Protective effect of diethyldithiocarbamate and carbon disulfide against liver injury induced by various hepatotoxic agents

Diethyldithiocarbamate (DTC) and carbon disulfide (CS2), at nearly equimolar oral dose levels, protected mice against liver damage induced by carbon tetrachloride, chloroform, bromotrichloromethane, thioacetamide, bromobenzene, furosemide, acetaminophen, dimethylnitrosamine and trichloroethylene, as evidenced by the suppression of elevations in plasma GPT activity and liver calcium content, and of histopathological alterations. Both agents also prolonged hexobarbital sleeping time and zoxazolamine paralysis time in mice. DTC and SC, alone, given orally, decreased microsomal metabolism of several substrates (aniline, p-nitroanisole, hexobarbital, zoxazolamine, aminopyrine and 3,4-benzopyrene), CC14-induced lipid peroxidation, and cytochrome P-450 content. The loss of microsomal drug-metabolizing enzyme activity was also observed in the experiments in vitro using liver slices and isolated microsomes. Since a characteristic common to such diverse hepatotoxins is that they require metabolic activation before exhibiting hepatotoxicity, the protective mechanisms of DTC and CS2 may involve their interference with the process of metabolic activation of these hepatotoxins. The protective action of DTC may be mediated almost entirely through CS2 when administered orally and at least partly with parenteral administration, since, in CCl4-induced liver injury, DTC was most effective when given orally, while the action of CS2 was less dependent on the route of administration. Thus CS2 and CS2-producing agents in vivo such as dithiocarbamate derivatives and disulfiram may modify toxicological and pharmacological effects of foreign compounds by inhibiting microsomal drug-metabolizing enzyme activity in the liver.     

Protective action of diethyldithiocarbamate and carbon disulfide against acute toxicities induced by 1,1-dichloroethylene in mice

In male mice of ddY strain, a single dose of 1,1-dichloroethylene (1,1-DCE, 0.1 ml/kg, ip) produced severe renal damage at 24 hr, as evidenced by elevations in plasma urea nitrogen concentration and kidney calcium content and by massive renal tubular necrosis, while hepatic damage was less severe. A precipitous decrease in body temperature started as early as 30 min after administration of 1,1-DCE and lasted for 24 hr. Glutathione concentrations decreased in the liver and kidney, with a rebound increase seen in the former but not in the latter tissue. In carbon tetrachloride-poisoned mice, the renal toxicity of 1,1-DCE was markedly potentiated. Pretreatment with either diethyldithiocarbamate (DTC) or carbon disulfide (CS₂) blocked all of these 1,1-DCE-induced toxic manifestations in normal and carbon tetrachloride-poisoned mice. Both agents, however, did not prevent the hypothermia induced by monochloroacetic acid or chloroacetyl chloride, proposed active metabolites of 1,1-DCE. Since DTC and CS₂ inhibited hepatic and renal microsomal drug metabolizing enzyme activities (Masuda and Nakayama, 1982, Masuda and Nakayama, 1983), it is probable that the protective action of DTC and CS₂ against renal and hepatic injury induced by 1,1-DCE may be due to an inhibition of the metabolic activation of 1,1-DCE to its proposed epoxide in each organ. The action of DTC given po may be mediated by CS₂ produced in the stomach. The hypothermia induced by 1,1-DCE may not result from a direct action of 1,1-DCE per se, but by its metabolites.     

