Chozo Mitoma

Nature of the effect of caffeine on the drug-metabolizing enzymes☆

Abstract Pretreatment of the rat for 3 days with caffeine resulted in an elevation in the drugmetabolizing activity by the hepatic microsomal system. This effect is counteracted by the simultaneous administration of actinomycin D. Caffeine also shortened the duration of action of zoxazolamine and methyprylon in the rat. The stimulatory effect of caffeine on drug metabolism was additive to that of phenobarbital when acetanilide was the substrate but not when o -nitroanisole or aminopyrine was used. Attempts to show increased amino acid incorporation or an increase in cytochrome P-450 in the microsome were not successful. An interesting feature of the stimulatory effect of caffeine on drug metabolism is its short duration after the termination of treatment. Phenobarbital was used throughout this study as a reference compound.

Metabolic studies of tolbutamide in the rat

Abstract Hydroxymethyltolbutamide was found to be the major oxidation product in the urine of rat and rabbit given tolbutamide. The metabolite was identified by its infrared spectrum and by paper and thin-layer chromatography. The enzyme system responsible for the oxidation of tolbutamide is a typical microsomal drug-metabolizing system subject to induction by 3,4-benzpyrene, phenobarbital, and tolbutamide itself. The only product observed after incubating tolbutamide with either the fortified microsomes or with liver homogenate was hydroxymethyltolbutamide. Only a small isotope effect was seen in the oxidation of trideuterated tolbutamide. Hydroxymethyltolbutamide was approximately half as active as tolbutamide in its hypoglycemic activity in mice.

Metabolic Disposition Study of Chlorinated Hydrocarbons in Rats and Mice

Chlorinated hydrocarbons found in a bioassay to be carcinogenic to both B6C3F1 mice and Osborne-Mendel rats (1,2-dichloroethane), carcinogenic only to mice (1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane, hexachloroethane, trichloroethylene, and tetrachloroethylene), and noncarcinogenic to either species (1,1-dichloroethane and 1,1,1-trichloroethane) were used to investigate the biochemical bases for tumorigenesis. Studies were conducted after chronic oral dosing of adult mice and rats with the MTD and 1/4 MTD of each compound. The extent to which the compounds were metabolized in 48 hr, hepatic protein binding, and urinary metabolite patterns were examined. Metabolism of the compounds (mmoles per kg body weight) was 1.7 to 10 times greater in mice than in rats. Hepatic protein binding (nanomole equivalents bound to 1 mg of liver protein) was 1.2 to 8.3 times higher in mice than in rats except for 1,2-dichloroethane and 1,1,1-trichloroethane. The noncarcinogens 1,1-dichloroethane and 1,1,1-trichloroethane exhibited 2 to 18 times more binding in mice than did the carcinogens 1,2-dichloroethane and 1,1,2-trichloroethane. Urinary metabolite patterns of the compounds were similar in both species. The biochemical parameters measured provided no clue to differentiate the carcinogens from the noncarcinogens.

Effects of various chemical agents on drug metabolism and cholesterol biosynthesis

Abstract The effects of representative inhibitors of drug metabolism, hypocholesterolemic agents and insecticide synergists on microsome-catalyzed drug metabolism and cholesterol biosynthesis were examined in the rat. In the experiments in vitro , both biochemical reactions were inhibited to varying degrees by all of the test compounds. Cholesterol biosynthesis appeared to be more sensitive to these compounds than was the drug metabolism system. However, in an experiment in vivo , only microsome inhibitors prolonged the sleeping time of mice induced by hexobarbital. The administration of AY-9944 and Compound A at doses sufficient to lower the plasma cholesterol level had no effect on the microsomal enzyme activity. Two effects on cholesterol metabolism were observed with microsome inducers. Administration of 3,4-benzpyrene resulted in an elevated plasma cholesterol level in the rat. However, the incorporation of 14 C-labeled acetate or mevalonic acid into cholesterol by the liver of benzpyrene-treated rats was not higher than that by the liver of the control rats. Phenobarbital did not elevate the plasma cholesterol level, but the liver from phenobarbital-treated rats showed increased 14 C-acetate incorporation into cholesterol.

Effect of caffeine on hepatic microsomal cytochrome P-450

Abstract Previously we reported that pretreatment of rats with caffeine did not result in any observable increase in the P-450 hemoprotein content of the liver microsomes. However, the measurement of ethyl isocyanide difference spectra of dithionite reduced microsomes showed a small but definite increase in the 455-nm peak in the caffeinetreated group. There was no significant increase in the 430-nm peak. In this respect, caffeine action resembled that of 3-methylcholanthrene. Caffeine treatment also increased the rate of NADPH-cytochrome P-450 reductase activity. Microsomal enyzme induction by caffeine was not obliterated by adrenalectomy. The preferential increase in the 455-nm peak was more pronounced in the microsomes of the adrenalectomized animal after caffeine pretreatment.

