Effect of a new sleep inducer, 1H-1,2,4-triazolyl benzophenone derivative 450191-S on rat liver drug-metabolizing enzyme system

The effect of a new sleep inducer, 450191-S, on the hepatic drug-metabolizing enzyme system was examined using rats and compared with those of nitrazepam and phenobarbital. Cytochrome P-450-dependent 7-alkoxycoumarin O-dealkylation activity determined using liver homogenate and isolated microsomes increased after successive oral administrations of 450191-S, and induction of the enzyme system was observed by administration of 150 approximately 200 mg/kg of the drug for at least 3 approximately 5 days. Normal activity was recovered with withdrawal of the drug for 3 approximately 5 days after induction of the hepatic enzyme system. Administration of higher amounts of 450191-S (200 approximately 600 mg/kg/day) for 3 days caused remarkable increases in the O-dealkylase and UDPGA-glucuronyltransferase activities and cytochrome P-450 and b5 contents. Similar changes in the hepatic enzyme system were observed with administration of nitrazepam (200 approximately 600 mg/kg for 3 days, p.o.) or phenobarbital (10 approximately 40 mg/kg for 3 days, i.p.). We concluded that the inducing activity of 450191-S is almost the same as that of nitrazepam, but weaker than that of phenobarbital. When the hepatic enzyme system was induced by the administration of either 450191-S or phenobarbital, the pentobarbital-induced sleeping time was shortened with increasing doses of the drugs. On the other hand, sleeping time was prolonged by the administration of another type of inducer, beta-naphthoflavone. The results suggest that the inductive pattern of 450191-S is similar to that of phenobarbital.     

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.     

Development of liver microsomal oxidations in the chick.

1. Liver microsomal preparations from chick embryos (1 day before hatching) and from 1-7 day old chicks were assayed for oxidative drug-metabolizing activity with aminopyrine, aniline and naphthalene as substrates. 2. Activities for all three substrates were highest in preparations from 1 day-old chicks. These were more than twice as active as the 7 day-old preparations and about three times as active as those from the embryos. 3. The increase in drug-metabolizing activities in newly-hatched chicks was the same for either sex and persisted for 3 days before declining towards the 7 day-old levels. 4. The developmental time-course fo the liver microsomal drug-metabolizing activities was independent of any factor in the 105 000 g supernatant fractions and of such microsomal parameters as cytochrome b5 and cytochrome P-450 content, and NADPH-cytochrome c reductase activity, but was related to changes in NADPH-cytochrome P-450 reductase levels. 5. Treatment of 7 day-old chicks with exogenous inducers, 3-methylcholanthrene or phenobarbital sodium (100 mg/kg, intraperitoneally) brought about maximal stimulation of microsomal activity as 18-24 h. The time-course of this induction was reflected by changes in microsomal cytochrome P-450 content and NADPH-cytochrome P=450 reductase activities. 6. Some induction of liver microsomal drug metabolism in 7 day-old chicks could also be brought about by injecting certain lipid-soluble egg yolk extracts.     

In vivo administration of hydroxylated phenobarbital metabolites: effect on rat hepatic cytochromes P-450, epoxide hydrolase and UDP-glucuronosyltransferase

p-Hydroxyphenobarbital and m-hydroxyphenobarbital injected intraperitoneally to rats at the dose of 80 mg/kg induced a small increase of cytochrome P-450 in crude liver homogenate (expressed as nmoles/g liver) but a decrease of cytochrome P-450 concentration in isolated microsomes (expressed as nmoles/mg microsomal protein). A similar decrease of NADPH-cyt c reductase and epoxide hydrolase specific activities was observed. Pretreatment of animals with phenobarbital metabolites did not alter the native UDP-glucuronosyltransferase, but depressed the specific activity of digitonin-treated UDP-glucuronosyltransferase towards p-nitrophenol. Gel electrophoresis of microsomes showed that p-hydroxyphenobarbital and m-hydroxyphenobarbital did not induce a net biosynthesis of proteins with molecular weight near 50,000. Qualitative examination of monooxygenase activities indicated that the administration of hydroxylated phenobarbital did not modify the catalytic characteristics of microsomes, as compared with those of control microsomes. When phenobarbital and its p-hydroxyderivative were simultaneously injected to rats, specific enzyme activities of microsomes were increased as compared with controls but remained lower than with phenobarbital alone. The qualitative characteristics of the monooxygenase system were similar to those of microsomes from phenobarbital-induced rats. It may be concluded that phenobarbital produces both a proliferation of endoplasmic reticulum and an induction of drug-metabolizing activities, whereas its hydroxylated metabolites only retain the prolifer-ative activity: thus, these two effects of phenobarbital might depend on two different molecular mechanisms.     

