Biomedical subjects

T Iga

Publications and source records attributed to T Iga.

At least 127 records · Page 7Linked to original sources

PubMed1994

Stereospecific distribution of methylphenidate enantiomers in rat brain: specific binding to dopamine reuptake sites.

To investigate the stereoselective distribution of methylphenidate (MPD) enantiomers in rats, the concentrations of each enantiomer were determined in plasma and brain regions (cerebellum, striatum, basal forebrain, brain stem, and cortex) after iv administration of racemic MPD and its individual enantiomers. The concentrations of MPD enantiomers in each brain region reached pseudo-steady state within 10 min after iv administration of racemic MPD (2 mg/kg dose). The influx clearances for MPD calculated from Kpapp values in each brain region were not significantly different between MPD enantiomers and between the five brain regions. The mean Kpapp values for (+)-MPD in the striatum at 120 and 240 min after administration of racemic MPD were 10.1 and 10.5, respectively, and these values at each time were significantly larger than the Kpapp values (7.5 and 7.0, respectively) for the (-)-isomer (P < 0.01). The Kpapp value for (+)-MPD in the striatum decreased by coadministration of mazindol as an inhibition of both dopamine and norepinephrine reuptake, but it was not changed by desipramine as a norepinephrine reuptake inhibitor. These results suggest that (+)-MPD was bound specifically to the dopamine reuptake site in the striatum.

Animals↗

PubMed1994

Effect of renal or hepatic dysfunction on neurotoxic convulsion induced by ranitidine in mice.

We investigated the effect of acute renal and hepatic dysfunction on the neurotoxicity of ranitidine, a histamine H2 receptor antagonist. Experimental acute hepatic and renal dysfunction in mice were produced by i.p. injection of uranyl nitrate (UN) and carbon tetrachloride (CT), respectively. Ranitidine was then constantly infused into the tail vein until the onset of clonic convulsion. When compared to control mice, UN treated mice had a significantly shorter onset time to clonic convulsion, lower total dose and higher plasma concentration at initiation of clonic convulsion. In contrast, the convulsive threshold concentration in the brain of UN treated mice was not significantly different from that of control mice. In CT treated mice, all pharmacokinetic and pharmacodynamic data described above were not significantly different from those of the control mice. No significant difference in the brain/plasma concentration ratio was observed between both disease models and the corresponding control mice. Finally, the effect of UN and CT treatment on the convulsive potency after intracerebral (i.c.) administration of ranitidine was investigated in mice. Potentiation of the intrinsic neurotoxic sensitivity to ranitidine could not be demonstrated for mice with renal or hepatic dysfunction. From these findings, we conclude that renal dysfunction is a risk factor for ranitidine neurotoxicity, and this increased risk results from increase in the drug concentration in plasma and brain as a result of impaired renal excretion. No apparent effect of acute hepatic dysfunction was observed on both the pharmacokinetic and pharmacodynamic behavior of the drug.

Acute Disease↗

PubMed1994

Pharmacokinetics and pharmacodynamics of (+)-threo-methylphenidate enantiomer in patients with hypersomnia.

The pharmacokinetics of (+)-methylphenidate after oral administration of 20 mg racemic methylphenidate hydrochloride and the relationship between clinical effects of plasma (+)-methylphenidate concentration were investigated in 15 patients with hypersomnia and four healthy volunteers. The elimination half-life of (+)-methylphenidate in patients was within the range of 2.6 to 3 hours, and the time to reach the peak concentration ranged from 1 to 3 hours. The values of half-life and time to reach the peak concentration in the patients were almost the same as the values in healthy subjects. The plasma (+)-methylphenidate concentration profiles after repeated administration of racemic methylphenidate were similar to those after single administration. No correlation was observed between the plasma (+)-methylphenidate concentration and the subjective sleepiness as measured by Stanford Sleepiness Scale. On the other hand, a significant correlation was found between the sleep latency as measured by the multiple sleep latency test and the plasma concentrations of (+)-methylphenidate (r = 0.850). The time course of the sleep latency after repeated administration was similar to that after single administration. The sleep latency of more than 10 minutes was achieved by maintaining the plasma (+)-methylphenidate concentrations above 3 ng/ml.

