The influence of cardiac output distribution on the tissue/plasma drug concentration ratio.

In pharmacokinetics, it is currently assumed that blood and interstitial spaces belong to the central compartment, when the solute is quickly equilibrated between both fluids. Taking into account that the same extracellular fluid dissolves the drug either in the plasma or in the interstitium, both drug concentrations (intra and intravascular) should be identical. However, this equality may not exist when there is a dissimilar distribution of blood flow among the organs. A closed, two-zone, three-compartment model was mathematically investigated. Compartment 1 was intravascular, and compartments 2 and 3 were extravascular. The fluid within the compartment 1 was supposed to be pushed by a pump, and to be distributed towards two different zones. One of these zones was in contact with the compartment 2, and the other with compartment 3. The drug could be exchanged between the compartments 1 and 2 or 1 and 3, by mean of first-order kinetics (k12, k21, k13, k31). It was assumed a very fast flow that assured instantaneous homogeinity of drug concentration in compartment 1. Pressure was kept constant, so an increase in the pump output distribution towards one zone is compensated by a decrease towards the other zone. At time infinite the drug concentration (C) ratio between compartments yielded: C2/C1 = k12.sigma.V1/(k21.V2) and C3/C1 = k13.(1-sigma).V1/(k31.V3), being sigma: the pump output fraction served to the zone where compartment 2 was located, and Vi: the volumes of compartments. So, at the equilibrium the concentrations are not necessarily identical between the extravascular and intravascular sites. In conclusion, as the cardiac output distribution changes due to circadian rythms and cardiovascular active drug administration, current therapeutic drug monitoring and bioequivalence studies using plasma as biologic fluid would be controversial issues.     

Characterization of mitochondrial neutral protease activity and the response of lysosomal enzymes to clofibrate feeding in rat liver.

The phosphate-inhibitable neutral protease activity of the heavy mitochondrial fraction of rat liver is of lysosomal origin. The activity is essentially due to the thiol proteinases of the lysosomes. Digitonin treatment of the mitochondrial fraction results in the release of about 85 per cent of the neutral protease activity and the residual activity has an alkaline pH optimum and is not inhibited by phosphate. Clofibrate feeding at 0.5 per cent level in the diet results in enhanced levels of lysosomal enzymes. The increase is however restricted to the lysosome-rich fraction such that the activities associated with the heavy mitochondrial fraction show a significant decrease. It is suggested that clofibrate inhibits engulfment of mitochondria by lysosomes and this results in enhanced mitochondrial protein content.     

Effect of clofibrate on plasma lipid concentration and liver malic enzyme gene expression in rats with experimental chronic renal failure

Fibrates have been used clinically to treat dyslipidemias, including chronic renal failure (CRF)-related hypertriacylgliceridemia. In addition to their effects on plasma triacylglycerol concentration, fibrates also induce hepatomegaly (due to peroxisome proliferation) and increase liver malic enzyme activity. Since most experiments regarding fibrates action have been performed on healthy animals, in this paper we compare the effect of clofibrate on: a) plasma lipid concentration; b) liver weight; c) liver malic enzyme gene expression (malic enzyme activity, malic enzyme protein level and malic enzyme mRNA abundance) in control (sham-operated) animals and rats with CRF. The data presented in this paper indicate that: a) the clofibrate treatment causes a decrease in triacylglycerol concentration both in the control and rats with CRF, however the effect of the drug was more pronounced in the latter; b) administration of clofibrate induces hepatomegaly both in the control and rats with CRF; c) the liver malic enzyme gene expression is similarly affected by clofibrate in the control and rats with CRF. It is concluded that the beneficial, therapeutic effect of clofibrate on plasma lipid concentration is more pronounced in rats with CRF, but the side effects (hepatomegaly and the increase in malic enzyme gene expression) of fibrates are essentially similar in the control and rats with CRF.     