Altered induction response of hepatic cytochrome P-450 to phenobarbital, 3-methylcholanthrene, and beta-naphthoflavone in organotin-treated animals

The effects of tricyclohexyltin hydroxide on the induction of cytochrome P-450 in liver by phenobarbital, 3-methylcholanthrene and beta-naphthoflavone were studied. A single dose of the organotin (15 mg/kg body wt) prevented the full extent of phenobarbital induction of cytochrome P-450 from occurring; this was the case whether tricyclohexyltin was given 48 hr preceeding a single injection of phenobarbital, or administered simultaneously with the first of three daily doses of the drug. Elevation of hepatic heme oxygenase (EC 1.14.99.3) activity accompanied these changes in cytochrome P-450, but the induction of this enzyme was not affected by phenobarbital treatment. The induction of cytochrome P-448 by 3-methylcholanthrene and beta-naphthoflavone was not affected to the same extent by a single injection of tricyclohexyltin, while heme oxygenase induction was less pronounced when these cytochrome P-448 inducers were given together with the organotin. The changes in cytochrome P-450 content and in its functional activity resulting from the various treatments were further examined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of the microsomal fractions. The electrophoretic profiles illustrate clearly that the apoprotein moieties of the various cytochrome P-450 subspecies are affected to a considerable extent by treatment with tricyclohexyltin hydroxide alone, and staining in these bands was noticeably reduced even when phenobarbital was administered together with the organotin. In contrast, tricyclohexyltin failed to decreased the 3-methylcholanthrene- or beta-naphthoflavone-induced cytochrome P-450 subspecies. These data suggest that significant metabolic interactions can occur from exposure to a combination of environmental chemicals and drugs resulting in an altered metabolism of heme and cytochrome P-450.     

Xenobiotic imprinting of the hepatic monooxygenase system. Effects of neonatal phenobarbital administration

The ability of phenobarbital (PB) to neonatally "imprint" or "program" the hepatic microsomal cytochrome P-450-dependent monooxygenase system (MOS) was investigated. Phenobarbital (30 mg/kg) was administered subcutaneously to neonatal rats of both sexes on days 1-5 postpartum. Various hepatic MOS activities were measured at 6, 22, 50 and 140 days of age. Six-day-old animals of both sexes displayed the increased hepatic microsomal protein levels and enzyme activities expected from the action of phenobarbital as a transitory MOS inducer. Most of these increases dissipated by 22 and 50 days of age. However, at 140 days of age rats of both sexes that had received neonatal phenobarbital showed increased levels of cytochrome P-450, as well as both P-450 and cytochrome c reductase, ethoxycoumarin O-deethylation, glucuronyl transferase activity, in vitro covalent binding of benzo[a]pyrene to DNA and in vivo covalent binding of aflatoxin B1 to hepatic macromolecular fractions. Neonatal phenobarbital administration can alter the metabolic profile of rats in adulthood, apparently by a mechanism different from that responsible for either transitory PB induction or testosterone imprinting.     

A possible role of liver microsomal alkaline ribonuclease in the stimulation of oxidative drug metabolism by phenobarbital, chlordane and chlorophenothane (DDT)

The administration of phenobarbital (80 mg/kg), chlordane (100 mg/kg) and DDT (100 mg/kg) to adult male Wistar rats, produced a constant and early significant reduction in the liver microsomal alkaline RNase that preceded the rise of cytochrome P-450, aminopyrine oxidative demethylase, aniline hydroxylase activities and liver weight.     

