The metabolism of naphthalene and 1-naphthol by houseflies and rats

Gastrointestinal metabolism and transport of pesticidal carbamates

Published evidence pertaining to gastrointestinal absorption and metabolism of pesticidal carbamates will be reviewed. The major body of evidence will come form investigations conducted by the author on N-methylcarbamate pesticides with rats; few investigations directly involving the gastrointestinal system have been reported by other research groups. Results derived from in vitro and isolated in vivo preparations show that pesticidal carbamates are absorbed and metabolized by gastrointestinal tissues. Numerous gastrointestinal metabolites have been separated; some have been identified and their behavior in the gut characterized; these data will be included in the review to the extent they have been published. The absorptive and metabolic capacities of the gastrointestinal system vary from one region to another. The author draws from evidence obtained from in vitro and in vivo studies and proposes the events that occur between carbamate ingestion and the appearance of the compound and/or its metabolites in the portal blood or mesenteric lymph. In this endeavor, the author acknowledges that superimposition of the metabolic precursory substrate-product sequence on the sequential physiologic steps from ingestion to defecation produces a complex situation which is difficult if not impossible to study meaningfully by investigation of one tissue component at a time (i.e., epithelial uptake, epithelial metabolism, mucosal to serosal transport, etc.).

Metabolism of radiolabeled insecticides in insects and related arthropods: a critical study of various techniques

The metabolism of radiolabeled insecticides in insects and acarina is studied largely by coupling radiotracer techniques with analytical methods, such as TLC, paper and column chromatography, gel-permeation chromatography, and enzymatic assays. These techniques in various combinations yield both the identification and quantification of the metabolites. Other analytical methods such as gas chromatography or IR spectrometry may also be used to obtain additional support for identification of metabolites. In the absence of authentic chromatographic standards, however, NMR and mass spectrometry are necessary in the identification of the unknown compound. The quantity of the radiolabeled insecticide administered should be within the toxicological range of the insect. Therefore, the dosage-mortality response of the insect using unlabeled material should be determined. A dose should be selected that keeps insect mortality to a minimum in order to avoid complications in the computation of the balance data. The radiolabeled insecticide is usually applied topically to the insect. Alternately, the material may be administered by dipping in a solution containing the radiolabeled compound or by exposure to filter paper impregnated with radiolabeled material. Administration of the radiolabeled material by the oral route presents several problems. Sterile rearing conditions are mandatory to avoid contamination of treated diet with microorganisms. Some knowledge of the insect's feeding rhythm is desirable so that the labeled diet is given at peak feeding time. Synthetic diets should be adjusted to pH 7.0. These precautions minimize degradation of the insecticide in the diet prior to consumption by the insect. Precise doses of radiolabeled materials may be administered by injection. The technique is mainly useful in metabolism studies of intermediate materials resulting from the biotransformation of the parent compound.

Biological and nonbiological modifications of carbamates

Methylcarbamate insecticides undergo hydrolysis, oxidation, dealkylation, and conjugation in animals, plants, and insects to form similar or identical products. Carbaryl is hydroxylated in biological systems to form hydroxy, dihydro-dihydroxy, and N-hydroxymethyl carbaryl and is hydrolysed to form 1-naphthol. The products are conjugated, stored, or excreted. Carbofuran is hydroxylated at the 3 position and propoxur at the 5 position to form hydroxylated derivatives. N-hydroxymethyl derivatives of these two carbamates may also be formed. Hydrolysis appears to be the major metabolic pathway of carbofuran in the animal. Aldicarb is oxidized to its sulfoxide and then hydrolysed to the oxime sulfoxide in animals and plants. Plants hydrolyse the oxime sulfoxide to form the corresponding aldehyde, which is an intermediate in the formation of 2-methyl-2-(methyl-sulfinyl)propanol. Methomyl, which is structurally similar to aldicarb, is metabolized in plants to acetonitrile, carbon dioxide, and methylamine. Bux and Meobal undergo hydrolysis and hydroxylation to form N-hydroxy methylcarbamates, as well as hydroxybutylphenyl and hydroxymethylphenyl methylcarbamates. Zectran, which contains a dimethylamino group, is converted to the methylamino, amino, and methylformamido derivatives by insects and plants. In soil and water, methylcarbamate insecticides are hydrolysed to their respective phenols or oximes.

Carbamate resistance in mosquitos. The metabolism of propoxur by susceptible and resistant larvae of Culex pipiens fatigans

Toxicity tests on Culex pipiens fatigans with propoxur (o-isopropoxyphenyl methylcarbamate) and carbofuran (2,2-dimethyl-2,3-dihydrobenzofuranyl-7-methylcarbamate) indicated that both compounds are fast-acting insecticides. Transfer of treated larvae to fresh water results in their partial recovery from knockdown.Propoxur is metabolized by resistant and susceptible larvae by their homogenate-reduced nicotinamide-adenine dinucleotide phosphate (NADPH(2)) enzyme system and by the microsome-plus-soluble fraction of mouse-liver extracts to at least 10 organosoluble metabolites with the isopropoxy group intact. The major metabolites, which are primarily hydroxylation products or the result of degradation of these products, have tentatively been identified as: acetone plus o-hydroxyphenyl methylcarbamate, 2-isopropoxy-5-hydroxyphenyl methylcarbamate, 2-isopropoxyphenyl carbamate, and 2-isopropoxyphenyl N-hydroxymethylcarbamate. Upon incubation of water-soluble products from treated larvae with beta-glucosidase, beta-glucuronidase, aryl sulfatase and acid phosphatase, the conjugates are hydrolysed, liberating mainly hydroxylated carbamates.The results indicate that slower absorption as well as faster detoxification by hydroxylation mechanisms, together with conjugation with polar molecules and elimination, are major factors in resistance of mosquito larvae to substituted-aryl methylcarbamate insecticides.

The conjugation of phenols with phosphate in grass grubs and flies

1. Houseflies, blowflies and New Zealand grass grubs were dosed with 1-naphthol, 2-naphthol or p-nitrophenol. 2. The corresponding monoaryl phosphates were identified in extracts of insects or excreta along with the beta-glucosides and ethereal sulphates of the phenols. 3. No diaryl phosphates or glucosiduronates were detected but an unidentified metabolite of [(14)C]1-naphthol was present in extracts of flies dosed with [(14)C]1-naphthol.