T. R. Fukuto

The effects of cholinergic substances upon the isolated heart of Periplaneta americana

Abstract The effects of acetylcholine and twelve other structurally related esters in accelerating the heartbeat rate of the isolated heart of Periplaneta americana were studied. Acetylcholine was about forty times more effective than acetylthiocholine or any other analogues studied, indicating that the receptor sites are much more stereospecific than the active site of insect cholinesterase. Organophosphorus and phenyl N-methylcarbamate anticholinesterase at great dilutions also accelerate the rate of heartbeat. The importance of the acetylcholine cholinesterase system at the insect neural synapses is emphasized by the protective action afforded by pyridine aldoxime methiodide and atropine sulphate in antagonizing the action of the anticholinesterases on heartbeat rate.

Penetration and comparative metabolism of leptophos in susceptible and resistant houseflies

The metabolism and rate of penetration of leptophos (O-methylO-4-bromo-2,5-dichlorophenyl phenylphosphonothioate) was determined in a susceptible strain and a strain of houseflies which was 50-fold resistant to leptophos. Penetration of leptophos into resistant flies was substantially slower than into susceptible flies but large differences in metabolism, both quantitatively and qualitatively, were not observed. No difference was observed in the sensitivity of flyhead and thorax acetylcholinesterase to leptophos-oxonin vitro, and tolerance to leptophos by the resistant strain is explained in terms of decreased rates of penetration and minor differences in metabolism.

Absorption and metabolism of a selective insecticide, 2,2-dimethyl-2,3-dihydrobenzofuranyl-7N-dimethoxyphosphinothioyl-N-Methylcarbamate, in bean plants

The absorption and metabolism of 2,2-dimethyl-2,3-dihydrobenzofuranyl-7N-dimethoxyphosphinothioyl-N-methylcarbamate (PSC), a selective, insecticidally active carbofuran derivative, was studied in red kidney bean plants. PSC was absorbed from hydroponic culture media and was translocated throughout the plants. PSC was metabolized to carbofuran, 3-hydroxycarbofuran, and 3-ketocarbofuran and these materials accounted for 25% of the recovered radioactivity. Each of these compounds are more toxic to mice than the parent compound. Additionally at least four other oxidized, hydroxylated and/or hydrolyzed metabolites were formed.