The influence of morphine and naloxone on plasma oxytocin concentration in the rat

Subcutaneous injections of morphine decrease the plasma oxytocin level significantly in both normohydrated rats and rats dehydrated for 24 hrs. This effect of morphine is naloxone-reversible. Injections of naloxone increase the plasma oxytocin level in a time dependent manner, when the oxytocin system is stimulated by dehydration, but have no effect on basal oxytocin level. This observation indicates liberation of an endogenous opioid, during stimulation of the neurohypophysis, leading to inhibition of the oxytocin secretion. A discrepancy in the time course between the plasma oxytocin enhancing effect and the morphine reversing effect of naloxone is observed. On the basis of this observation two different opioid receptors are suggested to be involved in the effect of naloxone on the neurohypophysis.     

The effect of liver cirrhosis on the regulation and expression of drug metabolizing enzymes

Cirrhosis is the end stage of many forms of liver pathologies including hepatitis. The liver is known for its vital role in the processing of xenobiotics, including drugs and toxic compounds. Cirrhosis causes changes in the architecture of the liver leading to changes in blood flow, protein binding, and drug metabolizing enzymes. Drug metabolizing enzymes are primarily decreased due to loss of liver tissue. However, not all enzyme activities are reduced and some are only altered in specific cases. There is a great deal of discrepancy between various reports on cytochrome p450 alterations in liver cirrhosis, likely due to differences in disease severity and other underlying conditions. In general, however, CYP1A and CYP3A levels and related enzyme activities are usually reduced and CYP2C, CYP2A, and CYP2B are mostly unaltered. Both alcohol dehyrogenases and aldehyde dehydrogenases are altered in liver cirrhosis, although the etiology of the disease may determine the expression of alcohol dehydrogenases. Glucuronidation is mainly preserved, but there are a number of factors that determine whether glucuronidation is affected in patients with liver cirrhosis. Low sulphation rates are usually found in patients with liver disease but a decrease in sulfatase activity compensates for the decrease in sulphation rates. In all cases, a reduction in drug metabolizing enzyme activities in liver cirrhosis contributes to decreased clearance of drugs seen in patients with liver abnormalities. The reduction in drug metabolizing enzyme activity must be taken into consideration when adjusting doses, especially in patients with severe liver disease.     

Effects of clofibrate,bezafibrate, fenofibrate and probucol on plasma lipolytic enzymes in normolipaemic subjects

Summary Ten male, normolipaemic, non-obese subjects were given clofibrate 2g daily, fenofibrate 300 mg daily, bezafibrate 600mg daily and probucol 1g daily for eight days, in a crossover study with a wash-out period of 4–8 weeks between each drug regimen. Clofibrate, fenofibrate and bezafibrate caused a significant decrease in serum triglycerides, total cholesterol and LDL-cholesterol concentrations. Probucol caused a significant increase in serum LDL-cholesterol concentration. Serum HDL-cholesterol concentration was significantly increased by bezafibrate and significantly decreased by probucol. All drugs but probucol led to a significant rise in the activity of the plasma lipoprotein lipase; there was not a significant increase in the activity of plasma hepatic lipase after any drug. The activity of plasma lecithin: cholesterol acyltransferase was significantly increased by fenofibrate and probucol. Analysis of the correlations between serum lipids and plasma lipolytic enzymes suggests that the mechanism of the hypolipidaemic action of clofibrate and bezafibrate might be related to increased catabolism of triglyceride-rich particles; that of fenofibrate and probucol was less clear and might be multifactorial in origin.     

The stability of the drug metabolising enzymes of liver microsomal preparations

The stability of the drug metabolising enzymes of various preparations of rat liver microsomes has been investigated.Four reactions have been studied: (1) the N-demethylation of morphine, (2) the N-demethylation of codeine, (3) the O-demethylation of codeine and (4) the hydroxylation of diethyl tryptamine.The rates of all these reactions are influenced by temperature and an absolute requirement for oxygen and the enzyme activity is linear only over a 30 minute period when the incubation mixture is shaken in air at 37.5 °C.The causes of the instability of these enzyme systems are discussed.     