Biochemical changes in the liver of mice fed Mirex

In a study of the hepatic effects of Mirex (dodecachloroctahydro-1,3,4-methano-2H-cyclobuta[cd]pentalene), male Charles River CD-1 mice were fed 1–90 ppm Mirex in the diet for periods ranging from 1 to 70 wk. At regular intervals, heavy mitochondrial, light mitochondrial, microsomal, and soluble fractions were prepared from livers of three to six animals per group. Measurements of relative liver weight, DNA, protein, respiration, respiratory control, mitochondrial membrane permeability, mixed function oxidases (N-demethylation, aromatic hydroxylation, and cytochrome P-450), glucose-6-phosphatase, diene conjugates, and protein binding were carried out. Mirex caused an increase in relative liver weight, total liver DNA, total protein in each liver fraction, mitochondrial respiration and coupling, and mixed function oxidases. Except for DNA, each parameter increased with an increase in the level of Mirex in the diet and the duration of feeding. DNA was stimulated at all doses to 130–150% of control levels. A further rise in DNA occurred during the onset of the development of liver nodules. The action of Mirex on mitochondria occurred predominantly in the light mitochondrial fraction and resulted in a stimulation of respiration, increased coupling and a decrease in membrane permeability. Mirex added to control mitochondria (in vitro) produced none of these changes. Glucose-6-phosphatase activity was decreased with increasing levels of Mirex in the diet and duration of feeding. The concentration of microsomal diene conjugates was not affected by Mirex. Mirex was formly bound to soluble liver proteins both in vivo and in vitro, but did not displace cortisol from the cortisol receptor protein.     

Selenite-induced protection of bromobenzene hepatotoxicity in male rats

Acute treatment with sodium selenite effectively reduces bromobenzene hepatotoxicity in male, Sprague-Dawley rats. Hepatocellular damage was ameliorated as shown by marked decreases in plasma alanine and aspartate aminotransferase (ALT and AST) activities. A single dose of selenite (12.5 or 30 μmol Se/kg, ip) was administered to rats at 4, 24, 48, or 72 hr before injection of bromobenzene (7.5 mmol/kg, ip). Plasma ALT and AST activities and hepatic glutathione (GSH) content were measured 24 hr after bromobenzene treatment. As the length of time of selenite pretreatment increased, the extent of reduction of bromobenzene-induced elevation in plasma enzyme activities by selenite was enhanced, and generally, in a dose-related manner with optimal protection occurring in rats pretreated 72 hr prior with selenite. However, depletion of liver GSH by bromobenzene was not affected by selenite treatment. Hepatic GSH levels and GSH detoxication enzyme activities were measured at various intervals in rats treated with selenite alone. Selenite increased hepatic GSH content 20 to 25% at both 24 and 48 hr after injection, with a return to GSH control levels at 72 hr. Selenite treatment produced slight decreases in GSH peroxidase activity but did not alter GSH S-transferase activity. These studies suggest that the reduction of bromobenzene hepatotoxicity by selenite does not involve alterations in the activity of hepatic GSH detoxication enzymes; however, the data suggest that factors in addition to selenite-induced changes in hepatic glutathione levels are also involved.     

Ifenprodil: Protective effect in experimental cyanide poisoning

In in vivo experiments, dose-dependent protection against the lethality of cyanide was elicited by im pretreatment with ifenprodil in rats, guinea pigs, rabbits, and mice. The decline in respiration rate, blood pressure, and heart rate, and the flat electroencephalogram induced by iv administration of sodium cyanide was also reversed by previous administration of ifenprodil in these species. Methemoglobinemia was not observed after protective doses of ifenprodil in rats and ifenprodil did not affect thiocyanate formation induced by sodium cyanide and sodium thiosulfate in rats. In vitro, ifenprodil exhibited a stimulative effect on respiration of mitochondria isolated from guinea-pig liver, this effect being the most prominent with succinate as substrate and in the presence of phosphate. In addition, the inhibitory effect of potassium cyanide on the respiration was completely abolished by ifenprodil. These protective effects of ifenprodil on cyanide intoxication were also observed with both ifenprodil tartrate and hydrochloride, and tartaric acid did not exert this action. Experiments using ultraviolet absorption and proton nuclear magnetic resonance spectra did not show that ifenprodil reacts directly with free cyanide ion to trap it. The results suggest that ifenprodil prevents the signs and lethality of cyanide, and a part of the mechanism can be ascribed to antagonism at the mitochondrial level, though the mechanism is not clear at present.     