Administration, Oral↗

PubMed1994

Decreased cyclosporin A absorption after treatment with GoLytely lavage solution in rats.

Recently we observed a case in which the cyclosporin A absorption decreased after treatment with GoLytely lavage solution in a kidney transplant patient. In this study, we confirmed the decrease of the blood concentration of cyclosporin A after oral administration by GoLytely (Macrogol 3350) based on experiments with rats. The peak blood cyclosporin A concentration, and the area under the blood drug concentration-time curve from 0 to 24 h in the GoLytely-administered group were significantly lower than the control group. In the case of gastrointestinal dysfunction such as diarrhoea, or in treatment with laxatives such as GoLytely lavage solution, whole blood cyclosporin levels must be carefully monitored, and intravenous cyclosporin A may be more suitable for providing adequate immunosuppression.

Analysis of Variance↗

PubMed1994

Appearance of tolerance in the increase of contractile muscle tension by ambenonium in rats.

The relationship between the concentration of ambenonium (AMB), a selective and reversible acetylcholinesterase (AChE) inhibitor, in plasma and the potentiation of contractile muscle tension was investigated using a sciatic nerve-muscle preparation of rat. The developed isometric contraction was enhanced dose-dependently after i.v. administration of low doses (5-20 nmol/kg) of AMB, but the contraction was weakened when AMB was administered at high doses (100-1000 nmol/kg), and the concentration-effect relationship was bell-shaped. The muscle contraction profile after 50 nmol/kg administration without previous administration, with 20 nmol/kg and with 50 nmol/kg administered previously were quite different from each other. These findings suggest that the potentiation of contractile muscle tension by AMB may be acutely tolerated and the concentration-effect relationship may change time-dependently.

Ambenonium Chloride↗

PubMed1993

Pharmacokinetic profiles of glycyrrhizin in patients with chronic hepatitis.

The pharmacokinetics of glycyrrhizin (G) in eight patients with chronic hepatitis receiving chronically i.v. administration of 120 mg dose of G was investigated. The plasma concentration of G in the patients after dosing declined in a monophasic manner. However, the pharmacokinetic profiles varied among patients. The mean elimination half-life (t1/2) and the total body clearance (CLtot) were 6.0 h (range 4.3-10.7 h) and 7.9 ml h-1 kg-1 (4.5-12.7 ml h-1 kg-1), respectively. The variation of the CLtot for G was closely related to that of aspartate aminotransferase (r = -0.739, p < 0.05) and alanine aminotransferase (r = -0.783, p < 0.05) activities in the plasma.

Adult↗

PubMed1993

Kinetic analysis of glycyrrhetic acid, an active metabolite of glycyrrhizin, in rats: role of enterohepatic circulation.

The role of enterohepatic circulation of glycyrrhetic acid (GA) in rats was determined by kinetic analysis of GA. The concentrations of GA in the plasma of the control rat (without bile duct cannulation) during the first 5 h after intravenous (iv) administration of GA (2, 5, 10, and 20 mg/kg) were similar to those in the bile duct-cannulated rat at each dose. No significant difference was observed in the values of the terminal half-life, the total body clearance, the distribution volume at steady state, the area under the curve of concentration in plasma versus time, and the mean residence time in each dose between both groups. When GA (2, 5, 10, and 20 mg/kg) was administered i.v. to the bile duct-cannulated rat, excretion of unchanged GA in bile was < 1% of each dose, that of the acid-hydrolyzed products was 14-16%, and that of GA-3-O-glucuronide was only 1-2%. In the control rat, a secondary peak of GA concentration was observed 12 h after i.v. administration of GA (20 mg/kg). The enterohepatic circulation of GA was confirmed by the linked-rat method in which bile of the donor rat after i.v. administration of GA (20 mg/kg) was allowed to flow directly into the duodenum of the recipient rat. GA was found in the plasma of the recipient rat after 6 h, and its concentration reached the maximum (approximately 0.5 microgram/mL) 8-12 h after dosing the donor rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Nonlinear kinetics of threo-methylphenidate enantiomers in a patient with narcolepsy and in healthy volunteers.

