Sulfonamide Acetylation in Isolated Rat Liver Cells

Abstract: Primary suspensions of isolated liver cells, prepared from rat livers perfused with Ca⁺⁺ free buffer and 0.05% collagenase, were used for studies of sulfadimidine and sulfanilamide uptake and metabolism at various temperatures (29°–41°) and pH (6.4–7.8). The intracellular: extracellular ratio for sulfanilamide was found to be insensitive to both temperature and pH variations, while the corresponding ratio for sulfadimidine was pH dependent but insensitive to temperature variation. Decreasing pH increased the cell content of sulfadimidine. Sulfanilamide was metabolized by acetylation only, while sulfadimidine gave rise to several metabolites. The rate of sulfanilamide acetylation in primary cell suspensions was of the same order of magnitude as the acetylation rate of sulfanilamide published previously for the intact organ. Sulfanilamide was acetylated at the highest rate in the pH-region from 7.0 to 7.5, while sulfadimidine was metabolized most rapidly between pH 6.7 and 7.3. At pH 7.5 sulfadimidine was metabolized at a rate only 35% of the rate at pH 7.3. The acetylation rate of both drugs increased with increasing temperature, approximately 5% per degree celcius, and exhibited a Q₁₀ of 1.5.     

Sulfonamide Acetylation in Isolated Rabbit and Rat Liver Cells

Abstract: Suspensions of isolated liver cells were prepared from rabbit livers perfused with Ca⁺⁺ -free buffer and 0.05% collagenase. Primary cell suspensions (containing both parenchymal and non-parenchymal liver cells) metabolized sulfadimidine and sulfanilamide at first-order kinetics for at least 2–3 hrs. Suspensions of purified rabbit liver parenchymal cells had an equal metabolic capacity, and it could be demonstrated that the metabolic rate of both sufadimidine and sulfanilamide was correlated to the amount of viable parenchymal cells in suspension. Suspensions of non-parenchymal cells were lacking the ability to metabolize both drugs. By means of homogenates of purified rabbit and rat liver cells, it could be demonstrated that the enzyme N-acetyltransferase was located in the cytosolic fraction of the parenchymal cells. It was concluded that the cytosolic fraction of the liver parenchymal cells is the main site of sulfonamide acetylation in both rabbit and rat.     

十一酸睾酮自微乳制剂的大鼠体内药代动力学研究

目的制备十一酸睾酮自微乳化制剂,并对其大鼠体内药代动力学进行研究。方法采用血清睾酮放免法测定给药后大鼠体内血清睾酮水平的变化,并计算药代动力学参数。结果十一酸睾酮原料药混悬液基本没吸收,而自微乳制剂和市售Andriol药物的吸收大大提高。以Andriol为参比制剂,自微乳制剂的相对生物利用度为96.4%。结论自微乳化给药系统能提高脂溶性药物十一酸睾酮的吸收。     

The influence of moderate and chronic exercise training on the pharmacokinetics of procainamide and N-acetylprocainamide

The effect of moderate and prolonged exercise on the disposition and metabolism of drugs has not been extensively examined. The present study examined the effect of exercise training on the pharmacokinetics of procainamide and its active metabolite, N-acetylprocainamide. Male Sprague Dawley rats were randomly assigned to three testing groups: (1) sedentary, (2) 4 weeks of exercise training and (3) 8 weeks of exercise training. Treadmill speed and exercise duration were gradually increased, reaching a final rate of 24 m min⁻¹ for an hour by the end of the 4-week or 8-week period. Sedentary and exercise trained rats received a single i.p. dose of procainamide (100 mg kg⁻¹). Serial blood samples were collected over a 10 h period and plasma samples were analysed by an UV-HPLC method. Noncompartmental analysis was performed to estimate the pharmacokinetic parameters. The t_1/2 of procainamide was significantly (p <0.05) higher in the 8 week exercise group (331 min) as compared to the sedentary group (77 min). In addition, there was a significant reduction in the amount of N-acetylprocainamide formed after 8 weeks of exercise (AUC_NAPA=739 ng mL⁻¹ min⁻¹). Results of this study suggest that prolonged exercise (8 weeks of training) alters the pharmacokinetics of procainamide by modifying the amount of active metabolite formed. © 1998 John Wiley & Sons, Ltd.     

