Florence K. Kinoshita

Quantitative measurement of induction of hepatic microsomal enzymes by various dietary levels of DDT and toxaphene in rats

Abstract A study was conducted to develop procedures suitable for quantitative measurement of induction of hepatic microsomal enzyme activity by chemical agents fed in the diet of rats. The enzyme systems that catalyze the detoxification of EPN, the O-demethylation of p-nitroanisole, the N-demethylation of aminopyrine, and the reduction of p-nitrobenzoic acid were found suitable for this purpose. The activity of these enzymes can be measured quantitatively using whole-liver homogenates. Enzyme induction by DDT and toxaphene was studied by feeding various levels from 0.2 ppm to 50 ppm in the diet for periods up to 13 weeks. Induction of all the enzymes except reductase was produced by some dietary levels of both compounds. The lowest levels that produced a significant increase in any enzyme system were 1 ppm of DDT and 5 ppm of toxaphene. Maximal induction occurred within the first 3 weeks of the feeding period at all levels of each compound that caused enzyme induction; after this time the activity was maintained at a constant, elevated level until feeding of the pesticides was discontinued. The enzyme induction was more pronounced and occurred more rapidly in male rats than in females.

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

Abstract 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.

Influence of Induction of Hepatic Microsomal Enzymes by Phenobarbital on Toxicity of Organic Phosphate Insecticides

Summary A comparison was made of the toxicity of 15 cholinergic organic phosphates to normal rats and mice and to animals pretreated with phenobarbital for 5 days. The purpose of the study was to determine whether the hepatic microsomal enzyme induction caused by phenobarbital changed the acute toxicity of the organic phosphates. The study demonstrated that phenobarbital treatment either decreased the toxicity or had no effect on the toxicity of any of the compounds in either species with one exception being an increased toxicity of OMPA to phenobarbitaltreated rats.

Quantitative measurement of inhibition of aliesterases, acylamidase, and cholinesterase by EPN and Delnav®

Abstract A study was conducted in rats to develop procedures suitable for quantitative measurement of inhibition of aliesterases by organic phosphate insecticides. A suitable manometric procedure using diethylsuccinate and tributyrin as substrates was developed for this purpose. Acylamidase was measured by a previously developed method with acetanilid as the substrate. The applicability of these procedures for measuring aliesterase inhibition was demonstrated by feeding dietary levels of 0, 0.2, 1, 5, and 25 ppm of EPN and Delnav for 13 weeks. Aliesterase enzyme assays were performed on liver and serum by sacrificing animals at intervals during the feeding period, and cholinesterase activity was measured on these tissues and on brain. Maximal inhibition of aliesterase activity occurred early in the feeding period, and a dose-related response was obtained with both compounds. Aliesterases were much more sensitive to inhibition by EPN and Delnav than cholinesterase.

Induction of hepatic microsomal enzymes by herban, diuron, and other substituted urea herbicides.

Abstract 1-[5-(3a,4,5,6,7,7a-hexahydro-4,7-methanoindanyl)]-3,3-dimethylurea (Herban ® ) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) were administered to adult female rats to determine their enzyme-inducing capacity. After determining that these compounds have the ability to increase the activity of hepatic microsomal enzymes, they were fed to male and female weanling rats in the diet at levels of 100, 250, 500, 1000, and 2000 ppm. Dose-related increases in the activities of three hepatic microsomal enzymes were observed with maximal induction occurring during the first 3 weeks of feeding. All induced enzyme activities decreased during the duration of the 13-week study except for O -demethylase activity. A sex difference was observed in the response of the animals. Males were more susceptible than female rats to the enzyme-inducing activity of these two compounds. Other urea compounds were fed to weanling and adult female rats for 1 week at a dietary level of 1000 ppm. It was found that all the herbicidal urea derivatives that were used caused induction of at least one enzyme system.

Acute toxicity and anticholinesterase action of O,O-dimethyl O-[4-(methylthio)-m-tolyl] phosphorothioate (DMTP; Baytex) and related compounds☆

Abstract The acute toxicity of O,O -dimethyl O -[4-(methylthio)- m -tolyl] phosphorothioate (DMTP; Baytex; Bayer 29493) was studied. By the intraperitoneal route the LD 50 values ranged from 125 mg/kg to 325 mg/kg for mice, guinea pigs, and rats. By the oral route the LD 50 values ranged from 190 mg/kg to 310 mg/kg. The sulfoxide and sulfone derivatives of DMTP exhibited toxicity similar to that of the parent compound. Measurements of the anticholinesterase action of DMTP in vivo demonstrated that the enzyme activity of the brain and peripheral tissues exhibit similar susceptibility and the inhibitory effect is of long duration. The oxygen analog of DMTP was about 13 times more toxic than the parent compound by the intraperitoneal route to rats. The sulfoxide derivative of the oxygen analog was equal to the oxygen analog in toxicity, but the sulfone derivative was about 3 times more toxic than the oxygen analog. These possible metabolites of DMTP exerted a strong anticholinesterase action in vitro and the effects in vivo were much more rapidly reversible than those of DMTP. The S-methyl isomer was about 6 times more toxic than DMTP and differed in its in vivo anticholinesterase action by inhibiting the cholinesterase activity of the brain to a much lesser extent than peripheral tissues. Repeated daily injection of DMTP demonstrated that it has a marked tendency to produce cumulative toxic effects leading to mortality. Potentiation of acute toxicity was observed in rats when DMTP was given simultaneously with Delnav, Co-Ral, or malathion.