Effects of adenosine on liver cell damage induced by carbon tetrachloride

Adenosine administration delayed the fatty liver and cell necrosis induced by carbon tetrachloride without affecting the action of the hepatotoxin on protein synthesis and liver triacylglycerol release. Adenosine produced a drastic antilipolytic effect accompanied by a decrease in the incorporation of [1-14C]palmitic acid into triacylglycerols and free fatty acids of the liver. Furthermore, a decrease in the serum levels of ketone bodies was observed at early times. The nucleoside also avoided the release of intracellular enzymes and prevented the lipid peroxidation produced by carbon tetrachloride during the 4 hr of treatment. The protective action of adenosine was transient, lasting 3-4 hr, probably the time required to be metabolized. The results suggest that the antilipolytic effect of the nucleoside, the inhibition of hepatic fatty acid metabolism, and the decrease in carbon tetrachloride-induced lipoperoxidation that it produced are involved in the delayed acute hepatotoxicity induced by carbon tetrachloride.     

Simultaneous determination of piroxicam and its main metabolite in plasma and urine by high-performance liquid chromatography

A rapid and sensitive high-performance liquid Chromatographic procedure is described for the simultaneous determination of piroxicam and its main metabolite, such as 5′-hydroxypiroxicam, in plasma and urine. Acidified plasma (pH 3.0) was extracted with ethyl ether and indomethacin was used as an internal standard. The organic extract was reduced to dryness, the resultant residue redissolved in the mobile phase, and aliquots of this solution chromatographed on a Lichrosorb RP-18 (7 μm) column using a mobile phase consisting of an acetonitrile-water-acetic acid (58:38:4) mixture. The flow rate was 1.2 ml/min and the effluent was monitored at 365 nm with 0.02 aufs. The sensitivities of this method were 0.05 μg/ml levels of piroxicam and 5′-hydroxypiroxicam in the plasma and urine samples.     

Pathogenesis of hyperlipidemia induced in rabbits by methyl iodide

The metabolism of lipids and genesis of hyperlipidemia in methyl iodide-treated rabbits were investigated. Methyl iodide (57 mg/kg body weight/day) was administered sc to male Japan white rabbits on two successive days. The treatment induced a marked hyperlipidemia characterized by approximately elevenfold increase in very low-density lipoproteins (VLDL) and threefold increase in low-density lipoproteins (LDL) compared to control animals. A significant enhancement of triglyceride production in methyl iodide-treated animals by Triton methodology was demonstrated. In contrast, no change was observed in lipolytic activity in postheparin plasma of these animals. Thus hyperlipidemia induced by methyl iodide seems to be primarily due to an increased lipid synthesis. An increased insulin resistance and hyperinsulinemia were also observed in methyl iodide-treated rabbits. This change suggests that the enhancement of triglyceride production in methyl iodide-treated animals may be predominantly mediated by hyperinsulinemia due to the increased insulin resistance provoked in the animals by methyl iodide.     

Altered hepatobiliary permeability induced by Amanita phalloides in the rat and the protective role of bile duct ligation

The effect of an extract of the toxic mushroom Amanita phalloides (Fr. Secr.) on the transfer of metabolically inert, water-soluble solutes across the biliary tree epithelium of male Sprague-Dawley rats was studied by the segmented retrograde intrabiliary injection (SRII) technique. The purpose was to see if indications for a change in the permeability of the biliary tree could be obtained in vivo. This technique involved the introduction into the biliary system, through a bile duct cannula, of an initial “segment” of solution containing a radioactive marker compound followed by a volume of 0.9% saline given in excess of the biliary tree capacity. Bile flow was immediately reestablished and bile drops were serially collected. The radioactive content was determined and expressed as a percentage of the total administered dose of radioactivity. Evaluated 24 hr following the ip administration of an extract of Amanita phalloides, the biliary recoveries of [³H]mannitol, [³H]sucrose, [³H]inulin, and [³H]dextran were all found to be significantly decreased when compared to controls. These decreased recoveries were consistent with an increase in hepatobiliary permeability. This increase in permeability was not accompanied by any change in liver weight or bile flow. Bile duct ligation, 24 hr before administration of a lethal dose of the extract, protected rats against the alteration in permeability as well as the lethality. Bile duct ligation itself increased bile flow and increased the distended biliary tree capacity.     