Effect of Tilorone Hydrochloride on Hepatic Disposition of Sulphobromophthalein (BSP) in the Rat

1. Biliary excretion of sulphobromophthalein (BSP) was studied in male rats after oral administration of tilorone HCl, an anti-viral and anti-tumour agent.

2. The stimulation of bile flow by BSP was decreased 1?h after tilorone administration; this decrease was no longer apparent 24?h later but a fall of basal bile flow was noted at that time. No changes in bile flow were observed 7 days after this single dose.

3. Repeated dosing with tilorone produced a dose-dependent increase in hepatic concentration of unchanged and metabolized tilorone. This was associated with a dose-dependent decrease of bile formation and BSP excretion. Bile acid excretion was depressed as well.

4. BSP metabolism was not significantly affected by tilorone administration.     

Disposition of Sulfamethazine and N-Acetylsulfamethazine in the Rat

Pharmaceutical Research -     

Serum Levels and Electrophysiological Effects of N-Acetylprocainamide as Compared with Procainamide in the Dog Heart in situ

Abstract The electrophysiological effects of procainamide and its major metabolite N-acetylprocainamide were tested and compared on the heart of the anaesthetized dog by means of His bundle electrography and programmed electrical stimulation. Both drugs exerted a negative chronotropic effect. They also increased intra-atrial and intraventricular conduction times; procainamide was, however, the more potent of the two drugs. In contrast to procainamide, N-acetylprocainamide did not increase His-Purkinje and atrioventricular nodal conduction times, and at the lowest dose employed, atrioventricular nodal conduction times were decreased during atrial pacing. Both drugs increased the functional and effective refractory period of the right atrium and ventricle. N-acetylprocainamide increased the functional refractory period of the atrioventricular node, but to a lesser extent than procainamide.     

The uptake and elution of lignocaine and procainamide in the hindquarters of the sheep described using mass balance principles

Mass balance principles were used to describe the uptake and elution of lignocaine (lidocaine) and procainamide in the hindquarters of the sheep. Each of four sheep received a right atrial infusion of either lignocaine · HCl (2.7 mg/min) or procainamide · HCl (5.5mg/min) for 180 min. Paired arterial and inferior vena cava (draining the hindquarters) blood samples were taken at 20-min intervals during the infusion and for 180 min after the infusion. Lignocaine and procainamide mean total body clearances were 2.9 L/min (SD 1.1) and 1.3 L/min (SD 0.2), respectively. An index of the uptake and elution of these drugs in the hindquarters was estimated from the net drug mass per unit hindquarter blood flow;indirect evidence suggested that hindquarter blood flow was constant. All the net mass/flow of procainamide that was taken into the hindquarters during the infusion also eluted after the infusion, demonstrating reversible distribution into the tissues. However, uptake of procainamide was still occurring when blood concentrations were constant, indicating that the concentrations of procainamide in the hindquarters were not in equilibrium with the inferior vena cava concentrations. Lignocaine did not reach constant blood concentrations during the infusion and showed no tendency to reach arteriovenous equilibration; an arteriovenous difference of 22%(SD5%) across the hindquarters was measured during the last 60 min of the infusion. By 180 min after the lignocaine infusions, 79% (SD 8%) of the lignocaine net mass/flow had not eluted from the hindquarters when arterial and venous lignocaine concentrations were not significantly different. This drug could remain uneluted due to metabolism and/or avid tissue binding, and presents difficulties in the interpretation of pharmacokinetic data whether based on arterial or venous blood sampling.This work was funded by a grant from National Health and Medical Research Council of Australia. RNU was funded by a National Health and Medical Research Council Biomedical Postgraduate Scholarship.     

The Effect of Amiodarone on Theophylline Pharmacokinetics in the Rat

Amiodarone is an investigational antiarrhythmic agent which has been implicated in reducing the activity of the hepatic mixed-function oxidase system. To evaluate this effect further, two groups of six male Sprague–Dawley rats each received theophylline (6 mg/kg, iv) preceded by either normal saline or amiodarone HC1 (100 mg/kg, iv). Blood samples were obtained serially for a period of 6 hr and the sera were assayed for theophylline by high-pressure liquid chromatography (HPLC). In rats pretreated with amiodarone, a significant 45% reduction in the mean (± SD) systemic clearance [0.057 (0.010) vs 0.031 (0.004) liter/hr/kg, P < 0.001] and a greater than 100% increase in the mean elimination half-life [2.03 (0.46) vs 4.29 (0.71) hr, P < 0.001] of theophylline were observed. These data demonstrate an acute inhibitory effect of amiodarone on the hepatic microsomal enzyme system.     