A study of liver microsomal enzymes in rats following propoxur (Baygon) administration

Groups of rats were given either propoxur, were left as untreated controls, or were given phenobarbital, DDT, chlordane or toxaphene which are known to induce liver microsomal detoxification enzymes. Microsomal enzyme activity was measured by testing the ability of liver homogenates to degrade EPN (O-ethyl O-(4-nitrophenyl) phenylphosphonothioate) to p-nitrophenol. The activity of aminopyrine-N-demethylase, cytochrome P-450 and p-nitroanisole-O-demethylase in liver homogenates of rats receiving propoxur was measured. Liver microsomal detoxification enzymes were not induced by propoxur exposure.     

Effect of phenobarbital induction on galactose elimination capacity in the rat

The capacity to eliminate galactose is used clinically and experimentally as a quantitative test of liver function. Patients with liver disorders often receive drugs which induce changes in hepatic enzymes, and therefore the influence of such drugs on the galactose elimination capacity in rats was investigated.A paired experiment was performed with 11 pairs of female Wistar rats weighing about 200 g. Each pair received daily intraperitoneal injections of either phenobarbital (50 mg/kg) or isotonic saline for 8 days. The galactose elimination capacity was estimated by intravenous infusion of galactose.Phenobarbital increased significantly the weight of the liver, the lactate dehydrogenase activity, the microsomal protein, and the hepatic content of cytochrome P-450. The galactose elimination capacity was not significantly changed by phenobarbital and was related neither to the total content of cytochrome P-450 nor to the total lactate dehydrogenase activity.It is concluded that galactose elimination in rats is independent of enzyme induction by phenobarbital.     

Differential toxicity of aflatoxin B1 in male and female rats: relationship with hepatic drug-metabolizing enzymes

It is well known that distinct differences in the metabolism of xenobiotics exist between males and females of the same species. Male and female rats were treated with a single intraperitoneal dose of aflatoxin B₁ (AFB₁): 1 or 3 mg/kg for males, 3 or 6 mg/kg for females. Comparative changes in hepatic drug metabolizing and plasma enzymes had been studied. The obtained results show that, at the common dose of 3 mg/kg, AFB₁ induced an 18% mortality in males and none in females. In the plasma, total bilirubin concentration as well as the activity of transaminases and alkaline phosphatase (ALP), utilized as indicators of liver damage, were highly increased in both males and females due to the treatment with 3 or 6 mg AFB₁/kg. In the female, the plasma features rapidly declined. In contrast, in the male, the effect of AFB₁ was prolonged. Hepatic determinations revealed a pattern difference of drug metabolizing enzymes and cytochrome P-450 between males and females. The results also show that in the male, most of the drug metabolizing enzyme activities were decreased until the ninth day with the 3 mg/kg treatment. So, we observed a decrease in the activities of UDP-glucuronosyltransferase (UDPGT) with p-nitrophenol as substrate (PNP) and GSH S-transferase, 40 and 53% respectively; while the activity of epoxide hydrolase was increased up to 170%. In the meantime, the concentration of cytochrome P-450 decreased by 69%. By contrast, in the case of the female, these decreases were only 14, 43 and 23% for the UDPGT, GSH S-transferase and cytochrome P-450, respectively. Moreover, these decreases occurred only during the first three days after treatment. Thereafter, these enzyme activities significantly increased above the control values. This study suggests that the induction of detoxicating enzymes, more important in the female (72% increase in the activity of UDPGT, 480% in that of epoxide hydrolase and 42% for GSH S-transferase, may have a protective role against AFB₁ metabolites and could explain, partly, the lower sensitivity of the female to the toxic effects of AFB₁.     

Influence of drugs and chemical upon hepatic enzymes and proteins-I. Structure-activity relationship between various barbiturates and microsomal enzyme induction in rat liver.

