Differential biotransformation of the enantiomers of isoidide dinitrate in isolated rat aorta

Previous studies have demonstrated that the D-enantiomer of isoidide dinitrate (IIDN) is 10-fold more potent than the L-enantiomer for relaxation and cyclic GMP accumulation in isolated rat aorta. To test whether preferential biotransformation of D-IIDN to a species that activates guanylate cyclase is the basis for this observed enantioselectivity, paired segments of rat aorta were exposed to D- and L-IIDN and the tissue accumulation of the parent compound and the formation of their respective metabolites (D- and L-isoidide mononitrate, IIMN) were determined. The extent of relaxation of rat aorta following exposure to 2 microM D-IIDN was greater than that by L-IIDN over a 5-minute time course, and this was associated with a higher rate of D-IIDN biotransformation to D-IIMN at all time points. In addition, the rate of D-IIDN biotransformation was greater than that of L-IIDN at most IIDN concentrations tested. By contrast, the amount of D- and L-IIDN in the tissue was the same at all time points and concentrations tested, indicating that selective uptake of D-IIDN into blood vessels did not occur. When tissues were made tolerant to organic nitrate-induced relaxation by treatment with a high concentration of glyceryl trinitrate, the biotransformation of both D- and L-IIDN was attenuated. This suggests that mechanism-based biotransformation may be affected during tolerance development. Furthermore, the association of preferential D-IIDN biotransformation with its greater potency for vasodilation and cyclic GMP accumulation suggests than an enantioselective site for biotransformation is an important component of organic nitrate-induced vasodilation.     

肌注和口服恩诺沙星在大菱鲆体内的药代动力学比较

在水温(16±0.6)℃条件下, 以20 mg/kg剂量给健康大菱鲆静注、肌注和口服恩诺沙星后, 用高效液相色谱法测定药物浓度,采用DAS2.0药动学软件对血药浓度进行分析,比较了肌注和口服两种给药方式下恩诺沙星在大菱鲆(Scophthalmus maximus)体内的药代动力学差异。结果显示,肌注和口服恩诺沙星后,在大菱鲆体内的代谢过程均符合一级吸收二室开放模型, 表达方程为C肌注=10.237e-0.702t+6.151e-0.01t-16.388e-25.796t和C口服=3.701e-0.072t+3.534e-0.007t-7.235e-0.364t。与口服给药后药代动力学参数比较, 肌注给药后的t1/2Ka(0.027h)、tmax(0.5h)、t1/2α(0.987h)和t1/2β(68.003h)均小于口服给药(1.904h、4h、9.621h和99.137h),且Cmax(21.7172μg/mL)和F(88.57%)均大于口服给药(5.3594μg/mL、66.42%)。结果表明, 肌注恩诺沙星在大菱鲆体内的吸收、消除均快于口服给药, 且比口服给药吸收完全。在试验条件下, 最佳给药方案为:肌注给药, 按鱼体重每次给药19.05 mg/kg,2天一次, 建议连续给药2-3次;口服给药,按鱼体重每次给药13.92mg/kg,1天一次, 建议连续给药3-5次, 建议休药期分别不低于30d和45d。       

Role of plasma albumin in renal elimination of a mercapturic acid. Analyses in normal and mutant analbuminemic rats

