1. During anaerobic reductive incubation of liver microsomes, from either the pyridine- or phenobarbital-treated rat, with 1,1-dichloro-1-fluoroethane (HCFC-141b) in the presence of a NADPH-regenerating system, a time- and dose-dependent formation of reactive metabolites was detected as indicated by a depletion of added exogenous glutathione. 2. A statistically significant, dose-dependent loss of both cytochrome P450 and microsomal haem was also observed under these experimental conditions. Furthermore, a statistically significant decrease of p-nitrophenol hydroxylase and pentoxyresorufin O-depentylase activity was measured in microsomes from the pyridine- and phenobarbital-induced rat, respectively indicating that both P4502E1 and P4502B undergo substrate-dependent inactivation. 3. Both reactive metabolite formation and P450 inactivation were almost completely inhibited by previous bubbling of the incubation mixture with carbon monoxide, indicating that interaction of the substrate with a free and reduced P450 haem iron is required for substrate bioactivation and enzyme loss. 4. The presence in the incubation mixture of the spin-trap N-t-butyl-alpha-phenylnitrone (PBN) and the carbene trap 2,3-dimethyl-2-butene (DMB) largely prevented both glutathione depletion and P450 loss. This suggests that free radical and carbene intermediates formed by the metabolic activation of the substrate are involved in the inactivation of P450 and the loss of its prosthetic haem group.

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76 adult camel (30 males and 46 females) sera were surveyed for the normal activities of alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine phospho-kinase (CPK), gamma-glutamyl transpeptidase (GGT) and lactate dehydrogenase (LDH). The values recorded for the above enzymes were compared to other data in the literature.

Since norcotinine and 4-(3-pyridyl)-4-oxobutyramide (POBAM) are probable metabolites of nicotine and cotinine, it was of interest to investigate the further in vitro metabolism of these compounds. We now report our preliminary findings using rat microsomal preparations (induced and/or non-induced with phenobarbitone) fortified with NADPH. Following norcotinine metabolism, two compounds, i.e. the corresponding ketoamide (POBAM) and another product, were detected. The latter metabolite has an identical HPLC retention time as that of nicotinamide. Both metabolites showed identical UV spectra when compared to authentic compounds using a multi-array UV detector linked to a HPLC system. The structures of these metabolites were also confirmed by mass spectral analyses. The amount of POBAM was significantly increased when phenobarbitone induced rat microsomes was used. It indicates that the ketoamide is formed via a phenobarbitone inducible isozyme of CYP450. Following the metabolism of POBAM, two compounds, i.e. the corresponding acid (POBA) and an unidentified product, were detected. The uncharacterised compound had an identical HPLC retention time as nicotinamide. Both metabolites gave a UV spectrum identical to the authentic compounds. The detection of nicotinamide in incubates of norcotinine and POBAM suggests that it is released from NADP(H) by a stimulatory effect on glycohydrolase by the substrates. Further studies on the enzymology of these processes are in progress.