Differential action of progesterones on hepatic microsomal activities in the rat.

A significant reduction was found in the activity of drug-metabolizing enzymes (aminopyrine N-demethylase and coumarin 3-hydroxylase) and glucose 6-phosphatase in hepatic microsomes after the administration of reduced derivatives of progesterone (5α-pregnane-3β,-ol-20-one, 5β-pregnane-3α-ol-20-one, 5α-pregnane-3β,20β-diol and 5β-pregnane-3α,20α-diol) to rats. These steroids slightly raised inosine diphosphatase activity. On the other hand, 16α-hydroxyprogesterone and pregnenolone-16α-carbonitrile significantly increased drug metabolism and slightly elevated glucose 6-phosphatase. The contrasting action of the different progesterone derivatives was associated with changes in microsomal phospholipid synthesis. Pregnanolone and pregnanediol significantly decreased the de novo incorporation of [¹⁴C-Me]-l-methionine into microsomal phospholipids, mainly manifesting in phosphatidylcholine, phosphatidylethanolamine and lysophosphatidylcholine fractions; reduced the activity of S-adenosyl-l-methionine:microsomal-phosphatidylethanolamine methyl transferase; and caused a reduction of total microsomal phosphatidylcholine:phosphatidylethanolamine ratio. In contrast, 16α-hydroxy-progesterone and pregnenolone-16α-carbonitrile increased the de novo synthesis of microsomal phospholipids, methyl transferase activity and the ratio of total microsomal phosphatidylcholine: phosphatidylethanolamine. Treatment of rats with reduced progesterone derivatives diminished microsomal progesterone hydroxylation in the 16α- and 6β-position and raised progesterone Δ⁴-5α-dehydrogenase activity measured in vitro. On the other hand, 16α-hydroxyprogesterone and pregnenolone-16α-carbonitrile elevated progesterone hydroxylation. Considering these opposite effects it can be postulated that in the rat the induction of drug-metabolizing activity of the hepatic endoplasmic reticulum might be controlled by a balance displayed in the synthesis and metabolism of various progesterone derivatives.     

Hormonal regulation of drug metabolism during pregnancy.

During pregnancy, a significant change has been found in the pattern of liver response to drugs. The activity of drug-metabolizing enzymes was inhibited due to the presence of increased amounts of reduced progesterone metabolites produced by the pregnant animal. Treatment of non-pregnant rats with 5alpha-pregnan-3beta-ol-20-one or 5alpha-pregnan-3beta,20beta-diol also caused a decreased drug hydroxylation. On the other hand, the administration of 16alpha-hydroxyprogesterone resulted in an increased activity. The contrasting effects of the different steroids on the function of the endoplasmic reticulum have shown correlation with changes in microsomal phospholipid synthesis. Reduced progesterone derivatives brought about a decrease, whereas hydroxyprogesterone an enhancement. The opposite actions provided evidence to postulate that during pregnancy the formation of endoplasmic reticulum and associated induction processes of drug metabolism might be regulated by a balance displayed in the production of various progesterone metabolites.     

Effect of pregnancy on hepatic microsomal drug metabolism in rabbits and rats

In Dutch-belted rabbits, pregnancy caused several-fold decrease of in vitro hepatic microsomal aminopyrine, benzphetamine, and hexobarbital biotransformations. In pregnant Sprague-Dawley rats, various kinds of expressing the in vitro rates of hexobarbital biotransformation (per mg of microsomal protein, g of liver, 100 g of body weight) indicated unchanged or slightly elevated microsomal enzyme activity. In vivo, the course of hexobarbital blood levels after i. p. hexobarbital sodium, 100 mg/kg, indicated that the fate of hexobarbital was not primarily determined by the small changes of microsomal enzyme activity but, rather, by changed hexobarbital distribution. Different ways of expressing in vitro rates of aniline biotransformation showed decreased or unchanged enzyme activity during pregnancy and in vivo experiments indicated that these changes did not affect aniline metabolism in living rats. The results pointed out marked species differences in the effect of pregnancy on drug metabolism. Interpretation of in vitro biotransformation data for living animals suggested that with different substrates, microsomal enzyme activity and distribution, respectively, may exert different effects playing either significant or apparently minor role in drug disposition.Supported in part by U.S. Public Health Grant NIGMS 12,675.     