Biosynthesis of N-acetylcysteine S-conjugates of xenobiotics (mercapturic acids) occurs via interorgan metabolism and the renal transtubular transport system plays an important role in elimination of the final metabolites from the organism. To assess the behavior of a mercapturic acid in the circulation, plasma clearance of radioactive S-benzyl-N-acetylcysteine and its interaction with plasma proteins were studied in normal and mutant analbuminemic rats (NAR). Intravenously injected S-benzyl-N-acetylcysteine rapidly disappeared from the circulation both in NAR and normal animals. However, its plasma clearance was significantly higher in NAR (45.7 ml kg-1 min-1) than in normal rats (25.2 ml kg-1 min-1). Ultrafiltration analysis revealed that 18.4% and 80.1% of the mercapturate bound to plasma protein(s) from NAR and normal rats, respectively, at 50 microM ligand concentration. The mercapturic acid bound to plasma albumin with an association constant of 2.24 X 10(5) M-1 and the number of binding sites was 1.18/mol albumin. The binding was competitively inhibited by probenecid and L-tryptophan. Concomitant administration of this mercapturic acid with equimolar amounts of albumin resulted in a marked decrease in the plasma clearance (26.2 ml kg-1 min-1) and an increase in the urinary secretion of this ligand in NAR. 30 min after injection of the mercapturic acid (10 mumol/kg body weight), 27.3% and 60.4% of the injected dose was recovered from urine and kidneys of NAR and normal rats respectively. About 41% of the dose was recovered in NAR urine when the ligand was injected bound to an equimolar amount of albumin. These results suggested that albumin is important for the renal accumulation and urinary elimination of the circulating mercapturic acid.     

Des-enkephalin-gamma-endorphin: bioavailability in rats following the subcutaneous and intramuscular route of administration

A pharmacokinetic study with [3H]des-enkephalin-gamma-endorphin (3H-DE gamma E) was performed in rats after the intravenous, subcutaneous and intramuscular route of administration. Disappearance of non-metabolized 3H-DE gamma E from blood upon intravenous dosing followed a biphasic decay with half-lives of 0.7 +/- 0.3 (+/- S.D.) min for the initial distribution phase and 6.3 +/- 2.7 min for the terminal elimination phase. The central and peripheral volumes of distribution were strikingly high (0.38 and 0.55 1 X kg-1, respectively). Extensive metabolism occurred already within the first minutes after injection. The blood clearance rate was found to be 0.29 +/- 0.12 1 X min-1 X kg-1, which value points to remarkable extrahepatic elimination of the neuropeptide. As compared to the intravenous route of administration, subcutaneous or intramuscular injection of 3H-DE gamma E resulted in low but longer-lasting peptide levels in blood. These levels reached already peak values at 2 min after both routes of administration and then declined to below the limit of detection at 2-3 h. The absolute bioavailability of DE gamma E after subcutaneous injection amounted to 30.9 +/- 16.3% (range 16.0-46.9%), whereas the bioavailability after intramuscular injection was observed to be 3.5 times lower (8.5 +/- 3.0%; range 4.6-12.0%). These data suggest that subcutaneous dosing of DE gamma E might be more effective in displaying CNS activity than the intramuscular route.     

Pharmacokinetic profile of (+/-)-gossypol in male Sprague-Dawley rats following single intravenous and oral and subchronic oral administration

The pharmacokinetic profile of (+/-)-gossypol was determined in male Sprague-Dawley rats following a single intravenous or oral 10 mg/kg dose and after receiving a daily oral 10 mg/kg dose for 14 days. The intravenous plasma (+/-)-gossypol level data were fitted with a three-compartment, open-model system. The apparent half-life of elimination of (+/-)-gossypol following intravenous administration was 11.44 hr, corresponding to an elimination rate constant of 0.05 hr-1. The total plasma clearance (Cl), volume of distribution (Vd), and AUCplasma following a single intravenous administration were 0.16 liter/hr/kg, 0.05 liter/kg, and 63.09 mg.hr/liter, respectively. The bioavailability of a single oral dose of (+/-)-gossypol in rats was 60%. The change in plasma (+/-)-gossypol concentration after a single or after multiple doses showed a biphasic pattern. A single oral dose of (+/-)-gossypol, however, was eliminated five times faster than the daily administered chemical. Thus, a single oral dose of (+/-)-gossypol was eliminated at a rate constant of 0.01 hr-1, corresponding to half-life of 64.76 hr. Subchronic oral administration of (+/-)-gossypol showed an apparent half-life of 101.91 hr-1, corresponding to a rate constant of 0.007 hr-1. The results indicate that multiple oral dosing of (+/-)-gossypol resulted in its longer retention in body tissue than a single oral dose. This study suggests that pharmacokinetics of (+/-)-gossypol may play, at least in part, a role in the reproductive toxicity of subchronic but not single oral dosing.     