The effect of phenobarbital, three N-phenylbarbiturates and three N-cyclohexylbarbiturates on microsomal protein content, cytochrome P-450, cytochrome b₅, aniline hydroxylase, aminopyrine demethylase, p-nitrophenol-glucuronyltransferase and the ultrastructure of hepatic cells in rat liver were studied to elucidate the influence of barbiturate structure on enzyme-inducing activity. Smooth endoplasmic reticulum increased after administration of phenobarbital, phetharbital or bucolome. Phenobarbital and phetharbital, especially phenobarbital, induced cytochrome P-450 and glucuronyl-transferase. On the other hand, the other barbiturates showed little enzyme-inducing activity. From these results, the type and spatial position of barbiturate substituents are considered important for hepatic microsomal enzyme induction. Aniline hydroxylase and aminopyrine demethylase activities changed coincidentally with cytochrome P-450 content in almost all rat livers. However, quantitative agreement of the changes in cytochrome P-450 content and drug-metabolizing activity could not be obtained, suggesting the possibility of substrate inhibition or of intrinsic inhibitors in the microsomal fraction. Bucolome, one of the N-cyclohexylbarbiturates, has been reported to be effective in the reduction of serum unconjugated bilirubin level in Gilbert's syndrome. However, in. spite of the increased smooth endoplasmic reticulum, there was a reduction in the microsomal protein content, cytochrome P-450 and glucuronyltransferase after bucolome administration. This would seem to indicate that the serum bilirubin-reducing mechanism of bucolome is different from that of phenobarbital and phetharbital.     

Effects of erythromycin on hepatic drug-metabolizing enzymes in humans

In rats, erythromycin has been shown to induce microsomal enzymes and to promote its own transformation into a metabolite which forms an inactive complex with reduced cytochrome P-450. To determine whether similar effects also occur in humans, we studied hepatic microsomal enzymes from six untreated patients and six patients treated with erythromycin propionate, 2 g per os daily for 7 days In the treated patients, NADPH-cytochrome c reductase activity was increased; the total cytochrome P-450 concn was also increased but part of the total cytochrome P-450 was complexed by an erythromycin metabolite. The concn of uncomplexed (active) cytochrome P-450 was not significantly modified and the activity of hexobarbital hydroxylase remained unchanged. We also measured the clearance of antipyrine in six other patients; this clearance was not significantly decreased when measured again on the seventh day of the erythromycin propionate treatment. We conclude that the administration of erythromycin propionate induces microsomal enzymes and results in the formation of an inactive cytochrome P-450-metabolite complex in humans. However, the concn of uncomplexed (active) cytochrome P-450 and tests for in vitro and in vivo drug metabolism were not significantly modified.     

Oxidation of 1,1,1,2-tetrafluoroethane in rat liver microsomes is catalyzed primarily by cytochrome P-450IIE1.

1,1,1,2-Tetrafluoroethane (R-134a), a nonozone-depleting alternative air-conditioning refrigerant and propellant for pharmaceutical preparations, is oxidatively defluorinated by rat hepatic microsomes. In this report we show that induction of cytochrome P-450IIE1 in rats, by pyridine administration, resulted in an 8-fold increase in the rate of R-134a metabolism by hepatic microsomes (Vmax 47 vs. 6 nmol F-/mg microsomal protein/15 min). Furthermore, when data were normalized for P-450 content, a 4-fold increase in R-134a metabolism was noted for IIE1-enriched microsome preparations. In contrast, phenobarbital and Aroclor 1254 decreased the specific activity of hepatic microsomes for this function. The microsomal content of P-450IIE1, as evaluated by Western blot, was elevated significantly only in microsomes from pyridine-treated rats. p-Nitrophenol and aniline, which are metabolized at high rates by rat P-450IIE1, decreased the rate of R-134a defluorination by hepatic microsomes; Dixon plot analysis indicated competitive inhibition with a Ki of 36 microM p-nitrophenol or 115 microM aniline. Pyridine also potently induced defluorination of R-134a catalyzed by rabbit liver microsomes. Studies with individual P-450 isozymes purified from rabbit liver showed that the phenobarbital- and polycyclic hydrocarbon-induced isozymes (IIB1 and IA2) defluorinated R-134a at negligible rates (1.9 and 0.4 nmol F-/nmol P-450/60 min, respectively). In contrast, P-450IIE1 catalyzed defluorination of R-134a at a relatively high rate (16.2 nmol F-/nmol P-450/60 min); isozyme IA1, which also is induced by nitrogen-containing heterocycles such as pyridine, was somewhat active (5.3 nmol F-/nmol P-450/60 min).(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction of Liver Microsomal Cytochrome P-450 and Associated Monooxygenases by Octachlorostyrene in the Rat