We have studied the pharmacokinetics of methylphenidate enantiomers after the oral administration of different doses of racemic methylphenidate to one patient with narcolepsy and to four healthy volunteers. The plasma concentrations of (+)-methylphenidate were much higher than those of (-)-methylphenidate after each dose in all subjects. In the patient the oral clearance (CL/f) of (+)-methylphenidate fell 3-fold and the area under the concentration-time curve (AUC) rose 7-fold when the dose was increased from 20 to 40 mg (from 0.27 to 0.53 mg.kg-1), in spite of the relatively constant terminal half-life of 2.6-2.7 h. Similar dose-dependency was also observed in the healthy volunteers in the dose range of 10-60 mg (0.12-0.77 mg.kg-1). The mean value of CL/f for the 40 mg dose was significantly lower than that for the 20 mg dose. The mean AUC of the (+)-isomer corrected to a dose of 10 mg increased significantly between the 20 mg and 40 mg doses. In the urine (+)- and (-)-ritalinic acid were excreted for 48 h after each dose as 32-37% and 34-40% of the dose respectively. The mean total recoveries (sum of enantiomers of methylphenidate and its metabolite, ritalinic acid) in the urine were relatively constant (63-78% of the doses), suggesting that the changes in AUC with dose may not be due to a change in the intestinal absorption of racemic methylphenidate. We conclude that the nonlinear kinetics of (+)-methylphenidate may be due to saturation of its presystemic elimination.

Administration, Oral↗

PubMed1993

Prediction of the therapeutic dose for beta-stimulants based on preclinical data: application of oral dosage forms and aerosols to asthmatic patients.

The therapeutic doses of beta-stimulants in the treatment of bronchial asthma show wide variation among the drugs. In the present study, we tried to construct a system for prediction of the optimum clinical dose of beta-stimulants as oral dosage forms and aerosols using the data from preclinical pharmacological studies and pharmacokinetic data in humans. Values of EC50 (drug concentration that gives the half-maximum bronchodilator effect) in the in vitro studies based on isolated trachea of guinea pigs were collected from the literature. The ratios of the EC50 value of each drug to that of isoproterenol were used as the indicator of in vitro pharmacological activity. There were significant correlations between the EC50 ratios and the oral dose or the maximum plasma concentration after single oral administration, but the correlation coefficients were relatively small (r < .9). On the other hand, a linear log-log relationship was observed between the EC50 ratio and the maximum plasma unbound concentration (Cu(max)) (slope = 0.907, r = .955, p < 0.001). In the case of aerosols, a good correlation was observed between the EC50 ratio and the dose (slope = 0.770, r = .900, p < 0.01). The predicted concentration of beta-stimulants in the lung after aerosol administration tended to be higher than the Cu(max) after oral administration, suggesting the contribution of nonspecific binding in the lung tissue. These findings indicate the possibility of predicting the appropriate dose of beta-stimulants based on the preclinical pharmacological data and the pharmacokinetic data in humans.

Administration, Oral↗

PubMed1993

Classification of benzodiazepine hypnotics in humans based on receptor occupancy theory.