Effect of polychlorinated biphenyls (PCBs) administration on phospholipid biosynthesis in rat liver

The effect of PCBs or phenobarbital on the biosynthesis of phospholipids in hepatic endoplasmic reticulum of rats was studied by the intraperitoneal injection of [³²P]orthophosphate, [Me?¹⁴ C]choline or [2?³H]glycerol. Significant increases in liver microsomal phospholipid content after the administration of either PCBs or phenobarbital indicated the actual proliferation of endoplasmic reticulum membranes. The rate of both [³²P] and [¹⁴C] incorporations into microsomal choline-containing phospholipids, such as phosphatidylcholine, sphingomyelin and lysophosphatidylcholine, was reduced to one fifth by PCBs administration compared with control animals. The incorporation of [³²P]orthophosphate into phosphatidylethanolamine or other phospholipid classes was less or not affected, respectively, by PCBs administration. The specific inhibitory effect of PCBs on the incorporation into cholinecontaining phospholipids was not observed when [2?³-H]glycerol was used as a precursor. Phenobarbital administration, however, increased significantly the rate of [³²P] incorporation into liver phospholipids, especially phosphatidylcholine. It is suggested that the increase in microsomal phospholipid content by PCBs administration is not due to the stimulation of synthesis but to the inhibition of the catabolism of membrane phospholipids and that the increase in content caused by phenobarbital is due at least in part, to the stimulation of synthesis. The possible site(s) of PCBs-induced inhibition of phospholipid biosynthesis in rat liver is discussed.     

Effect of phenobarbital on methyl transfer between methylated drugs and hepatic microsomal phospholipids.

The effect of phenobarbital on the incorporation of the label from N-[¹⁴C-Me]nicotine and [¹⁴C]formaldehyde into hepatic phospholipids of the rat has been studied. ¹⁴C was utilized for the formation of methylated phospholipids from both precursors. Phenobarbital elicited no significant action either on the synthesis of total hepatic phospholipids or on the incorporation of radioactivity into the total or individual liver phospholipid fractions. However, this treatment increased phospholipid content and the uptake of the label from nicotine into microsomal phospholipids. Phenobarbital raised microsomal phosphatidylethanolamine, -choline (PC), -serine (PS), and lysophosphatidylcholine contents and the incorporation of ¹⁴C-labeled methyl groups from nicotine into PC and PS fractions. Radioactivity from [¹⁴C]formaldehyde was also incorporated into hepatic phospholipids. Phenobarbital however, had no significant effect on the incorporation either into total or microsomal phospholipids. Comparing the utilization of ¹⁴C for synthesis of liver microsomal phospholipids from N-[¹⁴C-Me]nicotine or [¹⁴C]formaldehyde with the natural methyl donor, l-[¹⁴C]-Me]methionine, greater amounts were taken up from methionine than nicotine or formaldehyde. The methyl group of nicotine was probably incorporated into phospholipids via the metabolic pool; the enhancing effect of phenobarbital on this process was associated with increased metabolism and with increased methyl transfer into methyl group containing microsomal phospholipids.     