Cytotoxicity of acetaminophen and papaverine in primary cultures of rat hepatocytes

Primary cultures of hepatocytes obtained from postnatal Sprague-Dawley rats were grown in arginine-deficient medium to inhibit fibroblastic overgrowth and to selectively isolate relatively pure cultures of parenchymal hepatocytes. The cultures were grown on collagen-coated lens paper which freely floated in the medium and thus facilitated the exchange of nutrients and waste products between the cells and the culture medium. This system of primary hepatocytes was used to study the cytotoxicity of acetaminophen, papaverine, nitrofurantoin, and sodium salicylate. Cytotoxicity was monitored by measurement of leakage of intracellular enzymes into the culture medium: argininosuccinate lyase (ASAL), lactate dehydrogenase (LDH), glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT), and acid phosphatase (AP). Cultures were treated with each of the agents in concentrations ranging from 5 × 10^?6 to 5 × 10^?3m and for durations from 1 to 24 hr. ASAL was found to be most sensitive in predicting early cell injury and AP the least sensitive. GPT, GOT, and LDH were intermittent in value and equally sensitive in evaluating cytotoxicity. No sign of cytotoxicity was observed within 3 hr of treating cultures with different concentrations of acetaminophen and papaverine. At 6 hr a significant increase in leakage of enzymes into the culture medium was observed relative to controls. After the first 3 hr the hepatotoxic agents demonstrated a time- and dose-dependence of cytotoxicity. Treatment of the cultures with acetaminophen and papaverine (5 × 10^?5m) for 12 hr resulted in ASAL leakage that was 360 and 260% of control values, respectively. In contrast, nitrofurantoin and sodium salicylate were only minimally toxic to the cultured cells. The time lag observed in the cytotoxicity of acetaminophen and papaverine may be related to the period required for metabolite(s) accumulation and saturation of detoxifying systems of the cultured liver cells.     

Ethanol-induced increase in liver tryptophan oxygenase activity in the starved rat: evidence against tryptophan mediation

A single oral dose of ethanol (4.0 g/kg) increased the activity of liver tryptophan oxygenase in starved male rats. The peak increase of 340% for the total activity and 400% for the holoenzyme activity occurred 6 hr after ethanol administration. At or after these peaks, the levels of tryptophan in plasma and brain but not in liver, decreased significantly. Plasma total tryptophan and brain tryptophan started to decrease significantly as early as 0.5-1.0 hr after the ethanol treatment, while the activity of liver tryptophan oxygenase was still at the control level. These findings suggest that not all the changes in tissue tryptophan concentrations seen after acute ethanol treatment are caused by increased liver tryptophan oxygenase activity. Prior to the increase in liver tryptophan oxygenase activity, an increase of 104 and 50% in plasma corticosterone and free tryptophan, respectively, were seen 15 min after ethanol treatment. However, the increase in liver tryptophan at this time appeared to be small (13%) and statistically insignificant. With tryptophan treatment, the initial peak levels of liver tryptophan and plasma free tryptophan required to stimulate an increase in tryptophan oxygenase activity were 170 times higher than those caused by ethanol. It was therefore concluded that increases in plasma and liver tryptophan after acute ethanol ingestion, probably mediated by the lipolytic action of ethanol, are too small to cause the increase in liver tryptophan oxygenase activity seen after ethanol administration. However, experiments with different corticosterone doses showed that ethanol-induced increases in plasma corticosterone concentrations are high enough to cause an increase in liver tryptophan oxygenase activity.     

Kinetics of cadmium-induced hepatic and renal metallothionein synthesis in the mouse

Rates of hepatic and renal metallothionein synthesis were estimated by measuring the incorporation of [³H]cysteine into metallothionein prepared from mice at various times following a single intraperitioneal injection of cadmium acetate (2 mg of Cd/kg). Tissue metallothionein concentrations were measured indirectly as a function of the total cadmium-binding capacity of the isolated metallothionein. Maximal incorporation of [³H]cysteine into hepatic metallothionein occurred 6–12 hr following cadmium exposure, while renal metallothionein synthesis was maximal after 3 hr. Incorporation of [³H]cysteine into metallothionein as well as metallothionein concentrations was greater in the liver than in the kidney. It is concluded that the liver is the primary site of cadmium-induced metallothionein synthesis.     

Kepone: cellular sites of action.

