted GSH. Spectral peaks were recorded with either sodium dithionite- or NADPH-reduced microsomal fractions and the compounds under investigation at either 444-450nm or 415-418nm respectively. Under anaerobic conditions, CH3CCl3, CH3CCl2F, CH2Cl2, CH2FCl, CHCl3, CHCl2F, CHF3, CCI4, CCl3F showed marked GSH depletion when incubated with GSH, NADPH generating system and hepatic microsomes from rats pretreated with phenobarbitone which suggests a reductive metabolic pathway for these compounds and formation of reactive intermediates.