Effects of pregnancy on the metabolism of drugs in the rat and rabbit

In rats 19–20 days pregnant, liver weight is increased by 40 per cent, cytochrome P-450 concentration is decreased by 25 per cent and the specific activities of 4-methylumbelliferone glucuronyl transferase and biphenyl-4-hydroxylase are reduced by 25 and 30 per cent, respectively; biphenyl-2-hydroxylase and p-nitrobenzoic acid reductase are not changed. In rats, 15–16 days pregnant, liver weight is increased by 33 per cent but the concentration of cytochrome P-450 and the specific activities of the drug microsomal enzymes are unchanged. Expressed as total amounts per whole liver, there is an increase in microsomal protein and nitro-reductase in both 15–16 and 19–20 day pregnant animals but no changes occur in cytochrome P-450, glucuronyl transferase or biphenyl hydroxylases.Hexobarbital administered to rats at doses related to pregnant body weight increases the sleeping-time from 50 min in non-pregnant animals to 110 min at full-term, but when administered on the basis of the non-pregnant body weight the duration of anaesthesia remains unchanged.Pretreatment of pregnant (19–20 days) and non-pregnant rats with phenobarbital leads to similar increases in microsomal protein (25 per cent) and nitroreductase activity (40 per cent); cytochrome P-450 is increased in non-pregnant animals (30 per cent) but not in the pregnant, although biphenyl-4-hydroxylase is increased in both to such extents as to annul the inhibitory effect of pregnancy. Pretreatment with methylcholanthrene gives rise to similar increases in cytochrome P-450 (30 per cent) and biphenyl-2-hydroxylase (10-fold increase) in both pregnant and non-pregnant rats and again increases biphenyl-4-hydroxylase so as to annul the effect of pregnancy.With rabbits, no change occurs in liver weight, microsomal protein, nitro-reductase, cytochrome P-450, or biphenyl-4-hydroxylase at full-term pregnancy, but glucuronyl transferase is reduced by 20 per cent, and coumarin-7-hydroxylase by 60 per cent. Pretreatment of rabbits with phenobarbital increases microsomal protein (15, 25 per cent), nitro-reductase (70, 80 per cent), cytochrome P-450 (130, 90 per cent), biphenyl-4- hydroxylase (50, 60 per cent), coumarin-7-hydroxylase (40, 150 per cent), and glucuronyl transferase (65, 15 per cent) in both non-pregnant and pregnant animals, respectively.The decrease during pregnancy of hepatic glucuronyl transferase is attributed to competitive inhibition by high levels of endogenous estrogenic and progestational steroids, but the decrease in the activities of the microsomal hydroxylating enzymes is attributed to the decrease in P-450, which may result from high levels of growth factors.     

Morphological and biochemical changes in the liver of various species in experimental phospholipidosis after diethylaminoethoxyhexestrol treatment.

The mechanism of druginduced experimental phospholipidosis was studied in several species by the administration of diethylaminoethoxyhexestrol. Rabbits, rats, mice, dogs, and guinea pigs developed microscopic and biochemical abnormalities, while hamsters were less affected. In the liver of affected species characteristic subcellular changes were found, accompanied by phospholipid accumulation. Hepatic lesions consisted of concentric lamellar bodies with varying degrees of osmic affinity, representing secondary lysosomes characterized by cytochemical methods. Accumulation of these bodies was also seen in Kupffer, endothelial, and biliary epithelial cells. The intensity of the changes was related to species susceptibility. Biochemical studies revealed an overall increase of total phospholipids in the affected species, together with changes in the relative distribution of individual phospholipids and the appearance of unidentified components. The activity of microsomal drug metabolizing enzymes and microsomal phospholipid synthesis were diminished. The lesions closely resembled those observed in man after treatment with diethylaminoethoxyhexestrol and are related to altered phospholipid metabolism with subsequent changes in microsomal drug metabolizing enzyme activity.     

Induction of hepatic mono-oxygenase systems of pregnant rats with phenobarbital and 3-methylcholanthrene.