Effect of Hydralazine on the Elimination of Antipyrine in the Rat

The concomitant administration of hydralazine with metoprolol or propranolol substantially increases the oral bioavailability of these beta-blockers, presumably via reduction of the first-pass effect. It has been suggested that this effect may be secondary to a decrease in the intrinsic clearance of propranolol, possibly by inhibition of oxidative metabolism. To examine the possibility that hydralazine alters oxidative metabolism in vivo, the effect of hydralazine on the pharmacokinetics of antipyrine was examined in the rat. The oral administration of hydralazine hydrochloride, 7.5 mg/kg, 15 min prior to antipyrine administration reduced antipyrine clearance from 9.66 ± 1.18 to 8.19 ± 0.76 ml/min/kg (P < 0.05). Hydralazine was observed to cause substantial hypothermia. The study was repeated in temperature-regulated animals and no alteration in antipyrine clearance was found. Two doses of hydralazine in temperature-regulated rats also failed to alter antipyrine clearance. Thus, it appears that the effect of hydralazine on antipyrine clearance is secondary to the hypothermic effect of hydralazine and not due to a direct inhibition of cytochrome P-450-mediated enzyme activity.     

Effect of Acetyl Derivatives of some Sympathomimetic Amines on the Blood Pressure of the Rat

Abstract The effect of five sympathomimetic amines and some of their acetyl derivatives on the blood pressure of the rat was determined on the left carotid artery. After pretreatment with chlorisondamine (1 mg/kg subcutaneously) the blood pressure rise by sympathomimetic amines and their acetyl derivatives was compared with that of adrenaline. If the potency of adrenaline is specified as 100, the potencies of the other drugs are phenylephrine (metaoxedrinum, NFN) 37, tyramine 1.1, O-acetyltyramine 0.52, amphetamine 0.50, O-diacetyl-phenylephrine 0.25, ephedrine 0.23, O-acetylephedrine 0.02, N-acetylphenyl-ephrine 0.01. The effects of N-acetyltyramine, N-acetylephedrine and N-acetyl-amphetamine are even weaker. Reserpine 5.0 or 0.05 mg/kg intraperitoneally 24 hours before the experiment increased the blood pressure rise by the directly acting sympathomimetic amines and their acetyl derivatives, but decreased the effects of the indirectly acting drugs. After treatment with phenoxybenzamine (2 mg/kg intraperitoneally), adrenaline exhibited the greatest blood pressure decrease and the effects of the other drugs in descending order: orciprenaline, O-acetyltyramine, phenylephrine, ephedrine, amphetamine, O-diacetylphenyl-ephrine and O-acetylephedrine. Tyramine did not show any blood pressure decrease. The blood pressure decrease by sympathomimetic amines and by their acetyl derivatives was probably due to β-receptor stimulation because it was prevented by propranolol. The N-acetyl derivatives recembled their parent drugs with regard to the immediate onset and short duration of their effects. The O-acetyl derivatives exhibited slower onset and longer duration of effect than their parent drugs. Physostigmine-pretreatment diminished the rise in blood pressure by O-acetyltyramine, but the effect of tyramine remained unchanged.     

Effect of Isoflurane Anesthesia on Antipyrine Pharmacokinetics in the Rat

Pharmaceutical Research -     

Toxicity and Response Evaluation of the Interferon Inducer Poly ICLC Administered at Low Dose in Advanced Renal Carcinoma and Relapsed or Refractory Lymphoma: A Report of Two Clinical Trials of the Eastern Cooperative Oncology Group

