Hepatic Microsomal Drug-metabolizing Activity Research Articles

Strain independent elevation of hepatic mono-oxygenase enzymes in female mice.

1. Hepatic microsomal drug metabolizing activity was compared in male and female AL/N, Balb/c, Balb/cJ, CD-1, C57BL/6J, C57BL/10J, DBA/2, and DBA/2J mice. 2. Cytochrome P-450-dependent hexobarbital hydroxylase and aminopyrine N-demethylase activities were sexually dimorphic with apparent maximal velocities consistently higher in females. Hexobarbital-induced sleeping times were greater in males, corresponding to their lower hepatic mono-oxygenase enzyme activities measured in vitro. 3. No murine sex differences were observed for the hydroxylation of aniline, while UDP-glucuronyltransferase activity was strain dependent with either no sexual dimorphism or higher activities in males. 4. Testectomy resulted in an elevation of hepatic hexobarbital metabolism to female levels in all strains examined. Thus, decreased hepatic cytochrome P-450-dependent xenobiotic metabolism in adult male mice results from the suppressive effects of gonadal androgens. 5. Sexually dimorphic patterns of hepatic hexobarbital and aminopyrine metabolism in adult mice are opposite in orientation and lower in magnitude than the well established relationship in rats in which these same substrates are metabolized at a rate 3 to 5 fold higher in intact males as compared to females or gonadectomized males.

Studies on the effect of chronic consumption of moderate amounts of ethanol on male rat hepatic microsomal drug-metabolizing activity

Weanling, male Sprague-Dawley rats given 10% ethanol in the drinking water and food ad lib. for up to 8 weeks consumed 17% of their calories as ethanol. The alanine aminotransferase (ALT), aspartate aminotransferase (AST), and liver histology by light microscopy were unaffected by this treatment. Similarly, hepatic microsomal NADPH-cytochrome c reductase, ethylmorphine N-demethylase and benzphetamine N-demethylase activities were also not affected by ethanol consumption. On the other hand, cytochrome P-450 content, aniline hydroxylase activity and acetaminophen metabolism as measured by both the cysteine conjugate and the [ 3H]acetaminophen covalently-bound to microsomal protein were increased significantly by ethanol consumption. The maximal effect was seen by 6 weeks. The 2- to 3-fold increase in aniline and acetaminophen metabolism, the absence of liver damage, and the similarity in weight gains and caloric intakes for controls and treated animals suggest that the rat on 10% ethanol in the drinking water is a reasonable model for studies of the effect of moderate alcohol consumption on specific biochemical pathways.

Induction of tolerance in mice and rats to the effect of endotoxin to decrease the hepatic microsomal mixed-function oxidase system. Evidence for a possible macrophage-derived factor in the endotoxin effect

Daily administration of low, non-lethal doses of bacterial endotoxin to mice and rats has been shown to induce tolerance to the effect of an acute challenge dose of endotoxin to decrease the hepatic microsomal drug metabolizing activity, the level of cytochrome P-450, and to increase heme oxygenase activity. The serum collected at various times after injection of endotoxin into control animals when injected into untreated animals markedly depressed aniline hydroxylase activity, ethylmorphine N-demethylase activity, and the level of cytochrome P-450. Tolerant animals were not affected by the post-endotoxin serum injection, suggesting the decreased activity caused by the serum in untreated animals was probably due to endotoxin contained in the serum. Injection of tolerant mice and rats with supernatant medium obtained from cultures of peritoneal macrophages incubated with 100 μg/ml of endotoxin caused a loss of hepatic microsomal drug-metabolizing activity, and a decrease in the level of cytochrome P-450. These results suggest that peritoneal macrophages release a factor in response to endotoxin that mediates the decreased hepatic mixed-function oxidase activity.

Endotoxin depression of hepatic mixed function oxidase system in C3H/HeJ and C3H/HeN mice

The effect of endotoxin to depress the hepatic drug-metabolizing enzyme activity has been studied in the C3H/HeJ and C3H/HeN strains of mice. The C3H/HeJ mouse strain is generally considered to be unresponsive to the biological effects of endotoxin. However, injection of these mice with 0.5 mg/kg body weight of E. coli endotoxin (Westphal extracted) produced a decrease in the rate of N-demethylation of ethylmorphine and in the levels of cytochrome P-450 and cytochrome b5 comparable to that observed in the endotoxin-sensitive C3H/HeN mouse strain. Although the mechanism of endotoxin action to decrease hepatic microsomal drug-metabolizing activity is presently unknown, the results suggest that: 1) the C3H/HeJ mouse strain is responsive to this endotoxin effect, and 2) that cellular constituents other than B-cells or macrophages are probably involved in eliciting the response, since these cells of the C3H/HeJ mouse are unresponsive to endotoxin.