Kepone produced a dose-dependent inhibition of cellular proliferation, stimulation of respiration, and a bimodal alteration (enhancement preceding depression) of phagocytic activity in the P388D₁ “macrophage-like” cell in tissue culture. Dinitrophenol, an uncoupler of oxidative phosphorylation, similarly inhibited cellular proliferation and stimulated respiration. Kepone (IC50 = 3.5 × 10^?6M) was 77 times more potent than dinitrophenol (IC50 = 2.7 × 10^?4M) by the method of Litchfield and Wilcoxon. The dose-response curves did not deviate significantly from parallelism, suggesting that the mechanisms of toxicity may be similar. The binding of ¹⁴C-Kepone to the cells in culture was determined. After 60 min of preincubation, 1% of the Kepone was bound to the cells. Since it has been postulated that the clinical syndrome of Kepone toxicity in humans may be due to an alteration in calcium metabolism, the effect of Kepone on the kinetics of free radiocalcium distribution was determined. Kepone decreased the size of the mitochondrial exchangeable calcium pool while increasing the efflux rate constant of that organelle. The effects of Kepone on energy metabolism and cellular calcium distribution may be cellular events related to the observed in vivo toxicity.     

Tolerance, dependence and lethality in morphine-dependent mice after repeated oral administration of methadone

Mice were rendered tolerant to and dependent on morphine via a morphine pellet implantation. Three days later methadone hydrochloride was administered at a dose of 100mg/kg per os 3 hours after pellet removal and then daily for a total of 5--6 days. This dose of methadone was shown to exhibit a high efficacy for the blockade of morphine abrupt withdrawal jumping and only minimal toxicity. Under these conditions, the level of analgetic tolerance with respect to morphine and methadone and the level of dependence as measured by the naloxone ED50 were initially elevated by the morphine treatment. However, upon substitution with oral methadone these levels declined with time at a rate which did not differ from that of a group of mice receiving only water after morphine pellet removal. Despite these findings, the methadone treatment was associated with an increasing tolerance to methadone lethality during the administration of this narcotic which was nearly double that of a similarly treated water control group by the sixth day. This observation could not be explained by an elevation in the level of cellular tolerance rendered by the methadone treatment since the morphine LD50 was not elevated following identical treatment with morphine and then methadone. The significance of these results is discussed with respect to the role of methadone administration and its metabolism in the modification of tolerance and dependence.     

Toxicity of 1-phenylcyclohexene and its interaction with phencyclidine

The toxicity of 1-phenylcyclohexene (PC), a pyrolysis product of phencyclidine (PCP), and its interaction with PCP were evaluated. The ip LD50 of PC in Swiss male mice was 22 mmol/kg. Treatment of mice with PC at 2.2 mmol/kg/day, ip, for up to 7 days increased the liver/body weight ratio, which returned to normal within 7 days after PC withdrawal. Increases of 32% in serum glutamic-oxalacetic transaminase (SGOT) and 94% in serum glutamic-pyruvic transaminase (SGPT) were observed within 4 hr following the initial (Day 1) dose of PC. Smaller increases in the SGOT activity continued following Day 2 and 3 PC administrations. The SGPT activity remained elevated after these treatments. Activities of both enzymes, however, returned to normal within 24 hr following daily PC injections. No pathologic changes were observed in liver, brain, spleen, kidneys, and lungs with light microscopy. PC treatment for 4 days at 2.2 or 4.4 mmol/kg produced proliferation along with dilatation and fragmentation of the endoplasmic reticulum in liver. Scattering of ribosomes in the cytoplasm and dilatation of rough-surfaced cisternae were prominent at the higher dosage. Pretreatment of animals for 4 days with PC (1.1, 2.2, and 4.4 mmol/kg, ip) decreased pentobarbital- (60 mg/kg) induced sleeping time by 27, 64, and 80% and lowered PCP- (16.4 mumol/kg) stimulated locomotor activity by 18, 28, and 41%, respectively. Pretreatment of animals with PC for 1 hr inhibited (ED50: 2.3 mmol/kg) the PCP-induced locomotion. These results indicate that the PC treatment during a 7-day period produces some undesirable effects on liver function, which are reversible on its discontinuation. However, PC also weakens toxic effects of PCP.     