The pharmacokinetics and tissue distribution of sinomenine in rats and its protein binding ability in vitro

Sinomenine, an alkaloid derived from the Chinese medical plant Sinomenium acutum, was studied with regard to its pharmacokinetics and tissue distribution in rats, and to its protein binding ability in the plasma of rats and rabbits and in the solutions of albumin and alpha-1-acid-glycoprotein. An HPLC analytical method was developed for determining sinomenine. The results demonstrated that oral administration with a single dosage at a rate of 90 mg sinomenine/kg in rats achieved about 80% bioavailability, while most of the other pharmacokinetic parameters were similar to the data from the animals treated intravenously. This indicates that oral administration of sinomenine would be appropriate in clinics. In rats, at 45 min after oral dosage, the drug was found to distribute widely in the internal organs, with tissue concentrations (from highest to lowest) in the order of kidneys, liver, lungs, spleen and heart, brain and testicles. At 90 min after dosing, the tissue concentrations in the organs were markedly decreased. The liver and kidneys manifested as the dominant organs with high tissue concentrations that might be responsible for metabolism and elimination of sinomenine. Examination of the protein binding ability showed that sinomenine with 4 microg/ml concentration in the plasma of rats and rabbits or in the albumin solution achieved a protein binding rate of more than 60%, while in the solution of alpha-1-acid-glycoprotein the rate was only about 33%. This result suggests that sinomenine might have much more potent binding ability with albumin than with alpha-1-acid-glycoprotein, resulting from its acidic property.     

Pharmacokinetic study of ellagic acid in rat after oral administration of pomegranate leaf extract

Quantification of ellagic acid, the principal bioactive component of pomegranate leaf extract, in rats plasma following oral administration of pomegranate leaf extract was achieved by using a high-performance liquid chromatographic method. The calibration curve for ellagic acid was linear (r2=0.9998) ver the concentration range 0.026-1.3 microg/ml. The intra- and inter-day assays of ellagic acid from rat plasma were less than 6.52% at concentration range from 26 to 1300 ng/ml and good overall recoveries (94.5-102.4%) were found on same concentrations. The concentration-time profile was fitted with an open two-compartment system with lag time and its max concentration of ellagic acid in plasma was 213 ng/ml only 0.55 h after oral administration extract 0.8 g/kg. The pharmacokinetic profile indicates that ellagic acid has poor absorption and rapid elimination after oral administration pomegranate leaf extract, and part of it was absorbed from stomach.     

Interindividual variability in the enantiomeric disposition of ibuprofen following the oral administration of the racemic drug to healthy volunteers

The plasma disposition of the enantiomers of ibuprofen has been investigated following the oral administration of the racemic drug (400 mg) to 24 healthy male volunteers. The plasma elimination of (R)-ibuprofen was found to be more rapid than that of the S-enantiomer [plasma half-life: (R) 2.03 h; (S) 3.05 h; 2P less than 0.001], resulting in a progressive enrichment in the plasma content of this isomer, some 64% of the total area under the plasma concentration time curves (AUC) being due to the pharmacologically active enantiomer. The influence of dose on the pharmacokinetic characteristics of the enantiomers of ibuprofen, over the range 200-800 mg, was investigated in three subjects. Examination of dose-normalized AUC values and oral clearance indicate the dose dependence of (R)-ibuprofen disposition.     

