Activation of 14C-toluene to covalently binding metabolites by rat liver microsomes.

14C-Toluene was incubated with rat liver microsomes in the presence of an NADPH-generating system and metabolites were concentrated on cyclohexyl cartridges. The metabolites were separated by reverse phase HPLC and identified by comparing the retention time to standards. 14C-Toluene was converted to 14C-benzylalcohol, 14C-cresols, and an unidentified 14C-metabolite. Some of the radioactivity was found to bind covalently to microsomal macromolecules, preferentially to proteins. The binding was proportional to incubation time and microsomal protein concentration and required NADPH and molecular oxygen. The binding was greatly diminished when microsomes were heat denatured. The binding process was partially inhibited by carbon monoxide and SKF 525-A. When microsomes from phenobarbital- and 3-methylcholanthrene-treated rats were employed, binding was enhanced by 8- and 4-fold, respectively. The binding process was effectively diminished by the presence of reduced glutathione or cysteine in the incubation mixture and was not affected by lysine. Styrene oxide greatly enhanced binding. UDP-glucuronic acid, superoxide dismutase, and ascorbic acid also diminished the binding to some degree. It was concluded that toluene undergoes a hepatic microsomal monooxygenase-mediated activation, and the resultant reactive metabolites binds covalently to microsomal proteins.

A comparative study of the effects of benzene, toluene, and xylenes on their in vitro metabolism and drug-metabolizing enzymes in rat liver.

Male Sprague-Dawley rats were injected ip with benzene, toluene, or a mixture of xylene isomers at 20 mmol hydrocarbon/kg daily for 3 days. The effects of administration of these hydrocarbons upon their own in vitro metabolism, as well as upon cytochrome P-450, NADPH-cytochrome c reductase, aminopyrine N-demethylase, aniline hydroxylase, glutathione, glutathione S-transferase, and UDPglucuronyltransferase in liver were studied. Each hydrocarbon studied increased its own in vitro metabolism. Benzene had no effect on the metabolism of toluene or xylenes. Toluene and xylenes increased the metabolism of benzene, toluene, and xylenes. Cytochrome P-450 was elevated by toluene and xylenes, but was not affected by benzene. NADPH-cytochrome c reductase was induced by all three hydrocarbons. Aminopyrine N-demethylase and aniline hydroxylase were induced by toluene and xylenes and were not affected by benzene. Glutathione was elevated by benzene, decreased by xylenes, and not affected by toluene. Glutathione S-transferase was induced differentially by these hydrocarbons toward various substrates: toward 1-chloro-2,4-dinitrobenzene by benzene and toluene, toward 1,2-dichloro-4-nitrobenzene by benzene and xylenes, and no effect toward 1,2-epoxy-3-(p-nitrophenoxy)propane by any hydrocarbons. UDPglucuronyltransferase was induced by benzene and toluene when o-aminophenol and phenol were used as the substrate. Xylenes had no effect. Benzene was more effective at inducing conjugation enzymes. Xylenes were more effective at inducing cytochrome P-450 dependent enzymes. Toluene was equipotent at inducing both types of enzymes. The results indicate that the addition of methyl groups to the aromatic ring affects the inductive pattern of these monocyclic aromatic hydrocarbons.

Effects of Aroclor 1254 treatment on the in vitro hepatic metabolism of toluene, aniline and aminopyrine in hybrid sunfish.

The in vitro metabolism of the volatile aromatic hydrocarbon toluene by enzymes associated with the 12,000 g supernatant fraction of hybrid sunfish (Lepomis macrochirus X L. cyanellus X L. gibbosus) liver homogenates was studied. Aminopyrine demethylase (APDM) and aniline hydroxylase (AH) activities were measured. Intramuscular injections of Aroclor 1254 (a polychlorinated biphenyl) produced significant increases in APDM and AH activities (P less than or equal to 0.1, ANOVA). There were no significant changes in the metabolism of toluene, liver wet weights, or liver protein concentrations following treatment.

Renewal of opsin in the photoreceptor cells of the mosquito.

Mosquito rhodopsin is a digitonin-soluble membrane protein of molecular weight 39,000 daltons, as determined by sodium dodecyl sulfate gel electrophoresis. The rhodopsin undergoes a spectral transition from R515-520 to M480 after orange illumination. The visual pigment apoprotein, opsin, is the major membrane protein in the eye. Protein synthesis in the photoreceptor cells occurs in the perinuclear cytoplasm and the newly made protein is transported to the rhabdom. Light adaptation increases the rate of turnover of this rhabdomal protein. The turnover of electrophoretically isolated opsin is also stimulated by light adaptation. The changes observed in protein metabolism biochemically, are consistent with previous morphological observations of photoreceptor membrane turnover. The results agree with the hypothesis that the newly synthesized rhabdomal protein is opsin.

Changes in volume of the rhabdom in the compound eye of Aedes aegypti L.

The volume of the rhabdom in compound eyes of mosquitoes decreases upon illumination. This decrease is probably mediated by a bleaching of the visual pigment, since blue light is most effective in producing the change and red light is least effective. The reduction in rhabdom volume appears to be a result of rhabdomal membrane loss to coated vesicles and multivesicular bodies. These organelles were seen most frequently in blue adapted eyes, markedly less frequently in red adapted eyes, and only rarely in dark adapted eyes.

Vitamin A deficiency: effect on mosquito eye ultrastructure.

Mosquitoes (Aedes aegypti) were reared aseptically for one generation on an artificial diet containing neither vitamin A nor its usual precursor in animals, betacarotene. Function (electrical response to light) in the compound eyes of these animals was severely impaired. Ultrastructure of the photoreceptor cells was abnormal in two respects: multivesicular bodies were absent, and masses of smooth membrane lamellae were present near the nucleus. The organization of the photoreceptor organelle, the rhabdomere, was normal. The eyes of control mosquitoes, to whose diet beta-carotene was added, were functionally and structurally normal. Multivesicular bodies were normally abundant and the perinuclear membrane masses were not present.