Cadmium-induced inhibition of hepatic drug oxidation in the rat: Time dependency of tolerance development and metallothionein synthesis

Experiments were undertaken to determine if a correlation existed between the time-dependent synthesis of hepatic metallothionein and the development of tolerance to the inhibition of hepatic drug oxidation elicited by cadmium in the male rat. Maximal rates of metallothionein synthesis were achieved within 2 hr after administering cadmium in a 0.21 mg Cd/kg (ip) dose. The total hepatic concentration of metallothionein, as well as the cadmium binding capacity of this protein, also increased rapidly with maximal values being observed from 8 to 67 hr after cadmium administration. Despite this rapid increase in hepatic metallothionein levels, the tolerance to the inhibition of in vivo drug oxidation induced by a challenge cadmium (0.84 mg Cd/kg) dose did not develop until 16 hr after treatment with the 0.21 mg/kg cadmium dose. Furthermore, hepatic metallothionein levels decreased from a maximum at 67 hr to approximately control levels at 336 hr. Although the tolerance to the inhibition of drug oxidation also decreased from a maximum at 72 hr a modest degree of protection was maintained even at 336 hr. Pretreatment with the 0.21 mg Cd/kg dose increased the hepatic uptake of a ¹⁰⁹Cd challenge dose (0.84 mg Cd/kg). This increase was associated with an increased ¹⁰⁹Cd binding to metallothionein in the cadmium-pretreated animals. While these data are suggestive of a role for metallothionein in tolerance development, the lack of correlation of the time course of metallothionein synthesis with the development of the tolerance would suggest that factors in addition to metallothionein may also participate.     

Protective effects of verapamil and diltiazem against inorganic phosphate induced impairment of oxidative phosphorylation of isolated heart mitochondria

The effects of verapamil and diltiazem on oxidative phosphorylation of isolated rabbit heart mitochondria were related to the experimental conditions employed. In an assay medium containing 250 mM sucrose, 1 mM pyruvate and 5 mM potassium phosphate buffer (pH 7) at 37° (sucrose medium), only a high concentration of verapamil (200–800 μM) or diltiazem (400–600 μM) affected mitochondria. State 4 respiration was stimulated, state 3 respiration was inhibited, and the ADP: O ratio was decreased by these drugs in sucrose medium. These effects resulted in a depression of the respiratory control index (RCI) and oxidative phosphorylation rate (OPR). On the other hand, in an assay medium containing 150 mM KCl, 1 mM pyruvate and 2 mM potassium phosphate buffer (pH 7) at 37° (KCl medium), the high rate of state 3 respiration and the normal value of the ADP: O ratio were not influenced significantly by diltiazem (400–800 μM) or verapamil (200–400 μM). These data indicate that neither verapamil nor diltiazem has an effect on the normal, functioning, isolated mitochondria in KCl medium. Elevation of inorganic phosphate (P₁) from 2 to 5 mM in the KCl medium induced a swelling of the mitochondria, inhibition of state 3 respiration, and a decrease in the ADP: O ratio, RCI and OPR. Under these conditions, a low concentration of verapamil (25–200 μM) or diltiazem (50–800 μM) inhibited the swelling effect of P_i and at the same time prevented the P_i-induced decrease in state 3 respiration, and the ADP: O ratio, RCI and OPR. In a medium containing 150 mM KCl, 1 mM pyruvate, 2 mM ADP and 10 μM palmitoyl-CoA, the addition of 5 mM P_i induced swelling of mitochondria and a decreased rate of state 3 respiration. Under these conditions, even a low concentration of verapamil (6–200 μM) or diltiazem (25–400 μM) inhibited swelling and prevented the inhibition of state 3 respiration. It is concluded that low concentrations of verapamil and diltiazem had no effect on unswollen heart mitochondria. An increase in the free P_i concentration induced swelling of mitochondria and resulted in an inhibition of oxidative phosphorylation, provided that the extramitochondrial potassium concentration was as high as that normally found in the cytosol. Under these conditions, a low concentration of verapamil and diltiazem was able to affect the mitochondrial membranes so as to prevent P_i-induced swelling and the related inhibition of oxidative phosphorylation.     