Abstract: The inducing effects of octachlorostyrene (OCS) and hexachlorobenzene (HCB), chlorinated hydrocarbon contaminants found in fish, on the microsomal cytochrome P-450 system were studied in rats. Administration of single doses of OCS and HCB at 50mg/kg intraperitoneally and higher led to increases in microsomal protein and cytochrome P-450 content, cytochrome P-450 reductase, ethylmorphine N-demethylase, 4-nitroanisole O-demethylase, acetanilide 4-hydroxylase, but not in benzo(a)pyrene hydroxylase activities. Similar patterns of induction were seen after 14 days repeated intraperitoneal or oral dosing. Sodiumdodecylsulfate polyacrylamide gel electrophoresis of microsomes from OCS and HCB treated rats showed increases in proteins similar to those found after phenobarbital (PB) induction. Under the present experimental conditions OCS and HCB were found to be PB-type inducers.     

Induction of hepatic cytochrome P-450c-dependent monooxygenase activities by dantrolene in rat

The effect of dantrolene sodium, a skeletal muscle relaxant, on drug metabolizing enzymes has been investigated after treatment of rats with a dose of 200 mg/kg for five days. We observed an induction of cytochrome P-450c and epoxide hydrolase in immunoassays and activities. An enhancement of the UDP-glucuronosyltransferase (GT1) activity was observed. We also reported a decrease of both liver cytochrome P-450 content and microsomal cytochrome P-450b dependent N-demethylation activities. On the other hand, the binding of dantrolene on microsomal cytochrome P-450 produced a type I difference spectrum, these data were obtained with liver microsomal cytochrome P-450c induced by 3-methylcholanthrene.     

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.     

The use of new methods to measure: the effect of diet and inducers of microsomal enzyme synthesis on cytochrome P-450 in liver homogenates, and on metabolism of dimethyl nitrosamine

Modified methods for measurement of cytochrome P-450 content of liver homogenates, and of formaldehyde produced in demethylation reactions are described. These methods have been used to measure cytochrome P-450 content, and metabolism of dimethyl nitrosamine in rat liver. Over 80 per cent of cytochrome P-450 present in liver homogenate of phenobarbitone treated rats could be recovered in the microsomal fraction. Feeding a low protein-low fat diet reduced the P-450 content of homogenate. and also reduced the recovery of cytochrome P-450 in the microsomal fraction to 50 per cent or less. The rate of metabolism of dimethyl nitrosamine in vivo and in vitro was increased by fasting and by phenobarbital treatment, and decreased by feeding low protein diet. Benzo(α)pyrene treatment caused a slight increase in the rate of DMN metabolism in vivo and in microsomes. The toxicity of dimethyl nitrosamine is not altered in parallel with changes in the rate of metabolism. It is suggested that the amount of toxic metabolite is more important than the rate at which it is formed.     

The effect of pretreatment with dieldrin on certain in vivo parameters of enzyme induction in mice