Diuretic activity of the infusion of flowers from Lavandula officinalis

The diuretic activity of an infusion of Lavandula officinalis was studied in the Wistar rat. Thus, the kinetics of hydroelectrolytic elimination in response to the oral administration of an infusion of pharmaceutical lavender flowers were measured in the rats. Experiments were completed under similar conditions using a synthetic pharmacological diuretic, Diamox. The aqueous extract of this aromatic plant accelerated the elimination of the water overload. At the peak of the diuretic response, urinary osmolarity was significantly less than that of controls (111+/-14 vs. 195+/-11 mosmol x kg(-1)). Sodium excretion was moderate following administration of the infusion when compared to the synthetic diuretic. The stability of the aldosterone concentrations in the plasma and the absence of correlation with plasma sodium concentrations, coupled with the observed clearance of the free water (0.055+/-0.007 vs. 0.045+/-0.012 mL x min(-1)) show that the increase in diuresis and the moderate increase in sodium excretion are of tubular origin. The result of the phytochemical analysis of hexane extracts in the infusion and in urine indicated that four or five chemical factors may be involved in the diuretic effect of lavender.     

达氟沙星在史氏鲟体内药物代谢动力学比较研究

采用高效液相色谱法测定以10mg/kg体重剂量静脉注射和口服给药后史氏鲟血浆中达氟沙星的浓度。该法采用C18色谱柱,流动相为乙腈-水相(15∶85),荧光激发波长和发射波长分别为280nm和450nm,样品用甲醇沉淀蛋白,离心取上清液进样。达氟沙星在0.005-1.0μg/mL范围内线性关系良好,本方法的最低检测限为0.005μg/mL。健康鱼单剂量静注达氟沙星(10mg/kg),其药时数据符合无吸收的三室开放模型,方程为C=5.830-5.582t+4.162-1.157t+0.852-0.029t,主要动力学参数如下:t1/2α0.552h;t1/2β22.186h;AUC34.226mg/(L.h);V 10.922L/kg;Vb10.144L/kg;ke 10.317h.Ah感染组的V1减小至0.290L/kg,静注感染组鱼体内达氟沙星的消除没有显著的改变。健康口服组数据结果符合一级吸收二室开放模型,血药浓度和时间方程为C=1.278e-0.073t+0.177e-0.089t-1.455e-0.329t。药动学常数分别为:t1/2ka9.491h,t1/2β78.267h,Tmax6.284h,Cmax0.791mg/mL;α0.073h。但Ah感染改变达氟沙星口服给药后在史氏鲟体内的吸收、分布和消除。分布速率常数降低为0.050/h。消除减慢,消除半哀期延长为93.988h,达峰时间延长为至9.060h,峰浓度降低为0.585mg/mL。口服达氟沙星水溶液,健康及感染组史氏鲟对达氟沙星生物利用度分别为96.503%和94.435%。本实验结果表明达氟沙星在健康史氏鲟体内分布广泛、吸收较完全。感染Ah对达氟沙星在史氏鲟体内的吸收、分布及消除规律均有不同程度的影响,其中口服给药的影响更为显著。达氟沙星可用于史氏鲟感染Ah的治疗。       

Sexual dimorphism in the renin-angiotensin system in aging spontaneously hypertensive rats

In young adult spontaneously hypertensive rats (SHR), mean arterial pressure (MAP) is higher in males than in females and inhibition of the renin-angiotensin system (RAS) eliminates this sex difference. After cessation of estrous cycling in female SHR, MAP is similar to that in male SHR. The purpose of this study was to determine the role of the RAS in maintenance of hypertension in aging male and female SHR. At 16 mo of age, MAP was similar in male and female SHR (183+/-5 vs. 193+/-8 mmHg), and chronic losartan (40 mg.kg-1.day-1 po for 3 wk) reduced MAP by 52% (to 90+/-8 mmHg, P<0.05 vs. control) in males and 37% (to 123+/-11 mmHg, P<0.05 vs. control) in females (P<0.05, females vs. males). The effect of losartan on angiotensin type 1 (AT1) receptor blockade was similar: MAP responses to acute doses of ANG II (62.5-250 ng/kg) were blocked to a similar extent in losartan-treated males and females. F2-isoprostane excretion was reduced with losartan more in males than in females. There were no sex differences in plasma renin activity, plasma angiotensinogen or ANG II, or renal expression of AT1 receptors, angiotensin-converting enzyme, or renin. However, renal angiotensinogen mRNA and protein expression was higher in old males than females, whereas renal ANG II was higher in old females than males. The data show that, in aging SHR, when blood pressures are similar, there remains a sexual dimorphism in the response to AT1 receptor antagonism, and the differences may involve sex differences in mechanisms responsible for oxidative stress with aging.     