When sodium phenobarbital was given to pregnant and non-pregnant female rats (40 mg/kg for 4 days), ethylmorphine N-demethylase, a cytochrome P-450-dependent system, was induced about 4-fold in non-pregnant females, but only 2-fold in pregnant females. The induction of microsomal cytochrome P-450 was also lower in pregnant animals. This impairment of phenobarbital induction occurred within 3 days of conception and disappeared after parturition within 5 days. 3-Methylcholan-threne induction of hepatic benzo[a]pyrene hydroxylase, a cytochrome P₁-450-dependent mono-oxy-genase system not inducible by phenobarbital, was not impaired during pregnancy. The depressed response of the maternal liver to phenobarbital induction can be partially reversed by the coadministra-tion of 3-methylcholanthrene. The administration of a higher dose of sodium phenobarbital (80 mg/kg day for 4 days) overcame the pregnancy-related lowered response to phenobarbital induction observed with the smaller dose of the barbiturate. The similarity in responses of the maternal and fetal livers to inducing agents suggests that a common regulatory mechanism operates in both the fetus and the pregnant female.     

Effects of a choline-deficient diet on the induction of drug- and ethanol-metabolizing enzymes and on the alteration of rates of ethanol degradation by ethanol and phenobarbital.

Phosphatidylcholine has been shown to be an essential component for electron transport to cytochrome P-450 and for hydroxylation of a number of substrates by microsomes in vitro. A choline-deficient diet was fed to rats for 3 weeks in order to study the effect in vivo of alterations of liver phospholipids on the activity of microsomal enzymes, on parameters of ethanol metabolism, and on the adaptive responses of both to ethanol and phenobarbital administration. Choline deficiency resulted in an increase in total liver lipids and triglycerides, but in a decrease in total phospholipids, due mostly to a decrease in phosphatidylcholine. Choline deficiency did not result in changes in microsomal enzymes or parameters of ethanol metabolism. However, it did prevent optimal induction of aniline hydroxylase activity and cytochrome P-450, by both ethanol and phenobarbital, and of microsomal protein concentration and cytochrome b₅ by phenobarbital; it also prevented ethanol-induced increases both in the activity of the microsomal ethanol-oxidizing system and in the rates of ethanol disappearance from the blood. Alcohol dehydrogenase activity remained unchanged. This study demonstrates that dietary choline is required for optimal induction of microsomal enzymes by both ethanol and phenobarbital, and for increases in ethanol metabolism induced by ethanol administration. It is suggested that a decrease in available hepatic phosphatidylcholine, due to choline deficiency, is a cause of inhibition of the optimal induction of microsomal enzymes.     

Comparison of gamma-glutamyl transferase induction by phenobarbital in the rat, guinea pig and rabbit

Serum and hepatic γ-glutamyl transferase (GGT) activities were correlated with the microsomal markers cytochrome P-450 and aminopyrine N-demethylase after i.p. injection of phenobarbital (PB) to rats, guinea pigs and rabbits. The response to PB in the regimen employed was greatest in the rabbit and least in the guinea pig. Great disparities were observed in the microsomal protein contents following PB administration to the three species, masking the responses of the other indices when these were related to protein contents rather than to tissue weights. The increased hepatic GGT activities in PB-treated guinea pigs and rabbits were reflected in increased serum activities of this enzyme; the hepatic and serum GGT activities showed an excellent correlation with cytochrome P-450 and aminopyrine N-demethylase activities, supporting the view that the changes in GGT activity were related to enzyme induction. Although hepatic GGT activity in PB-treated rats also showed good correlation with enzyme induction indices, activity of this enzyme in rat serum was undetectable in control and PB-treated animals. Analysis of ribosome-free microsomal proteins by sodium dodecylsulfate (SDS)-polyacrylamide gel electrophoresis confirmed the marked increase in three bands in the PB-treated rat, but quite different changes were noted in the guinea pig and the rabbit. Our results extend knowledge about the heterogeneous response to PB shown by different animal species. The data provide further evidence that GGT is a PB-inducible enzyme, and suggest that the rabbit is the best model for elucidating the relationship between enzyme induction and GGT activity occurring in several human clinical situations.     