The present investigation was undertaken in order to study under which conditions certain in vivo parameters (LD50, sleeping time, and tissue concentrations of a given drug) would best characterize the phenomenon of enzyme induction in mice pretreated with the organohalogenated insecticide dieldrin. Five barbiturates (barbital, hexobarbital, pentobarbital, thiopental and phenobarbital) possessing different metabolic pathways were selected as the test drugs, and the influence of the route of administration (iv, ip, sc and po) upon their ultimate pharmacologic effect was evaluated.The results obtained show that dieldrin given at a dose of 25 mg/kg/day sc for 5 days, is a liver microsomal enzyme inducer based on its effect on the amount of cytochrome P-450 and the enzymatic activity of 9000 g supernatant preparations with various barbiturates used as substrates. Dieldrin significantly increased the LD50 values of phenobarbital, regardless of the route of administration. Dieldrin also raised the LD50 of hexobarbital, thiopental and pentobarbital administered by all but the iv route; however, it did not modify the LD50 of barbital. The inducer was effective in significantly reducing the duration of sleep with hexobarbital, thiopental, pentobarbital and phenobarbital via all routes of administration. The sleeping time with barbital was significantly reduced when it was given by the po route; however, it was found that dieldrin-treated mice awoke with brain concentrations of barbital that were significantly higher than those in the control animals. Dieldrin was effective in reducing the concentrations of hexobarbital in the blood and brain following all routes of administration. The same was true for pentobarbital, except in blood after an iv injection.Under suitable experimental conditions, therefore, results of tests performed in intact animals correlate well with microsomal enzyme assays, thus reinforcing evidence for enzyme induction. However, the administration of an inducer, like dieldrin, could lead to “satellite” phenomena unrelated to microsomal enzyme induction.     

Effects of gomisin A, a lignan component of Schizandra fruits, on experimental liver injuries and liver microsomal drug-metabolizing enzymes

Effects of oral administration of gomisin A, one of the components isolated from Schizandra fruits, on liver injuries induced by CCl4, d-galactosamine and dl-ethionine and on liver microsomal drug-metabolizing enzyme activities were investigated. Gomisin A suppressed the increase of serum transaminase activities and the appearances of histological changes such as degeneration and necrosis of hepatocyte, inflammatory cell infiltration and fatty deposition in each type of liver injury. The repeated administration of gomisin A (30 or 100 mg/kg, p.o., daily for 4 days) induced an apparent increase of liver weight in liver-injured and normal rats. Gomisin A decreased serum triglyceride and lipid contents of the liver in biochemical studies. Increases of microsomal cytochrome b5 and P-450, elevations of NADPH cytochrome C reductase, aminopyrine N-demethylase and 7-ethoxycoumarin O-deethylase activities and decrease of 3,4-benzo(a)pyrene hydroxylase activity per cytochrome P-450 were observed after the administration of gomisin A. In addition, gomisin A was found to enhance the incorporation of 14C-phenylalanine into liver protein and to shorten the hexobarbital-induced sleeping time. These changes caused by gomisin A were similar to those by phenobarbital. However, gomisin A is distinctly different from phenobarbital in the finding that phenobarbital lessened the survival ratio of CCl4-intoxicated mice, but gomisin A did not. Our observation suggest that gomisin A shows an antihepatotoxic action by oral application and also has hypolipidemic (mainly triglyceridemic) and liver protein synthesis-facilitating actions and that the enlargement of the liver seen with gomisin A is the adaptive hypertrophy which is due to the induction of drug-metabolizing enzymes.     

Synthesesteigerung und Abbauhemmung bei der Vermehrung der mikrosomalen Cytochrome P-450 und b-5 durch Phenobarbital

Summary Heme moieties of microsomal rat liver cytochromes P-450 and b-5 were labeled with.¹⁴C-Aminolevulini cacid. The half life of the b-5 heme radioactivity was found to be 45 hrs, that of the P-450 heme radioactivity was 22 hrs.Treatment of fed rats with Phenobarbital (80 mg/kg i.p. and 1 PB in the drinking water) for 48 hrs increased the concentration of cytochrome P-450 up to 200%, only by induced synthesis. In starved rats treated with Phenobarbital, P-450 concentration was increased up to 400%, by both induced synthesis and inhibition of breakdown.Microsomal P-450 cytochrome was determined in rat liver homogenate and in suspensions of rat liver microsomes. The amount of P-450 obtained in the isolated microsomal fraction was compared with the P-450 content in the liver homogenate. Since P-450 is a microsomal hemoprotein this relation can be correlated with the microsomal protein, in order to to calculate the real content of microsomal protein in the liver homogenate. It was found to be 65 mg/g of liver, demonstrating, that 31% of the 209 mg of total protein/g of liver consists if microsomal protein.