Comparative inhibition of aliesterases and cholinesterase in rats fed eighteen organophosphorus insecticides

Eighteen organophosphorus insecticides were fed to 30-day-old female rats for 1 wk at various dietary levels. Measurements were made of the inhibitory effects of the insecticides on aliesterases of serum and liver using diethylsuccinate and tributyrin as substrates. The cholinesterase activity of liver, serum, and brains of rats that received the same levels of the insecticides was also measured. Dose-related decreases in aliesterase activity were obtained with the appropriate dietary levels of each compound. The aliesterase activity of liver was more sensitive to inhibition than serum. The hydrolysis of tributyrin was inhibited at lower dietary levels than the hydrolysis of diethylsuccinate by liver, but hydrolysis of the two substrates by serum was affected to essentially the same extent. In most cases the dietary levels required to inhibit cholinesterase were considerably higher than the levels that inhibited aliesterases. When the aliesterase activity was depressed by feeding various levels of organophosphorus insecticides for 1 wk, the amount of potentiation of the toxicity of malathion was closely related to the amount of inhibition of liver aliesterases regardless of which compound was fed.