The development of drug metabolising enzymes and their influence on the susceptibility to adverse drug reactions in children

Altered drug disposition in the developing child occurs as a result of both biochemical and physiological changes. The clearance of many drugs is dependent on their biotransformation in the liver and small bowel and consequently is developmentally determined by a number of factors including both the activity and abundance of enzymes involved in Phase 1 and 2 drug metabolism. Altered drug metabolism can lead to the development of adverse effects in neonates and small infants that are not generally seen in the adult population. For instance, the altered metabolism of sodium valproate in children under 3 years of age is thought to be responsible for a higher incidence of hepatotoxicity, the impaired metabolism of chloramphenicol in neonates has resulted in the grey baby syndrome (cyanosis and respiratory failure) and metabolic acidosis following the use of propofol in the critically ill child may be due to altered drug metabolism. This paper reviews the potential contribution of the ontogeny of a number of drug metabolising enzymes including cytochrome P450 and glucuronoslytransferases to the development of adverse drug reactions in children.     

The influence of plasma butyrylcholinesterase concentration on the in vitro hydrolysis of cocaine in human plasma

In humans, the plasma enzyme butyrylcholinesterase, BChE (EC 3.1.1.8), mediates the in vivo plasma hydrolysis of cocaine to the pharmacologically inactive metabolite ecgonine methyl ester, EME. This enzyme has been purified from human plasma to investigate the potential as a treatment for cocaine intoxication. Cocaine (2.1 μg mL⁻¹) was incubated in plasma with a BChE concentration in the normal range (3.02 μg mL⁻¹) and in plasma with enhanced BChE concentrations of 9.14, 20.8 and 37.8 μg mL⁻¹, respectively for time periods up to 120 min. Cocaine and the hydrolytic products, ecgonine methyl ester and ecgonine, were quantified simultaneously by gas chromatography-mass spectrometry (GC-MS). The enhancement of plasma BChE concentration resulted in a dramatic increase in the rate of hydrolysis of cocaine. There was a stoichimetric conversion of cocaine to the inactive hydrolysis product, ecgonine methyl ester. Accordingly, the half-life of cocaine in plasma decreased significantly with enhanced BChE concentration. At plasma BChE concentrations of 3.02, 9.14, 20.8 and 37.8 μg mL⁻¹, half-life values of 116, 35.8, 21.4 and 9.0 min, respectively were observed. The marked reduction in cocaine half-life provides evidence supporting the potential therapeutic use of BChE for the treatment of cocaine intoxication. © 1998 John Wiley & Sons, Ltd.     

Effects of treatment with the anti-parasitic drug diminazene aceturate on antioxidant enzymes in rat liver and kidney

Diminazene aceturate (DA) is the active component of some trypanocidal drugs used for the treatment of animals infected with trypanosomosis and babesiosis. Residues of DA may cause hepatotoxic and nephrotoxic effects. Therefore, the purpose of this study was to investigate the occurrence of oxidative stress, i.e., changes in the antioxidant defense system of rats treated with a single dose of 3.5 mg kg^?1 of DA. All treatments were intramuscularly administered, and evaluations were performed on days 7 and 21 post-treatment (PT). Liver and kidney samples were collected and evaluated by histopathology and oxidative stress parameters (thiobarbituric acid-reactive species, catalase, superoxide dismutase, carbonyl, non-protein thiols, and reduced glutathione). Finally, blood was collected to determine seric DA concentration. Superoxide dismutase (SOD) and catalase (CAT) activities in liver and kidney of rats were dramatically inhibited (p?<?0.05) compared to the control group on day 21 PT. This difference is related to the concomitant increase (p?<?0.05) in malondialdehyde (MDA) content, which was identified by an increase in thiobarbituric acid-reactive species (TBARS) levels. The carbonyl levels did not differ between groups (p?>?0.05). Both non-protein thiols (NPSH) and glutathione (GSH) levels in liver and kidney decreased (p?<?0.05) on day 21 PT. Chromatographic analyses showed lower levels of DA on day 21 PT compared to day 7 PT. A negative correlation was observed between DA concentration in serum and lipid peroxidation in liver and kidney tissues on 21 days PT. Histopathology revealed vacuolar degeneration in liver and kidney samples on day 21 PT. Our findings indicate that DA could cause oxidative damage to liver and kidney of rats.     

