Larry G. Hart

Effects of Acute and Chronic DDT Administration on Hepatic Microsomal Drug Metabolism in the Rat.

Summary DDT, 500 ppm, was fed in a lab chow diet to rats. Hexobarbital sleeping times and in vitro assays were measured after 2 weeks, 1, 2, 3 and 4 months on the diet to observe the effects of DDT on hepatic microsomal drug metabolizing enzyme activity. With the exception of aniline, which was not different from control at 2 weeks, 3 and 4 months, significant increases in rate of drug enzyme activity were seen at all times on the diet for the drugs studied. Shortened sleeping times paralleled these increases. Acute treatment of rats with DDT at 3 dose levels, each for 3 days, produced significant stimulatory effects on drug metabolism in vitro at both 1 and 8 days. Sleeping times were depressed at both times, although this depression was significant only at 1 day. In mice, acute injection of a single dose of DDT did not shorten hexobarbital sleeping times even at 3 days after treatment. Several of the organophosphorous insecticides were screened acutely with sleeping times in mice and produced either no effects or in several cases a prolongation of sleeping times. The proposal was made that the stimulatory effects of DDT on enzyme activity were due to its causing a proliferation of smooth surfaced endoplasmic reticulum in the liver cell, with a consequent increase in the amount of the drug metabolizing enzymes.

Stimulatory effects of chlordane on hepatic microsomal drug metabolism in the rat

Abstract Technical chlordane, a halogenated hydrocarbon insecticide, and one of its pure isomers, γ-chlordane, were shown to have stimulatory effects on hepatic microsomal enzyme activity for the metabolism of certain drugs. Adult and weanling rats were injected intraperitoneally with both a single dose and three consecutive daily doses of chlordane at dose levels of 10, 25, and 100 mg/kg. Drug enzyme activity was determined on livers from these rats at 1, 8, 15, 22, and 29 days after the last injection. dl -Ethionine inhibited the increases in enzyme activity, keeping this activity at control levels. It was postulated that the latent and prolonged stimulatory effects of chlordane or its metabolites were due to its storage in body fat and subsequent gradual release. Chlordane is stimulatory to drug enzyme activity only when administered to the animal. Addition of chlordane to liver homogenates or particulate fractions incubated in vitro does not affect drug enzyme activity.

Further studies on the stimulation of hepatic microsomal drug metabolizing enzymes by DDT and its analogs

SummaryDDT is a long-lasting stimulator of drug metabolism in rats. This persistence of effect may be related to the long-lasting storage of DDT in body fat. Starvation of rats previously exposed to DDT can re-induce activation of hepatic drug metabolism, apparently by mobilizing DDT from body fat. Stimulation of hepatic drug metabolism can be demonstrated in rats maintained on diets containing as little as 5 ppm of DDT.All analogs and metabolites of DDT which were tested were active as stimulators of hepatic drug metabolism in the rat. However, only DDE was equipotent as a stimulator. Metabolism of DDT beyond DDE may reduce the ability of the molecule to function as an activator of hepatic microsomal enzymes.There may be a species difference in response of hepatic enzymes to DDT or its metabolites. A stimulation of hepatic drug metabolism by DDT or its analogs given as a single or repeated (daily for 3 days) injection could not be clearly demonstrated in mice. DDT and its analogs are the only insecticides tested which show this specific difference-chlordane and related structures markedly stimulate drug metabolism in both rats and mice.

Studies of the possible mechanisms by which chlordane stimulates hepatic microsomal drug metabolism in the rat

Abstract Chlordane has been compared with phenobarbital in its stimulatory action on hepatic microsomal drug metabolism in the rat. Both agents cause increases in liver weight, microsomal protein, microsomal NADPH oxidase, and microsomal cytochrome CO-binding pigment. Both agents can effect stimulation of drug metabolism in adrenalectomized or hypophysectomized rats, and ethionine can block the enzyme stimulation by both agents in normal rats. The stimulatory actions of chlordane on microsomal drug metabolism do not add to those by phenobarbital. The actions of both chlordane and phenobarbital seems to be associated with a proliferation of smooth endoplasmic reticulum in the liver cell. Both agents appear to affect very similar mechanisms in inducing increases in enzyme activity.

Studies using Clostridium botulinum toxin—Type A

Abstract Several drugs and ions were given to white mice injected with Clostridium botulinum type A toxin in an attempt to prolong survival time in these mice. Agents used included choline, barbital, chlorpromazine, Thio-TEPA, CaCl 2 , and MgCl 2 . Only choline had a significant effect, and its effect was to shorten survival time. Various tissues from rabbits intoxicated with either 2.0 ml or 4.0 ml of toxin were bioassayed for their ACh levels. The ACh content of diaphragm and iris-ciliary bodies from rabbits intoxicated with the higher dose appeared to be greater than control levels, as did the ACh level in brain from an animal severely intoxicated with the lower dose. Fetuses, livers, and brains from severely intoxicated pregnant rats were fed to fasted mice, and significant lethality was observed in mice after ingestion of fetuses or brain. This was felt to be suggestive evidence that the toxin may cross the placental “barrier”, and also the blood-brain “barrier”.

Influence of Hemicholinium No. 3 on Mammalian Tissue Levels of Acetylcholine.

Summary Hemicholinium No. 3 (HC-3) was administered acutely to cats, either as a 1% solution topically to the eyes or an i.v. injection of 1 mg/kg, and tissue levels of acetylcholine (ACh) were determined. The effects of nerve stimulation on ACh levels were also studied in these tissues, which included auricles, intestines and gastrocnemius muscles. Levels of ACh were significantly greater in control resting irises and ciliary bodies than in those treated with HC-3. The content of the auricles were also greater in the controls but only if nerve stimulation had been previously applied. Otherwise there were no differences between tissues from HC-3 treated and control animals. Another group of cats received a more chronic treatment with HC-3, 1 mg/kg repeated i.m. every 6 hours for a 24-hour period. Analysis of the same tissues for resting ACh content revealed no differences between treated and control animals. The results were discussed with regard to HC-3 exerting a possible anti-release mechanism. The possibility was also considered that much of the ACh might be of extraneural origin and not affected by HC-3.