Acute anemia results in an increased glucose dependence during sustained exercise

We evaluated whether acute anemia results in altered blood glucose utilization during sustained exercise at 26.8 m/min on 0% grade, which elicited approximately 60-70% maximal O2 consumption. Acute anemia was induced in female Sprague-Dawley rats by isovolumic plasma exchange transfusion. Hemoglobin and hematocrit were reduced 33% by exchange transfusion to 8.6 +/- 0.4 g/dl and 26.5 +/- 1%, respectively. Glucose kinetics were determined by primed continuous infusion of [6-3H]glucose. Rates of O2 consumption were similar during rest (pooled means 25.1 +/- 1.8 ml.kg-1.min-1) and exercise (pooled means 46.8 +/- 3.0 ml.kg-1.min-1). Resting blood glucose and lactate concentrations were not different in anemic animals (pooled means 5.1 +/- 0.2 and 0.9 +/- 0.02 mM, respectively). Exercise resulted in significantly decreased blood glucose (4.0 +/- 0.2 vs. 4.6 +/- 0.1 mM) and elevated lactate (6.1 +/- 0.4 vs. 2.3 +/- 0.5 mM) concentrations in anemic animals. Glucose turnover rates (Rt) were not different between anemic and control animals at rest and averaged 58.8 +/- 3.6 mumol.kg-1.min-1. Exercise resulted in a 30% greater increase in Rt in anemic (141.7 +/- 3.2 mumol.kg-1.min-1) than in control animals (111.2 +/- 5.2 mumol.kg-1.min-1). Metabolic clearance rates (MCR = Rt/[glucose]) were not different at rest (11.6 +/- 7.4) but were significantly greater in anemic (55.2 +/- 5.7 ml.kg-1.min-1) than in control animals (24.3 +/- 1.4 ml.kg-1.min-1) during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of muscarinic blockade on the thermic effect of oral or intravenous carbohydrate.

Muscarinic blockade by atropine has been shown to decrease the thermic effect of a mixed meal, but not of intravenous glucose. To further delineate the mechanisms involved in the atropine-induced inhibition of thermogenesis after a meal, plasma substrate and hormone concentrations, energy expenditure (EE) and substrate oxidation rates were measured before and during a continuous glucose infusion (44.4 mumol.kg-1.min-1) with or without atropine. After 2 h of glucose infusion, a 20-g oral fructose load was administered while the glucose infusion was continued. Plasma insulin concentrations attained a plateau at 596 (SEM 100) pmol.l-1 after 120 min of glucose infusion and were not affected by muscarinic blockade; plasma glucose concentrations peaked at 13.3 (SEM 0.5) mmol.l-1 at 90 min and decreased progressively thereafter; no difference was observed with or without atropine. Plasma free fatty acid and glucagon concentrations, with or without atropine, were both decreased to 201 (SEM 18) mumol.l-1 and 74 (SEM 4) ng.l-1, respectively, after 2 h of glucose infusion, and were not further suppressed after oral fructose. Carbohydrate oxidation rates (CHO(ox)) increased to 20.8 (SEM 1.4) mumol.kg-1.min-1 and lipid oxidation rates (Lox) decreased to 1.5 (SEM 0.3) mumol.kg-1.min-1 between 90 and 120 min after the beginning of glucose infusion and were not affected by atropine. Glucose-induced thermogenesis was similar with [6.5% (SEM 1.4%) of basal EE] or without [6.0% (SEM 1.0%), NS) muscarinic blockade during the 30 min preceding fructose ingestion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacokinetics of propetamphos following intravenous administration in the F344 rat