Microsomal drug metabolism in acute and chronic galactosamine induced hepatic injuries.

To determine the microsomal functions of the injured liver, female rats were given D-galactosamine (GalN) acutely (400 mg/kg body weight, i.p.) or chronically (250 mg/kg body weight for 7 months, daily, i.p.). In the acute study, GalN administration resulted in a five-fold increase in hepatic triglyceride content. Microsomal protein and phospholipid concentrations were not affected. However microsomal cytochrome P450 content and aminopyrine demethylase and also aniline hydroxylase activities were significantly decreased whether expressed per mg of microsomal protein or per gram of liver. Cytochrome b5 content was significantly increased. By contrast, chronic administration of GalN produced a marked hepatomegaly and an extensive hepatic fibrosis with nodular formation without triglyceride accumulation. Electron-microscopically, there was apparent proliferation of mitochondria, and smooth endoplasmic reticulum showed focally accentuated hypertrophy without liposomes in the dilated tubules. Although microsomal protein concentration was significantly decreased, cytochrome P450 content was increased significantly when expressed per mg of microsomal protein or per unit of body weight. The aminopyrine demethylase activity was significantly enhanced only when expressed per unit of body weight. In both acute and chronic studies, microsomal glucose-6-phosphatase activity was significantly reduced. These data suggest that in acute liver injury, there is an impairment of hepatic microsomal drug metabolizing activity, whereas in chronic liver injury, there is an apparent enhancement of the activity possibly due to an enlarged hepatic mass even in the presence of a decreased drug metabolizing capacity per unit of the injured liver.

Effect of acetone administered in vivo upon hepatic microsomal drug metabolizing activity in the rat

The effects of acetone administered to female rats in vivo, upon the metabolism of drugs by the hepatic microsomal subcellular fraction have been studied. There is a rapid increase, maximal at 0·5 hr in aniline p-hydroxylation of 69 per cent, and an inhibition of aminopyrine N-demethylation of 61 per cent. Thereafter levels return to control values. There is a slower increase in aniline p-hydroxylation of 168 per cent, maximal at 48 hr. whilst aminopyrine N-demethylation is unaltered. Cycloheximide has no effect upon the changes in activity after 0·5 hr but blocks the increase in aniline p-hydroxylation 48 hr after the administration of acetone. It is suggested that acetone may contribute to the changes in drug metabolizing activity found in diabetic animals.

Effects on drug metabolism of carbaryl and 1-naphthol in the mouse

The effects of carbyl and 1-naphthol on hepatic microsomal drug-metabolizing enzyme systems were investigated. The agents were fed at a level of 25 mmol/kg of feed to groups of young male Swiss-Webster mice for 14-day periods. Body weight was depressed by carbaryl, but not by 1-naphthol. The rates of in vitro metabolism of aniline and benzphetamine were greater than control rates in livers of mice fed carbaryl, but the rate of in vivo hydrolysis of the carbamate insecticide Zectran was decreased by carbaryl feeding. Administration of 1-naphthol did not change the rates of in vitro metabolism of either aniline or benzphetamine. Hepatic microsomal concentrations of cytochromes P-450 and b 5 were increased by carbaryl, but feeding of 1-naphthol did not affect levels of either cytochrome. Radiolabeled pentobarbital disappeared from the blood of carbaryl-fed mice more rapidly than from the blood of control animals, and carbaryl-fed mice slept a shorter period of time than controls following pentobarbital administration. The LD50 of an acute oral dose of carbaryl was increased two-fold by feeding carbaryl for 14 days. It was concluded that carbaryl is a weak inducer of hepatic microsomal drug-metabolizing activity, and that the effects observed are not likely due to 1-naphthol.

Effect of acute alpha-naphthylisothiocyanate administration on hepatic microsomal drug metabolism in the mouse.

SummaryWhen alpha-naphthylisothiocyanate was administered orally to mice, the hepatic microsomal drug metabolizing activity for hexobarbital and aniline was significantly depressed 2 hours after treatment; the inhibition persisted for 9 days. Chlorpromazine metabolism was not affected. Phenylisothiocyanate and beta-naphthylisothiocyanate also inhibited some drug metabolizing pathways at 2 hours, but were neither as effective, nor as persistent, as alpha-naphthylisothiocyanate. Alpha-naphthylisothiocyanate and phenylisothiocyanate added directly to hepatic microsomes inhibited hexobarbital metabolism in concentrations as low as 10-5 M. Chlorpromazine metabolism was affected only when the concentrations were 10-3 M.