Purpose: Phase II studies were conducted toevaluate the safety and efficacy of the interferon inducerPoly ICLC at low doses in advanced renal cancer and relapsedor refractory lymphoma. Patients and methods:Twenty-nine patients with advanced renal carcinoma and elevenpatients with lymphoma were treated with poly ICLC. Patientsreceived 0.25 mg/m² of poly ICLC intravenouslytwice weekly three days apart until progression orunacceptable toxicity. Results: There were noobjective responses. Six patients with renal carcinoma hadstable disease as best response with one patient receiving 62weeks of therapy. Toxicity included grade 3 anemia in 8patients and grade 4 anemia in one patient. All patients wereanemic prior to entry with a median grade 2 anemia atbaseline. Grade 4 neutropenia, thrombocytopenia and injectionsite pain occurred in one patient each. Grade 3 fever, chillsor fatigue occurred in four, three, and three patientsrespectively. Any grade fever occurred in 10 patients(25.6%) and any grade chills occurred in 9 patients(23.1%). Conclusion: Poly ICLC at this doseand schedule is well tolerated in both patient populations andis inactive in renal carcinoma.     

Effects of cytochrome P450 inducers and inhibitors on the pharmacokinetics of intravenous furosemide in rats: involvement of CYP2C11, 2E1, 3A1 and 3A2 in furosemide metabolism

Objectives It has been reported that the non‐renal clearance of furosemide was significantly faster in rats pretreated with phenobarbital but was not altered in rats pretreated with 3‐methylcholanthrene. However, no studies on other cytochrome P450 (CYP) isozymes have yet been reported in rats. Method Furosemide 20 mg/kg was administered intravenously to rats pretreated with various CYP inducers –3‐methylcholanthrene, orphenadrine citrate and isoniazid, inducers of CYP1A1/2, 2B1/2 and 2E1, respectively, in rats – and inhibitors – SKF‐525A (a nonspecific inhibitor of CYP isozymes), sulfaphenazole, cimetidine, quinine hydrochloride and troleandomycin, inhibitors of CYP2C6, 2C11, 2D and 3A1/2, respectively, in rats. Key findings The non‐renal clearance of furosemide was significantly faster (55.9% increase) in rats pretreated with isoniazid, but slower in those pretreated with cimetidine or troleandomycin (38.5% and 22.7% decreases, respectively), than controls. After incubation of furosemide with baculovirus‐infected insect cells expressing CYP2C11, 2E1, 3A1 or 3A2, furosemide was metabolized via CYP2C11, 2E1, 3A1 and 3A2. Conclusions These findings could help explain possible pharmacokinetic changes of furosemide in various rat disease models (where CYP2C11, 2E1, 3A1 and/or CYP3A2 are altered) and drug–drug interactions between furosemide and other drugs (mainly metabolized via CYP2C11, 2E1, 3A1 and/or 3A2).     

Effects of enzyme inducers and inhibitors on the pharmacokinetics of intravenous omeprazole in rats

A series of experiments using various inducers and inhibitors of the hepatic microsomal cytochrome P450 (CYP) isozymes were conducted to find CYP isozymes responsible for the metabolism of omeprazole in male Sprague-Dawley rats. Omeprazole, 20 mg/kg, was administered intravenously. In rats pretreated with SKF 525-A (a nonspecific CYP isozyme inhibitor in rats), the time-averaged nonrenal clearance (Cl(nr)) was significantly slower (77.1% decrease) than that in untreated rats. This indicated that omeprazole is metabolized via CYP isozymes in rats. Hence, rats were pretreated with various enzyme inducers and inhibitors. In rats pretreated with 3-methylcholanthrene and dexamethasone (main inducers of CYP1A1/2 and 3A1/2 in rats, respectively), the Cl(nr) values were significantly faster (43.8% and 26.3% increase, respectively). In rats pretreated with troleandomycin and quinine (main inhibitors of CYP3A1/2 and 2D1 in rats, respectively), the Cl(nr) values were significantly slower (20.9% and 12.9% decrease, respectively). However, the Cl(nr) values were not significantly different in rats pretreated with orphenadrine, isoniazid and sulfaphenazole (main inducers of CYP2B1/2 and 2E1, and a main inhibitor of 2C11, respectively, in rats) compared with those of respective control rats. The above data suggested that omeprazole could be mainly metabolized via CYP1A1/2, 3A1/2 and 2D1 in male rats.     