Propetamphos [(E)-l-methylethyl 3[[(ethylamino)methoxyphosphinothioyl]oxy]-2-bu-tenoate], the active ingredient in Safrotin,® is an organophosphate developed by Sandoz, Ltd.® (Switzerland) as an insecticide (1). Although metabolism of propetamphos has been previously investigated (2,3), there is no pharmacokinetic data available in the literature. The current studies were undertaken to investigate the pharmacokinetics of propetamphos following intravenous administration in male and female Fischer 344 (F344) rats. Rats were dosed via an indwelling jugular cannula at a dose of 12 mg/kg (one-tenth the oral LD-50). Blood samples were withdrawn via the cannula at predetermined timepoints to quantitate plasma concentrations of propetamphos over time. Propetamphos is highly bound to plasma proteins (free fraction = 0.06). Free propetamphos concentration in plasma vs. time data were analyzed by noncompartmental methods. The terminal elimination rate constant, λ, was significantly different for males versus females (0.015 min^?1 for males and 0.037 min^?1 for females, p = 0.001). Plasma was cleared of unbound propetamphos at rates of 0.559 ± 0.069 and 0.828 ± 0.181 L/min/kg for males and females (mean ± standard error). Mean residence times (MRTs) for propetamphos in the body for males and females were 28.3 ± 5.7 and 14.4 ± 3.5 min, and the volume of distribution at steady state (Vss) was 14.7 ± 2.6 and 12.3 ± 4.5 L/kg. The differences in these parameters, clearance (CI), MRT, and Vss, were not statistically significant at the p < 0.05 level for males versus females, but MRT was nearly significantly different (p = 0.08). Because of the rapid elimination of propetamphos from plasma following intravenous administration, it is unlikely that propetamphos would bioaccumulate in environmentally exposed animals. Although the pharmacokinetic parameters were not statistically different for males and females in these studies, there was a clear clinical difference in their susceptibility to propetamphos toxicity. Female rats presented with overt signs of organophosphate intoxication, whereas males were only slightly effected. The observed gender-related clinical difference in susceptibility to toxicity suggests that there may be a difference in the extent of elimination due to activation versus detoxication of propetamphos in males and females. Another possible explanation for the clinical difference in propetamphos toxicity is that inhibition of acetyl-cholinesterase by the activated, oxygenated form of propetamphos (propetamphos oxon) may be greater in females than in males.     

Absorption and enterohepatic circulation of baicalin in rats

Pharmacokinetics of baicalin, in form of its parent drug (BG) and conjugated metabolites (BGM), were studied following intravenous and oral administration of baicalin to intact rats. The enterohepatic circulation of BG and BGM was also assessed in a linked-rat model. Multiple plasma and urine samples were collected, and concentrations of BG and BGM were determined using a liquid chromatography/tandem mass spectrometry method. The concentration of BGM was assayed in the form of baicalein after treatment with beta-glucuronidase/sulfatase. After i.v. administration, plasma concentration of BG rapidly declined with the elimination half-life (T1/2) of 0.1 till 4 h post dose, followed by slight increase from 4-8 h in plasma concentrations after drug administration. These plasma concentrations resulted in a significant prolongation of the terminal elimination half-life of BG (T1/2 TER, 9.7 h). BG also displayed slight increase in plasma concentrations (12-24 h) after oral administration, with T1/2 TER of 12.1 h. Based on the AUC of BG and BGM, the absolute bioavailability of baicalin was 2.2+/-0.2% and 27.8+/-5.6%, respectively. The exposure of baicalin to the systemic circulation was approximately 118-fold lower than that of BGM after oral administration (AUC0-t, 4.43 versus 523.97 nmol.h/mL). The high extent of glucuronidation suggested the possible presence of enterohepatic circulation, which was confirmed in the linked-rat model since plasma concentrations of BG and BGM were observed in bile-recipient rats at 4 to 36 h. The extent of enterohepatic circulation after intravenous administration of baicalin was 4.8% and 13.3% for BG and BGM, respectively. It was determined that 18.7% and 19.3% of the administered baicalin were subjected to enterohepatic circulation for BG and BGM, respectively, after oral administration. These results confirm that BG undergoes extensive first-pass glucuronidation and that enterohepatic circulation contributes significantly to the exposure of BG and BGM in rats.     