Benzodiazepine (BZP) hypnotics are now classified into four groups according to their plasma elimination rates: ultrashort-, short-, intermediate-, and long-acting drugs. Since the specific binding affinities for the BZP receptor vary widely among the BZPs and their active metabolites, it may be more reasonable to correlate their pharmacological activities with the BZP receptor occupancy rather than with their plasma concentrations. The time courses of total plasma concentrations of BZPs and their active metabolites after a single oral administration were obtained from the literature, and their unbound concentrations (Cu) were calculated from the reported values of their plasma unbound fractions. The data of the receptor binding affinities of the BZPs, reported as dissociation constants (Kd) determined by in vitro binding experiments, were also obtained from the literature. Using these values, the time courses of receptor occupancies [Cu/(Kd + Cu) x 100%] were calculated for the various BZPs. A mutual competitive inhibition was considered in the case of the drugs that had active metabolites. Although plasma total and unbound concentration time profiles of the BZPs showed a wide variation, similar patterns were obtained for the time courses of the receptor occupancy among the BZPs in each group, indicating that the BZP hypnotics can be classified more conveniently based on receptor occupancy theory.

Animals↗

PubMed1993

Comparison of the hepatic uptake clearances of fifteen drugs with a wide range of membrane permeabilities in isolated rat hepatocytes and perfused rat livers.

The hepatic uptake clearances of 15 ligands with a wide range of permeabilities were determined in rats using two techniques: centrifugal filtration with isolated hepatocytes and the multiple indicator dilution (MID) method with isolated perfused livers. Some of the uptake clearance values were taken from the literature. Uptake clearance values obtained from isolated hepatocytes were extrapolated to that per gram liver (PSinf.cell), assuming that 1 g of liver has 1.3 x 10(8) cells. The values of PSinf.cell varied from approximately 0.1 to 72 (mL/min/g liver). The values of PSinf.cell were similar to those (PSinf.MID) determined by the MID method for ligands with uptake clearances below approximately 1 mL/min/g liver. However, for the ligands with larger uptake clearances, the PSinf.MID values were lower than the PSinf.cell values and appeared to reach an upper limit (approx. 15-20 mL/min/g liver). The PSinf.cell values of 1-propranolol, tetraphenylphosphonium (TPP+), and diazepam were 72, 43, and 22 mL/min/g liver, respectively, whereas their uptake clearances (PSinf.MID) determined by the MID method were 4 to 10 times lower. One of the possible mechanisms for this discrepancy is that an unstirred water layer, which may exist in Disse's space in isolated perfused livers (and probably under in vivo condition), limits the hepatic uptake rate of ligands with extremely high membrane permeabilities.

Animals↗

PubMed1993

Dose-dependent hepatic handling of l-propranolol determined by multiple indicator dilution method: influence of tissue binding of l-propranolol on its hepatic elimination.

Concentration-dependency in the hepatic elimination of l-propranolol (l-PR) was investigated over a wide range of concentrations from 60 to 2200 microM in an isolated rat liver perfusion system. Under the steady-state condition produced by unlabeled l-PR at various concentrations, 3H-l-PR and 14C-inulin were bolusly injected into the portal vein, and the outflow was collected at 0.5 s intervals over 30 s. Up to 300 microM, the instantaneous hepatic availability of l-PR was approximately 4%, while it abruptly increased when the perfusate concentration exceeded 300 microM. To determine which process (influx or efflux or sequestration process) caused the nonlinearity, we calculated the rate constants k1 (influx), k2 (efflux), and k3 (sequestration) based on the "distributed" model. With increasing l-PR concentration in the perfusate, k2 increased approximately two times, whereas k3 decreased to approximately one-half. In contrast, k1 was independent of the perfusate concentration. The concentration-dependency of k2 was explained by saturation of l-PR tissue binding, since the tissue unbound fraction of l-PR obtained with liver homogenates and isolated hepatocytes increased approximately two times. The efflux and sequestration clearances were then normalized by the unbound fractions in the liver. The efflux clearance for unbound l-PR was constant irrespective of the perfusate concentration, whereas the sequestration clearance for unbound l-PR (CL(int) showed Michaelis-Menten type saturation (Km = 28 microM, Vmax = 2.8 mumol/min/g liver, alpha (nonspecific) = 2- ml/min/g liver).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Prediction of therapeutic doses of beta-adrenergic receptor blocking agents based on quantitative structure-pharmacokinetic/pharmacodynamic relationship.