Effect in rats of subacute administration of ethosuximide, methsuximide and phensuximide on hepatic microsomal enzymes and porphyrin turnover

Oral administration of the closely related antiepileptic succinimides, ethosuximide, methsuximide and phensuximide, to male rats daily for 3 days, increases the activity of the hepatic microsomal enzymes as judged in vivo by the reduction of hexobarbitone-induced hypnosis and in vitro by increased oxidation of hexobarbitone and hydroxylation of aniline. Increased liver/body weight, liver microsomal cytochrome P-450 and hepatic δ-aminolaevulinic acid synthetase and a proliferation of the hepatic smooth endoplasmic reticulum are associated with the increase in drug metabolism. Daily administration of methsuximide to rats for 3 days reduces the anticonvulsant activity of the drug presumably by increasing its metabolism. In the rat, the synthesis of porphyrins by the liver is not affected by the treatment with any of the succinimides. However, methsuximide and phensuximide, but not ethosuximide, exhibit marked porphyrogenic activity in chick embryo liver. Of the three drugs, only methsuximide interacted with rat liver microsomal cytochrome P-450 to produce a type I spectral shift. The significance of the results is discussed in relation to the clinical use of these antiepileptic drugs.     

Effects of dietary pectin and cellulose on hepatic and intestinal mixed-function oxidations and hepatic 3-hydroxy-3-methylglutaryl-coenzyme a reductase in the rat

The aim of this study was to determine if feeding dietary fiber (cellulose or pectin) to male rats could influence hepatic and intestinal mixed-function oxidation. We simultaneously compared hepatic drug-oxidizing activity with the activity of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, the rate-controlling enzyme for cholesterol biosynthesis. Three groups of six animals were fed a purified diet containing by weight either 10.4% cellulose or 10.4% pectin, or a standard cereal-based diet containing 4.5% crude fiber; the caloric contributions by carbohydrate, protein and fat in the three diets were similar. In the cellulose-fed rats, the hepatic microsomal cytochrome P-450 content and the activities of ethylmorphine N-demethylase and aniline hydroxylase were significantly lower when compared with those of rats fed pectin or the cereal-based diet. The hepatic microsomal cytochrome P-450 content and the activities of ethylmorphine N-demethylase and aniline hydroxylase were similar in the pectin-fed and cereal diet-fed rats. Hepatic HMG-CoA reductase activity, hepatic microsomal cytochrome b₅ content, and intestinal benzo[a]pyrene hydroxylase activity were comparably lower in rats fed the purified diet with either dietary fiber when compared to those fed the cereal diet. It is concluded that dietary pectin and cellulose exert distinctly different influences on the hepatic microsomal mixed-function oxidase system for drug metabolism, but not on liver cholesterol synthesis or intestinal benzo[a]pyrene hydroxylation, suggesting that different physiological mechanisms control these enzyme systems.     

Selenium antagonism of cadmium-induced inhibition of hepatic drug metabolism in the male rat

Experiments were undertaken to examine the effect of selenium, an essential trace element, on cadmium-induced inhibition of drug metabolism in male, Sprague-Dawley derived rats. Prior administration of sodium selenite (1.6 mg Se/kg, ip) blocked the cadmium-induced (0.84 mg Cd/kg, ip) prolongation of hexobarbital-induced hypnosis and inhibition of hepatic microsomal biotransformation of ethylmorphine or aniline. Selenium also blocked cadmium-induced reduction in microsomal cytochrome P-450 content and the microsomal binding of both ethylmorphine and aniline. However, pretreatment of rats with selenium did not prevent the inhibitory effect of cadmium (10^?6 to 10^?3m) added in vitro on either ethylmorphine or aniline biotransformation. In addition, the reduction in biotransformation of both substrates following in vivo cadmium administration was not reversed following the in vitro administration of selenium but, in fact, selenium produced further concentration-dependent decreases in drug metabolism. In additional in vitro experiments it was found that the inhibition in drug metabolism induced by in vitro additions of cadmium is not affected by similar additions of selenium when added to the incubation vessel either before or after the cadmium. Thus, for selenium to prevent the cadmium-induced inhibition of hepatic drug metabolism requires in vivo administration of selenium.     