Athletes'' pseudoanaemia

To characterize the so-called pseudoanaemia of endurance-trained athletes, the plasma volume (PV), red cell volume (RCV) and total blood volume (TBV) of 12 male and 12 female athletes and 5 male and 5 female nonexercising controls were measured using 125I-labelled human serum albumin and 51Cr-labelled erythrocytes. The mean PV of the male athletes (52.8 ml.kg-1) was 37.5% higher than that of the controls (38.4 ml.kg-1), while the 18.1% increase measured in the female runners (51.5 ml.kg-1) over the controls (43.6 ml.kg-1) was a novel observation. Although the RCV was significantly greater (34.7%) in male athletes (32.6 ml.kg-1 vs 24.2 ml.kg-1 in the controls), a similar elevation (3.6%) was not found in the female athletes (25.9 ml.kg-1) compared to the sedentary women (22.8 ml.kg-1). This could have been due to iron-limited erythropoiesis because the RCV of the female athletes defined as clinically anaemic was markedly lower that of the nonanaemic women (P less than 0.05). The elevated plasma protein mass and concentration measured in the athletes partly accounted for their expanded PV. It was concluded that the decreased blood haemoglobin levels reported in the endurance athletes was largely a dilutional effect.     

Mouse erythrocytes as carriers for coencapsulated alcohol and aldehyde dehydrogenase obtained by electroporation in vivo survival rate in circulation, organ distribution and ethanol degradation

Alcohol dehydrogenase and aldehyde dehydrogenase (ADH and ALDH) have been coencapsulated into mouse erythrocytes by an electroporation technique. The optimal conditions were achieved as follows: 420 V, four pulses of 1 ms every 15 min. at 37 degrees C, completed by resealing: 1 h at 37 degrees C. An encapsulation yield ranging from 11-12% was obtained for ADH+ALDH-loaded erythrocytes. Carrier cell recovery was 52%. Electroporated-RBCs observed under Scanning electron microscopy exhibited a tendency toward invaginated sphero-stomatocytes. These invaginations were not found in electroporated/resealed RBCs. The intravenous administration of 51Cr-RBCs manifested a bimodal pharmacokinetic profile: an initial phase (t1/2alpha) with a rapid decrease of plasma 51Cr-RBCs followed by a slow and prolonged elimination phase (t1/2beta). The values corresponding to in vivo survival rate during the elimination phase indicated that the survival rate of 51Cr-electroporated loaded-RBCs was slightly lower (t1/2beta, 4.5 days) than 51Cr-native RBCs (t1/2beta, 5.3 days). The mean clearance values from blood of electroporated 51Cr-RBCs (unloaded and loaded) were higher (0.51 %51Cr/day and 0.54 %51Cr/day, respectively) than the obtained for native 51Cr-RBCs (0.18 %51Cr/day). The target organs for electroporated RBCs proved to be the same as for native RBCs. However, electroporated RBCs showed highest accumulation in liver, spleen and lung, since they were promptly recognized by the reticuloendothelium system. Mice induced to the state of acute ethanol intoxication and treated with ADH+ALDH-RBCs clearly showed a lower level of ethanol concentration in plasma (less than 43% ethanol) than the intoxicated mice treated with native RBCs. En consequence the clearance values of ethanol from blood in intoxicated mice treated with ADH+ALDH-RBCs (0.39 ml/min) were higher than the treated with native RBCs (0.20 ml/min). The results obtained suggest that ADH+ALDH-loaded erythrocytes could be used as a potential carrier system for in vivo removal of high levels of ethanol from blood caused by excessive alcohol consumption.     