The usual therapeutic doses for the treatment of both angina pectoris and cardiac arrhythmia vary widely among beta-blocking agents, with a maximum of about a 200-fold difference, despite subjects' same clinical improvement at the varying doses. In order to clarify the mechanism of this difference, we analyzed retrospectively the cardiac pharmacological activities of beta-blocking agents based on the receptor occupancy theory by using both their unbound concentrations in plasma at steady state (Cssf), as well as dissociation constants (KB and KI, which were determined by in vitro binding experiments and by in vitro pharmacological experiments, respectively) for a beta 1 receptor. A significant log-linear relationship between Cssf and the KB values was obtained with a slope of regression line of 0.91 (r = 0.83, p < 0.01). On the other hand, the correlation coefficient of the relationship between Cssf and the KI values was low, with a slope of about 0.5 (r = 0.80, p < 0.01). The beta 1 receptor occupancies calculated from KB values at the steady state condition after the oral administration of usual doses were almost constant (80.5 +/- 16.8%), regardless of the wide variation of usual doses of the drugs. This result indicated that the receptor occupancy may be an appropriate indicator for the pharmacological activity of the drug. Furthermore, there were significant relationships between the primary pharmacokinetic parameters: Cb/Cf, CLtot/F, and Vdssf, and the octanol/water partition coefficient (PC), with correlation coefficients of 0.80, 0.50 and 0.85, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗

PubMed1993

Sensitive determination of ambenonium in plasma using inhibitory activity to acetylcholinesterase.

A sensitive analytical method for the determination of ambenonium, a selective acetylcholinesterase inhibitor, in plasma was developed. The procedure involves ultrafiltration to remove endogenous plasma cholinesterase, followed by colorimetric measurement of the inhibitory activity to acetylcholinesterase by the thiocholine method. Coefficient of variation of within-day triplicate analysis is less than 20% at the concentration of 5 nM. Detection limit of this method is 1 nM, which is twice lower than the most sensitive HPLC method reported previously. This assay procedure is applied to the pharmacokinetic study of ambenonium after intravenous administration of low dose (10-20 nmol/kg) to rat. This new method is rapid and simple and makes it possible to determine the ambenonium concentration in plasma with good accuracy.

Acetylcholinesterase↗

PubMed1993

Inhibition of GABAA receptor-mediated current responses by enoxacin (new quinolone) and felbinac (non-steroidal anti-inflammatory drug) in Xenopus oocytes injected with mouse-brain messenger RNA.

The convulsant interaction between enoxacin (ENX), a new quinolone antibacterial agent (NQ), and felbinac (FLB), a non-steroidal anti-inflammatory drug (NSAID), in vivo was reproduced as the change of GABA-induced current response in Xenopus oocytes injected with mouse brain mRNA. GABA (10 microM) response was inhibited by ENX in a dose-dependent manner, and IC50 of ENX was 96 microM. Moreover, the inhibitory effect of ENX was 80-fold potentiated in the presence of 10 microM FLB. The GABAA-antagonistic interaction between these two drugs in vitro was considered a possible mechanism of convulsant reaction after concomitant administration of NQs and NSAIDs in vivo.

Animals↗

PubMed1993

The influence of glucagon on the hepatic transport of taurocholate in isolated perfused rat liver: kinetic analysis by the multiple indicator dilution technique.