The effect of aspartame on the activity of rat liver xenobiotic-metabolizing enzymes

Male, Wistar rats were administered aspartame (40 or 4000 mg/kg body weight) in their diet for 90 days. By 45 days, the activities of three microsomal enzymes, epoxide hydrolase, carboxylesterase, and p-nitrophenyl-UDP-glucuronosyltransferase, were significantly increased in rats consuming 4000 mg/kg of aspartame. By 90 days, however, the activity of the xenobiotic-metabolizing enzymes of the rats given aspartame did not differ significantly from the activity of control animals. From these results, we conclude that the consumption of aspartame does not substantially alter the function of the hepatic microsomal enzymes which protect the organism from foreign compounds found in its environment and food.     

Effect of ethanol and clofibrate on the activity of lipid catabolism enzyme systems in rat liver

Male rats were fed ethanol as a constituent of an isocaloric diet. Ethanol administration caused hypercholesterolemia and accumulation of lipids in the liver. However, it did not alter enzymatic activity of fatty acids and cholesterol catabolism in the organ. Addition of the hypolipemic agent clofibrate to the ethanol-containing diet reduced the adverse effects of ethanol on lipid metabolism due to activation of peroxisomal and mitochondrial enzymes involved in oxidative degradation of lipids in the liver cell.     

The influence of n-hexane treatment on the glucuronic acid pathway and activity of some drug-metabolozing enzymes in guinea-pig

Treatment of guinea-pigs with n-hexane for 8 days enhanced the in vitro glucuronyl conjugation of p-nitrophenol. This induction was accompanied by a significantly enhanced microsomal protein content. However, the in vitro rates of the p-hydroxylation of aniline and the N-hemethylation of aminopyrine were slightly decreased and unchanged, respectively, during this treatment. An increased urinary excretion of d-glucuronic acid and d-glucaric acid paralleled the induction of UDPglucuronyltransferase. The excretion of glucuronides in the urine was already enhanced within 24 hr after the first dose of n-hexane. The conclusion is drawn that n-hexane may be considered as a specific inducer of the glucuronidation system.     

The influence of anaesthesia on plasma spermidine concentration and renal excretion in rats

Anaesthesia with ether or a mixture of fentanyl and fluanisone diminished the clearance of infused spermidine from plasma in WAG/Rij rats considerably. The renal excretion of infused spermidine in unanaesthetized animals was only very small. The diminished plasma clearance of infused spermidine in anaesthetized animals therefore cannot be explained by loss of renal excretion.     

The influence of vancomycin concentration and the pH of plasma on vancomycin protein binding.

A review of numerous studies of the protein binding of vancomycin suggests major discrepancies among their results. The reported percent protein binding of vancomycin varies from 0% to 98%. The influence of pH and concentration on the protein binding of vancomycin was investigated in this study. There was a significant difference (p < 0.001) in percent protein binding in vancomycin-spiked plasma samples across the pH range of 7.0-8.0. There was no significant difference (p > 0.05) in percent protein binding in vancomycin-spiked plasma samples across the concentration range of 2-80 mg/L. It is likely that some of the variation reported to date may be due to a lack of control of pH during the measurement of protein binding of vancomycin.     

The influence of vitamin E and methionine on the activity of enzymes and the morphological picture of liver of rats intoxicated with sodium fluoride

The aim of this study was to investigate the effects of vitamin E and methionine on the activity of enzymes regulating carbohydrate metabolism and enzymes associated with glutathione as well as to examine the morphology of the liver in rats exposed to sodium fluoride.The study was conducted in 18 male rats of Wistar strain. The rats were divided into three groups: a control group, which received distilled water and two experimental groups, which received sodium fluoride (10 mg/kg of body mass/24 h) in water solution. Animals in the second experimental group received 3 mg of vitamin E/rat/24 h and 2 mg methionine/rat/24 h. The experiment lasted 35 days. In supernatants obtained after homogenization of rat liver slices, the activity of the following enzymes was assayed: fructose-1,6-biphosphate aldolase (ALD) malate dehydrogenase (MDH), lactate dehydrogenase (LDH), sorbitol dehydrogenase (SDH) the activity of glutathione peroxidase (GPx), glutathione transferase (GST) and glutathione reductase (GR). Pathomorphological evaluation was conducted on preparations made by standard paraffin method, followed by staining with hematoxylin and eosin. The administration of antioxidants counteracted changes in the activity of the enzymes and the morphological abnormalities of the liver induced by NaF. Antioxidants may be important in preventing toxicity of fluoride compounds.