Evaluation of hepatocytes isolated by a nonperfusion technique in a prescreen for cytotoxicity

Twenty-three chemicals, differing widely in cytotoxic (hepatotoxic) potency in vivo, were examined to determine their ability to release glutamic-oxaloacetic transaminase (GOT) from hepatocytes isolated by a nonperfusion method from rat liver. The test chemicals were carbon tetrachloride, chloroform, 1,1,2- and 1,1,1-trichloroethane, six bromobenzene analogs, tri-n-butyl tin, chlorpromazine, tetracycline, halothane, phenobarbital, L-ethionine, acetaminophen, thioacetamide, allyl alcohol, ethanol, ascorbic acid, dimethyl sulfoxide, and acetone. In all but two cases--thioacetamide and allyl alcohol--there was a good correspondence between chemicals active in the assay as now performed and those that elevate serum transaminase and cause liver injury on short-term exposure in vivo. These results indicate that with further effort it may be possible to develop an effective, inexpensive, and rapid prescreen to identify drugs and environmental chemicals that are potentially cytotoxic to animals and humans.

Influence of fasting on the absorption and effects of δ9-tetrahydrocannabinol after oral administration in sesame oil

Tissue levels of 3H were higher 2 hr after oral administration of 3H-delta9-THC (10 mg/kg in sesame oil) to male Fischer rats in the morning compared with treatment in the afternoon. A corresponding reduction in potency was seen for the impairing effect of delta9-THC on performance of a conditioned avoidance response (CAR). The hypothesis that these effects were related to the interval between feeding (which normally occurs during the night in the nocturnal rat) and drug administration was supported when they were mimicked in overnight fasted and ad lib fed rats. Food deprivation decreased the rate of gastrointestinal absorption of 14C-delta9-THC in sesame oil. Peak plasma levels of 14C occurred 2-4 hr after administration in fed rats compared with 8 hr in fasted rats. When tested 2 hr after oral administration, delta9-THC caused significantly greater impairment of CAR performance in fed than fasted rats, whereas the opposite was found after 8 hr. Extraction and subsequent thin layer chromatography of plasma and brain from fed and fasted rats sacrificed 2 or 8 hr after oral administration of 10 mg/kg 14C-delta9-THC showed that brain levels of 11-hydroxy-delta9-THC rather than delta9-THC were correlated with the behavioral effect.

Metabolic Studies on Trimethoxyamphetamines

Summary TMA-2 is a more potent psychotomimetic agent than TMA-3 but the latter is taken up by the rat brain to a greater extent than the former. These compounds are demethylated by the liver microsomal enzyme that does not respond to phenobarbital induction.

The relative effectiveness of several hallucinogens in disrupting maze performance by rats

SummaryThe effects of hallucinogens and their nonhallucinogenic analogs on the performance of rats on the Lashley-III underwater maze were evaluated. After the rats were trained to swim through the maze without an error, they were injected i.p. with test compounds or saline solution and tested at various intervals after the injection. A substantial number of the treated animals made one or more errors. The time of peak effect of lysergic acid diethylamide (LSD-25) and mescaline was 15 min after the injection; that of 2-brom-lysergic acid diethylamide (BOL-148) and of several trimethoxyamphetamines (TMA) was 30 min; and that of d-amphetamine was 45 min. The dose-response curves showed that the effect of the compounds was a function of dose. The median effective doses (ED 50) in μmol/kg were: LSD-25 (0.3); TMA-2 (12.8); BOL-148 (15.9); d-amphetamine (32.0); TMA (33.4); TMA-6 (46.0); TMA-3 (52.1); mescaline (91.0); and TMA-4 (94.0). The rank order of potency of the compounds is, in general, similar to that derived from the data on man.

Transport and Incorporation of Labeled Compounds in Experimental Phenylketonuric Rats

Summary In hyperphenylalaninemia induced by daily injections of phenylalanine to growing rats, the entry of α-methyl-D-glucose or glucose into the brain is not hindered. Thus, defective utilization of glucose due to high levels of phenylalanine and its metabolites appears to be the reason for its reduced incorporation into lipids and proteins. On the other hand, decreased incorporation into proteins of amino acids such as glutamic acid and leucine appears to be due to the poor uptake by the brain of these amino acids.