Stimulation of Detoxification of O-Ethyl O-(4-Nitrophenyl) Phenylphosphonothioate (EPN) by Nikethamide and Phenobarbital.

Summary Administration of nikethamide or phenobarbital to rats increases the rate of degradation of the organophosphorus insecticide, EPN, by a microsomal oxidase system in the liver. Induction of the activity of this system by nikethamide provides a possible explanation for the previously demonstrated ability of this drug to decrease the susceptibility of animals to the acute toxicity of EPN. In the present study there was good correlation between the extent of increase in activity of the detoxification enzyme system by nikethamide and phenobarbital and the ability of these compounds to reduce the acute toxicity of EPN to rats with phenobarbital being superior to nikethamide in both respects. It appears that the microsomal enzyme system that catalyzes the degradation of EPN to p-nitrophenol provides a practical means of testing various chemical agents for ability to induce synthesis of microsomal enzyme activity.

Acute toxicity and antiesterase action of O-ethyl-S,S-diphenyl phosphorodithioate (Hinosan®)

Abstract The acute toxicity of O-ethyl-S,S-diphenyl phosphorodithioate (Hinosan: Bay 78418) was studied in rats. By the ip route LD50 values were 25.5 ± 0.8 mg/kg and 66.5 ± 7.7 for adult female and male rats, respectively. An age difference in the susceptibility of male rats to the toxicity of Hinosan was noted, with young rats being more susceptible than adults. Hinosan was found to be an effective inhibitor of cholinesterase activity in vitro as evidenced by 50% inhibition of rat brain cholinesterase activity at a concentration of 1.05 × 10−6 m . Measurements of the anticholinesterase action of Hinosan in vivo demonstrated that the cholinesterase activity of the central and peripheral tissues was inhibited to an equal extent, and the inhibitory effect was rapid in onset and of long duration. Data obtained by feeding various levels of Hinosan showed that it is a potent aliesterase inhibitor. The toxicity of malathion to rats was markedly enhanced by prior administration. Pretreatment of rats with phenobarbital, DDT, 3-methylcholanthrene or testosterone markedly reduced the anticholinesterase action of Hinosan, suggesting that it is detoxified by an oxidative microsomal enzyme system.

Acute toxicity and anticholinesterase action of o,o-diethyl o-p-(methylsulfinyl)phenyl phosphorothioate (dmsp) and some related compounds

The acute toxicity of O,O-diethyl O-p-(methylsulfinyl)phenyl phosphorothioate (DSMP; Bayer 25141) was measured. By the intraperitoneal route the LD50 values ranged from 1.5 mg/kg to 10.5 mg/kg for rats, guinea pigs, and mice. When given orally the LD50 values were 2.2 mg/kg for female rats, 10.5 mg/kg for male rats, and 9 mg/kg for male guinea pigs. The sulfone derivative of DMSP exhibited toxicity similar to that of DMSP and the sulfide derivative was somewhat less toxic. The oxygen analogs of the phosphorothioates were all more toxic than the corresponding parent compounds. All the compounds included in this study exerted a strong anticholinesterase action in vivo. Maximum inhibition of the enzyme activity occurred in about an hour and the activity returned to nearly normal in about 5 days when equivalent fractions of the LD50 (58) were given.

Toxicity and enzyme-inducing activity of 4-fluoro-4′-trifluoromethyl benzophenone guanylhydrazone hydrochloride (FTBG)☆☆☆

Abstract The acute toxicity of a candidate antimalarial drug, 4-fluoro-4′-trifluoromethyl benzophenone guanylhydrazone hydrochloride (FTBG; WR 09792), was measured by intraperitoneal and oral administration to mice, rats, and guinea pigs. The LD50 values were between 11.5 and 27.9 mg/kg by the intraperitoneal route and between 114 and 199 mg/kg by the oral route. Subacute oral toxicity measurements demonstrated that a daily dose of 5 mg/kg was the highest dose that could be tolerated for 14 days without mortality or a decrease in leukocytes. Measurements of the effects of FTBG on hepatic microsomal enzymes demonstrated that this compound produces a marked and specific increase in the O-demethylase activity of the livers of rats when repeated daily doses are given intraperitoneally or orally. No induction of the other microsomal enzymes that were measured was noted, and induction of O-demethylase did not occur in mice and guinea pigs. Reversible, dose-related increases in O-demethylase activity occurred with 1 mg/kg and higher doses of FTBG daily for 5 days. Examination of structurally related compounds indicated that the trifluoromethyl substituent of FTBG is involved in the induction of O-demethylase activity.