Studies on the interaction of several boron hydrides with liver microsomal enzymes

The effects of several boron hydrides on hepatic microsomal enzymes isolated from adult male rats are described. Decaborane (B₁₀H₁₄) and the carboranes inhibited ethylmorphine N-demethylase and aniline hydroxylase activities in vitro. A decomposition product of decaborane also inhibited these microsomal enzyme systems. Pyridoxal phosphate, a coenzyme that alters the inhibitory actions of decaborane on certain enzyme systems, had no effect on the interaction of decaborane with these microsomal systems. Both decaborane and the carboranes are bound to cytochrome P-450; decaborane exhibited a modified type II spectral change, whereas o- and m-carborane exhibited type I spectral changes. Although a slight increase in aniline hydroxylase activity occurred, ethylmorphine N-demethylase activity and cytochrome P-450 content were not significantly changed when decaborane was administered daily for 3 days at doses of 5 mg/kg or 12 mg/kg. Similarly, the activity of these microsomal systems was unaltered after a single dose (12 mg/kg) of decaborane. During these studies morphologic changes of liver tissue occurred, confirming previous studies by other investigators that the liver is a site of pathology caused by decaborane. The potential utility of decaborane and other boron hydrides as pharmacologic tools in investigating hepatic microsomal drug metabolism is discussed.     

Biochemical effects of 3,5-diethoxycarbonyl-1,4-dihydrocollidine in mouse liver

3,5-Diethoxycarbonyl-1,4-dihydrocollidine (DDC) is a porphyrinogenic agent and is a powerful inducer of δ-aminolaevulinate synthetase, the first and rate-limiting enzyme of the haem-biosynthetic pathway, in mouse liver. However, DDC strikingly inhibits mitochondrial as well as microsomal haem synthesis by depressing the activity of ferrochelatase in vivo. The drug on repeated administration to female mice has been found to elicit hypertrophic effects in the liver microsomes initially, but the effects observed at later stages denote either hyperplasia or increase in polyploidal cells. The microsomal protein concentration shows a striking decrease with repeated doses of the drug. The rate of microsomal protein synthesis in vivo as well as in vitro shows an increase with two injections of DDC but decreases considerably with repeated administration of the drug. The activities of NADPH-cytochrome creductase and ribonuclease are not affected in the liver microsomes of drug-treated animals when expressed per mg of microsomal protein. DDC has also been found to cause degradation of microsomal haem, which is primarily responsible for the decrease in cytochrome P-450 content. The drug also leads to a decrease in mitochondrial cytochrome c levels due to inhibition of haem synthesis and also due to degradation of mitochondrial haem at later stages. The biochemical effects of the drug are compared and discussed with those reported for allylisopropylacetamide and phenobarbital.     

Mechanism of the drug-metabolizing enzymes' induction by 2-diethylaminoethyl-2-2-diphenylvalerate-HCl (SKF 525 A)

Repetitive administration of 2-diethylaminoethyl-2-2-diphenylvalerate-HCl (SKF 525 A) produces a biphasic effect on the pentobarbital sleeping time of rats. It causes a significant prolongation effect after one daily dose, but it significantly shortens it when more daily doses are given. Administration of three daily doses of SKF 525 A results in increased activity of ethylmorphine N-demethylase and cytochrome P-450 (P-450) content in liver microsomes while aniline hydroxylase and cytochrome c reductase activity in these preparations were not significantly increased. Repetitive administration of SKF 525 A increased [¹⁴]leucine incorporation and decreased ([¹⁴C]guanidino)arginine disappearance from microsomal proteins. Results suggest that effects on pentobarbital sleeping time and on drug metabolism resulting from repetitive SKF 525 A administration would result from increases in P-450 content which might derive from increased microsomal protein synthesis and from decreased microsomal protein degradation.     