The Effect of Antineoplastic Drugs on the Pharmacokinetics of Antipyrine in the Rat

Abstract: The pharmacokinetics of antipyrine was investigated in individual rats pretreated with cyclophosphamide, 5-fluorouracil and methotrexate. Before oral dosing a complete emptying of the rat stomach was obtained by 24 hours of fasting and prevention of coprophagy. Antipyrine was given intravenously via a cannula in an inguinal vein and repeated samples of blood were drawn from a cannula in an inguinal artery. Systemic availability of oral antipyrine was studied in rats given the ¹⁴C-labelled drug intravenously and the ³H-labelled drug orally after pretreatment with cyclophosphamide. The log plasma concentration versus time curve of antipyrine given orally showed a short absorption and distribution phase followed by a linear elimination phase. Peak antipyrine concentrations were reached 3–6 minutes after oral dosing in control rats. The rate of absorption of antipyrine was moderately decreased by methotrexate. All drugs increased the area under the curve (AUC) of antipyrine. The systemic availability of oral antipyrine after cyclophosphamide pretreatment (0.88) was not changed, but the metabolic clearance of the drug was reduced. The apparent elimination rate constant was decreased by methotrexate and the apparent volume of distribution was decreased by cyclophosphamide and 5-fluorouracil. The results indicate that antineoplastic agents may change drug kinetics in different ways in rats.     

Effect of Amiodarone and Desethylamiodarone on the Pharmacokinetics of Antipyrine in the Rat

The effect of amiodarone on hepatic drug metabolism in vivo was examined in the rat using antipyrine as a model substrate. Pretreatment with oral amiodarone hydrochloride, 100 mg/kg/day, for 5 days resulted in a 19% reduction in antipyrine clearance and a 22% increase in half-life. The administration of single oral doses of amiodarone hydrochloride, 100 mg/kg, 1 or 5 hr prior to antipyrine administration had no significant effect on antipyrine pharmacokinetics. The administration of a single intravenous dose of amiodarone hydrochloride, 50 mg/kg, reduced antipyrine clearance by 32% and increased the half-life by 46%. The desethyl metabolite of amiodarone was also found to reduce antipyrine clearance (21%) after a single oral dose of 100 mg/kg.     

The influence of pyruvic acid on the pharmacokinetics of sulphadiazine in rabbits

During the past few years, acetylation polymorphism has been shown to be a proven, established fact, and N-acetyltransferase, an enzyme that transfers an acetyl group to the substrate, has been recognized as the main factor in acetylation polymorphism. In a recent study, a significant difference between the acetylation phenotype and plasma pyruvic acid (PA) concentration in rabbits was found. In this report, the influence of PA on the pharmacokinetics of sulphadiazine (SDZ), a drug that has been used in pharmacogenetic studies of acetylation, was studied. By using a loading dose of 300 mg kg^?1, and an infusion rate of 7.5 mg min^?1 of kg^?1 of PA, the concentration of PA reached a steady state (C_ss∽100 μg mL^?1) in 30 min. During PA infusion in rapid-acetylation rabbits, no significant changes were found in any of the pharmacokinetic parameters for SDZ. However, differences were found in the β half-life, AUC, clearance, and k₁₀ of SDZ in slow acetylators: the β half-life decreased from 115.74 ± 12.47 min to 62.96 ± 4.36 min (p < 0.001); AUC decreased from 10 617.38 ± 1179.81 μg mL^?1 to 6217.14 ± 391.32 μg min mL^?1 (p < 0.001); clearance increased from 0.0044 ± 0.0008 L min^?1 kg^?1to 0.0068 ± 0.0007 L min^?1 kg^?1 (p < 0.001); and k₁₀ increased from 0.0090 ± 0.0009 min^?1 to 0.0193 ± 0.0028 min^?1 (p < 0.005). The reason for this may be that PA influences the elimination of SDZ in slow-acetylation rabbits.     

Epigenetics of the Depressed Brain: Role of Histone Acetylation and Methylation

Major depressive disorder is a chronic, remitting syndrome involving widely distributed circuits in the brain. Stable alterations in gene expression that contribute to structural and functional changes in multiple brain regions are implicated in the heterogeneity and pathogenesis of the illness. Epigenetic events that alter chromatin structure to regulate programs of gene expression have been associated with depression-related behavior, antidepressant action, and resistance to depression or ‘resilience'' in animal models, with increasing evidence for similar mechanisms occurring in postmortem brains of depressed humans. In this review, we discuss recent advances in our understanding of epigenetic contributions to depression, in particular the role of histone acetylation and methylation, which are revealing novel mechanistic insight into the syndrome that may aid in the development of novel targets for depression treatment.