Correlation between dissolution rate and bioavailability of different commercial mefenamic acid capsules

A dissolution test was performed with five brands of 250 mg mefenamic acid capsule products available on the market. Three of them, the fast dissolving A and the slow dissolving D and E were subjected to a bioavailability study using a commercially available suspension as the reference. The products were administered orally in a cross-over design to 6 healthy men, and then parameters for the bioavailability were calculated from the plasma concentration-time curve. Analysis of variance indicated several significant differences among the products with respect to C_max, T_max and AUC. The relative availabilities of A, D and E were 86, 81 and 28%, respectively, with the AUC value (0-7 h) for the suspension as 100%.No correlation was observed between the in vitro dissolution rate of the drug from the capsules and the in vivo data, because the dispersing behavior of the capsule exerted a marked influence on its in vitro dissolution rate. To eliminate the influence of the capsule disintegrating process, a dissolution test was done on the contents of the capsules. A good correlation was found between the bioavailability and the dissolution rate of the drug from the capsule contents.Product E with the lowest bioavailability was passed through a 200-mesh sieve, placed in a new capsule, and tested for its bioavailabilky in humans. The AUC value was greater than that of the original product and the bioavailability was about equal to that of the suspension. The in vitro dissolution rate of the drug from the pulverized product E was also markedly increased.     

Taurolithocholate-induced increase in the intrabiliary pressure generated during retrograde intrabiliary infusion of saline in rats: Antagonism by taurocholate and glycocholate

Taurolithocholate (TLC) is known to produce cholestasis and certain bile acids antagonize this effect. This antagonistic relationship was studied by measuring intrabiliary pressure (IBP) and bile flow changes in pentobarbital-anesthetized male Sprague-Dawley rats weighing 329 ± 7 (SE) g. The IBP reflects the peak pressure generated during the retrograde intrabiliary infusion of saline at 2.3 μl/sec. When TLC was infused into the femoral vein at 0.46 μmol/min over a 35-min period, the IBP rose and the bile flow decreased. Upon stopping the infusion, IBP returned to control values in 30 min but the cholestasis persisted. Simultaneous infusion of taurocholate or glycocholate at 0.61 μmol/min with the TLC prevented the TLC-induced rise in IBP and the cholestasis. Infusion of 0.61 μmol dehydrocholate/min with the TLC did not antagonize the rise in IBP or the cholestasis. Because dehydrocholate was a more potent choleretic agent than taurocholate or glycocholate and it had no antagonistic effect on TLC-induced effects, it was evident that the antagonistic action of taurocholate and glycocholate was not due to their choleretic effect. In another experiment, an iv bolus injection of 100 μmol/kg, taurocholate and glycocholate alone produced a fall in IBP which lasted about 1 hr. Even though this latter kind of fall in IBP might have been consistent with an increase in biliary tree permeability, such an effect did not appear to play a role in the antagonistic effect of these bile salts against the taurolithocholate-induced change. The changes in IBP were likely the result rather than the cause of more fundamental alterations.     

Enzyme induction by repeated administration of tetrachlorvinphos in rats

The capability of enzyme induction in male rats was studied following the administration of tetrachlorvinphos (TCVP). A single oral dose of either 250 or 1000 mg/kg caused a more marked inhibition of true (erythrocyte) ChE than of pseudo (serum) and brain ChE activities. Dose-related increases in the activities of two hepatic microsomal enzyme activities, aminopyrine demethylase and EPN (o-ethyl O-p-nitro-phenyl phenylphosphonothioate) detoxification enzyme, were observed after 10 days of successive administration of TCVP at doses of 60 and 250 mg/kg, po. The liver to body weight ratio of rats increased on the first 7 days and then decreased on Day 10. The repeated administration of TCVP induced the enzymes responsible for the metabolism of TCVP up to 7-fold in microsomes and 1.2-fold in the supernatant fraction. The results demonstrate that the repeated application of TCVP as an insecticide may decrease its toxicity by its capacity to induce metabolizing enzymes.