Effects of drugs or hepatotoxins on the relation between drug-metabolizing activity and phospholipids in hepatic microsomes during choline deficiency

Choline-deficient diet was shown to alter the effects of foreign compounds on the phospholipid composition and enzyme activity of rat liver microsomes. Simultaneous treatment with phenobarbital resulted in much lower levels of individual phospholipids than those obtained from similarly treated animals kept on choline-supplemented diet although the changes were proportionately similar. The effect of carbon tetrachloride on phospholipids was masked by the deficient diet.Choline deficiency caused a decrease of drug-metabolizing activity and reduced all phospholipid fractions with the exception of phosphatidic acid. The induction of drug metabolism by phenobarbital or 4-methylcoumarin was antagonized, whereas the inhibition by carbon tetrachloride or coumarin was potentiated as were their effects on phosphatases. S-Adenosylmethionine microsomal-phospholipid methyltransferase activity was significantly increased in choline-deficient animals.The findings suggested that microsomal phospholipids might play an important role in the induction and activity of drug metabolizing enzymes and that the therapeutic effectiveness of drugs might be seriously altered during conditions of adverse health.     

Effect of Δ9-tetrahydrocannabinol administration on hepatic functions

The effects of single (10 and 50 mg/kg) and chronic (10 mg/kg/day for 21 days) i.p. administration of Δ⁹-tetrahydrocannabinol (Δ⁹-THC) on hepatic functions of rat were studied at cellular and subcellular levels. After chronic administration, (a) protein, RNA, phospholipid, cholesterol contents of liver microsomal fraction and microsomal Gl-6-Pase and Mg⁺²-ATPase activities increased significantly, (b) microsomal lipid peroxidation value decreased and (c) GOT and GPT activities of liver and serum and hepatic triglyceride contents remained unchanged. Most of the parameters studied were unaffected after single administration of the drug excepting a decrease in microsomal lipid peroxidation and increase in Mg⁺²-ATPase activity. No apparent harmful effect of the drug on hepatic functions is obvious from the present study.     

Effect of hexachlorophene, tribromsalan, trichlorcarban and cloflucarban on hexobarbital sleeping time and hepatic drug-metabolizing enzyme activity in vitro in the rat.

Oral administration of the antibactenals hexachlorophene, tribromsalan and trichlorcarban at doses of 50, 10 and 40 mg/kg, respectively, caused significant increases in hexobarbital sleeping time in male Wistar rats, while an oral dose of 40 mg/kg of cloflucarban gave only a slight increase. The four halogenated antibacterials inhibited hepatic microsomal aminopyrine N-demethylase and aniline hydroxylase activities in vitro but had no effect on hepatic microsomal NADPH-cytochrome c reductase activity. The addition of each of the antibacterials to hepatic microsomes produced a type I difference spectrum. The spectral binding constants for interaction of hexachlorophene, tribromsalan, trichlorcarban and cloflucarban with hepatic microsomal cytochrome P450 were 33, 62, 66 and 40 μM respectively. The per cent of in vitro inhibition of hepatic microsomal mixed-function oxidase activity by these agents increased with increasing incubation times. The addition of bovine serum albumin to the incubation mixtures partially reversed the inhibition of microsomal drug metabolism caused by the halogenated antibacterial agents in vitro.     

Aminopyrine: metabolism and effects in the rat after administration of inhibitors of hepatic monooxygenases.

The administration to the rat of the inhibitors of microsomal mixed function oxidase, SKF 525A and Oxine-5-sulphonic acid (OSA) caused a significant decrease of the hepatic aminopyrine N-demethylase activity, as well as an increase in the plasma levels and antipyretic activity of orally administered aminopyrine. The plasma concentrations of the aminopyrine metabolite 4-aminoantipyrine were reduced in SKF 525-A treated animals while they were slightly increased in those pretreated with OSA. These findings suggest that the in vivo changes of aminopyrine disposition and activity brought about by SKF 525-A were the result of an inhibited hepatic drug metabolism, while the effects produced by OSA were due to a more rapid intestinal absorption of aminopyrine.