Simultaneous determination of catechin, epicatechin and epicatechin gallate in rat plasma by LC-ESI-MS/MS for pharmacokinetic studies after oral administration of Cynomorium songaricum extract

A rapid and valid method was developed for simultaneous determination catechin, epicatechin and epicatechin gallate in rat plasmas using scopoletin (103 ng mL(-1)) as an internal standard (IS). The separation was performed on Eclipse plus C18 column (100 mm × 4.6 mm, 1.8 μm) at a flow rate of 0.3 mL min(-1), and acetonitrile-0.1% formic acid was used as mobile phase. The recoveries of three analytes and IS were more than 78.9%. The lower limits of quantitation (LLOQ) in rat plasma were 2.14, 2.38 and 2.08 ng mL(-1) respectively for catechin, epicatechin and epicatechin gallate. Intra-day and inter-day precisions were within 12%. The accuracies were more than 85%. After single oral administration of 15.25 g kg(-1) Cynomorium songaricum extract, C(max) of catechin, epicatechin and epicatechin gallate in rat plasma were respectively 86.69±38.65, 32.57±15.00 and 36.93±12.62 ng mL(-1) while T(max) values were respectively 0.15±0.09, 0.20±0.10 and 0.20±0.13 h. The results demonstrated that the present LC-MS/MS method was sensitive enough for pharmacokinetic study of catichins following oral administration of C. songaricum extract.     

Determination of tenatoprazole enantiomers and their enantioselective pharmacokinetics in rats

The enantioselective pharmacokinetics of tenatoprazole were studied in Wistar rats after the administration of a single oral dose of rac-tenatoprazole. Serial plasma samples were collected; and the pharmacokinetic behavior of each enantiomer was characterized using a sequential achiral and chiral liquid chromatographic method. Tenatoprazole was extracted from a small aliquot of plasma (100 microl) by one-step extraction using hexane-dichloromethane-isopropanol (20:10:1, v/v/v) as extract solvent. Plasma drug concentration-time data were analyzed for each enantiomer by using a noncompartmental method. The AUC(0-infinity) and C(max) values of (+)-tenatoprazole were significantly greater than those of (-)-tenatoprazole (P < 0.001). The mean AUC(0-infinity) value of (+)-tenatoprazole was 7.5 times greater than that of (-)-tenatoprazole after oral administration of rac-tenatoprazole to rats at a dose of 5 mg/kg. There are also significant differences in t(1/2) and CL/F (P < 0.01 and P < 0.001, respectively) values between enantiomers. This study suggests that the pharmacokinetics of tenatoprazole are enantioselective in rats.     

Route-dependent stereoselective pharmacokinetics of tramadol and its active O-demethylated metabolite in rats

The effects of route of administration on the stereoselective pharmacokinetics of tramadol (T) and its active metabolite (M1) were studied in rats. A single 20 mg/kg dose of racemic T was administered through intravenous, intraperitoneal, or oral route to different groups of rats, and blood and urine samples were collected. Samples were analyzed using chiral chromatography, and pharmacokinetic parameters (mean +/- SD) were estimated by noncompartmental methods. Following intravenous injection, there was no stereoselectivity in the pharmacokinetics of T. Both enantiomers showed clearance values (62.5 +/- 27.2 and 64.4 +/- 39.0 ml/min/kg for (+)- and (-)-T, respectively) that were equal or higher than the reported liver blood flow in rats. Similar to T, the area under the plasma concentration-time curves (AUCs) of M1 did not exhibit stereoselectivity after intravenous administration of the parent drug. However, the systemic availability of (+)-T was significantly (P < 0.05) higher than that of its antipode following intraperitoneal (0.527 +/- 0.240 vs. 0.373 +/- 0.189) and oral (0.307 +/- 0.136 vs. 0.159 +/- 0.115) administrations. The AUC of the M1 enantiomers, on the other hand, remained mostly nonstereoselective regardless of the route of administration. Pharmacokinetic analysis indicated that the stereoselectivity in the pharmacokinetics of oral T is due to stereoselective first pass metabolism in the liver and, possibly, in the gastrointestinal tract. The direction and extent of stereoselectivity in the pharmacokinetics of T and M1 in rats were in agreement with those previously reported in humans, suggesting that the rat may be a suitable model for enantioselective studies of T pharmacokinetics.