Glucagon has been demonstrated to stimulate the uptake of bile acid in isolated rat hepatocytes (Am. J. Physiol., 249, G427 (1985)). In the present study, we determined the influence of glucagon on the hepatic transport of a bile acid, taurocholate (TCA), in isolated rat livers. A single-pass perfusion and a rapid-injection, multiple indicator dilution method were employed. The hepatic availability at steady-state was 0.04. With the presence of glucagon in the perfusate (from 10(-9) to 10(-7) M), the bile flow rate was stimulated by 30%, while hepatic availability was decreased from 0.04 to 0.02 with a stepwise increase in glucagon concentration. Thirty min after the infusion of glucagon (300 nM), [3H]TCA and [14C]inulin were injected in a bolus state into the portal vein, and the outflow was collected at 1.0 s intervals over 30 s. Glucagon decreased the instantaneous hepatic availability by 50% compared to the control level, and was thus compatible with the steady-state experiments. In the control experiment, the influx clearance (PSinf) was 20 times higher than the efflux clearance (PSeff). Glucagon (300 nM) in the perfusate enhanced PSinf by 50% of the control, whereas sequestration clearance (CLseq) and the biliary excretion rate constant remained unchanged. PSeff was stimulated to 2 times the control, but still remained much smaller than CLseq. Based on the comparison of PSinf, PSeff and CLseq, the rate-determining process of TCA hepatic elimination was the influx process in both the presence and absence of glucagon. Taken together, the enhancement of the influx process was responsible for the decrease in TCA hepatic availability caused by glucagon.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Effect of basic drugs on the hepatic uptake of ouabain by sinusoidal plasma membrane vesicles isolated from rat liver.

Although antiarrhythmic drugs are used to treat digitalis-induced cardiac disorders, some of these drugs have been reported to increase the serum digoxin concentration in patients, causing the severe side-effects. We have previously shown that many basic drugs including antiarrhythmic drugs inhibited the hepatic uptake of cardiac glycosides into isolated rat hepatocytes, which could be a cause for the increased serum digoxin concentration. The present study was designed to examine the mechanism of this inhibition using isolated rat sinusoidal plasma membrane vesicles. The effect of nine basic drugs (dipyridamole, nifedipine, verapamil, chlorpromazine, lidocaine, quinidine, ajmaline, disopyramide, and propranolol) on the uptake of ouabain was studied. Quinidine reduced the initial uptake rate of ouabain (30 s) while it did not change the uptake of ouabain in an equilibrium condition (30 min). Other basic drugs, such as verapamil, dipyridamole, and nifedipine also significantly reduced the initial uptake rate of ouabain. These basic drugs had no effect on the membrane fluidity. The inhibitory effects on the vesicular uptake were significantly correlated with the inhibitory effects on ouabain uptake by the isolated rat hepatocytes. These findings may suggest that the mechanism of the inhibition involves the inhibition of the transport process via the sinusoidal plasma membrane.

Animals↗

PubMed1992

Nonlinear pharmacokinetics of hepatobiliary transport of rose bengal in rats after i.v. bolus administration with varying doses.

To investigate the nonlinear kinetics in the hepatobiliary transport of rose bengal (RB), the time profiles of plasma concentration and biliary excretion rate after its i.v. administration at various doses were measured in rats. The total body clearance decreased remarkably with increased dose. The hepatic uptake clearance also showed a similar dose dependency, and saturation of hepatic uptake at least partly accounts for the dose-dependent change in total body clearance. The peak biliary excretion rate approached the transport maximum (approximately 150 nmol min-1 kg-1) with increased dose. To further clarify which process in RB hepatobiliary transport has nonlinearity, we analysed thus obtained data based on a three-compartment model. The hepatic uptake and sequestration rate constants decreased remarkably with increased dose. The initial hepatic uptake rates assessed from the plasma disappearance rate during the early phase fit well to the Michaelis-Menten equation with a saturable and a nonsaturable component. The maximum uptake velocity and Michaelis constant were 4.7 mumol min-1 kg-1 and 360 microM, respectively. That hepatic uptake has a much higher capacity (about 30 fold) than biliary excretion suggests that biliary excretion can be a rate-determining process in the overall hepatobiliary transport of RB. We conclude that the saturation of both hepatic uptake and biliary excretion could be the main causes for the nonlinear pharmacokinetics of hepatobiliary transport of RB.

Animals↗