Published papers

To elucidate the role of P-glycoprotein in human placenta, we examined its expression in placenta, and the transcellular transport and uptake of P-glycoprotein substrates in cultured human placental choriocarcinoma epithelial cells (BeWo cells). The uptake of [3H]vinblastine and [3H]vincristine into BeWo cells was increased in the presence of a metabolic inhibitor, sodium azide. The basolateral-to-apical transcellular transport of [3H]vinblastine, [3H]vincristine and [3H]digoxin was greater than the apical-to-basolateral transcellular transport. In the presence of cyclosporin A, the basolateral-to-apical transcellular transport of [3H]vinblastine, [3H]vincristine and [3H]digoxin was significantly increased, and the apical-to-basolateral transcellular transport was decreased. The uptake of [3H]vinblastine, [3H]vincristine and [3H]digoxin into BeWo cells was significantly enhanced in the presence of several inhibitors, such as verapamil or mouse monoclonal antibody anti-P-glycoprotein MX-MDR (MRK16) as well as cyclosporin A. Although progesterone significantly enhanced the uptake of [3H]vinblastine, [3H]vincristine and [3H]digoxin into BeWo cells, the uptake of [3H]progesterone was not affected by these inhibitors. Immunoblot analysis revealed that P-glycoprotein with a molecular weight of 172 kDa was expressed in BeWo cells and isolated trophoblast cells. Furthermore, P-glycoprotein was detected in human placental brush-border membrane vesicles, but not in human placental basolateral membrane vesicles. In conclusion, these data suggest that P-glycoprotein is expressed on the brush-border membrane (maternal side) of human placental trophoblast cells. P-Glycoprotein is considered to regulate the transfer of several substances including vinblastine, vincristine and digoxin from mother to fetus, and to protect the fetus from toxic substances. (C) 2000 Elsevier Science B.V.

Hypokalaemia is one of the important risk factors for development of torsades de pointes. We recently reported that hypokalaemia increased the electrocardiographic QT interval in rats treated with quinidine, but did not alter the arrhythmogenic potency of quinidine. In this study, we have investigated the influence of extracellular potassium concentration ([K+](o)) on the inhibition of several types of cardiac potassium currents by quinidine. Such types of currents include the delayed rectifier potassium current (I(K)), the transient outward current (I(to)), and the inward rectifier potassium current (I(K1)), as measured in isolated rat ventricular cells using patch-clamp techniques. Concentration-dependent effects of quinidine on I(K), I(to), and I(K1) were evaluated under both normal ([K+](o) = 5.4 mM) and hypokalaemic ([K+](o) = 3.5 mM) conditions. In contrast to both I(K) and I(to), which were barely influenced by changes in [K+](o), I(K1) was significantly inhibited by hypokalaemia. Furthermore, while quinidine suppressed both I(K) and I(to) in a concentration-dependent manner, the inhibitory potency of quinidine on these currents was not influenced by changes in [K+](o). The respective normal and hypokalaemic IC50 values for quinidine were 11.4 and 10.0 μM (I(K)), and 17.6 and 17.3 μM (I(to)). Although higher concentrations of quinidine were required to inhibit I(K1), the inhibitory potency of quinidine was also found to be insensitive to changes in [K+](o). Thus, in rats, the inhibitory potency of quinidine for the K+ current-types I(K), I(to) and I(K1) is barely influenced by changes in [K+](o). These findings are consistent with our previous report showing that the QT-prolonging potency of quinidine was not altered under hypokalaemic conditions. However, whilst hypokalemia does not affect I(K) or I(to), it can inhibit I(K1) and can result in QT prolongation in-vivo.

Purpose: Aprepitant is used with dexamethasone and 5-HT3 receptor antagonists as an antiemetic treatment for chemotherapy, including cisplatin. Aprepitant is a substrate of cytochrome P450 (CYP) 3A4 and is known to cause its inhibition and induction. In addition, dexamethasone is a CYP3A4 substrate that induces CYP3A4 and CYP3A5 expression. In this study, we aimed to quantitatively evaluate the profile of CYP3A activity using its endogenous markers in non-small cell lung cancer patients receiving a standard cisplatin regimen with antiemetics, including aprepitant. Methods: Urinary 11β-hydroxytestosterone (11β-OHT)/testosterone concentration ratio and plasma 4β-hydroxycholesterol (4β-OHC) concentrations were measured before and after cisplatin treatment (days 1, 4, and 8). CYP3A5 was genotyped, and plasma aprepitant concentrations were measured on day 4 to examine its influence on CYP3A endogenous markers. Results: The urinary 11β-OHT/testosterone concentration ratio in the 35 patients included in this study increased by 2.65-fold and 1.21-fold on days 4 and 8 compared with day 1, respectively. Their plasma 4β-OHC concentration increased by 1.46-fold and 1.66-fold, respectively. The mean plasma aprepitant concentration on day 4 was 1,451 ng/mL, which is far lower than its inhibitory constant. The allele frequencies of CYP3A5*1 and CYP3A5*3 were 0.229 and 0.771, respectively. In patients with the CYP3A5*1 allele, the plasma 4β-OHC concentration was significantly lower at baseline but more potently increased with chemotherapy. Conclusion: CYP3A activity was significantly induced from day 4 to day 8 in patients receiving cisplatin and three antiemetic drugs.

We retrospectively analyzed the bone mineral density (BMD) of postmenopausal Japanese women taking an aromatase inhibitor (AI), exemestane, anastrozole or letrozole, and calculated the decrease rate constant of BMD in each individual to compare the influence of the three AIs on BMD. We also aimed to evaluate the preventive effect of bisphosphonates (BPs) on the AI-induced decrease in BMD. The decrease rate constant of BMD (ke) in each individual was determined as a slope of linear regression of the relationship between time and logarithm of BMD value in each patient during the AI therapy. To compensate for the age-related change in BMD level, we estimated the age-related decrease rate constant of BMD (ke,0) in healthy Japanese postmenopausal women from the literature. AIs decreased BMD with a ke value of -0.0329 yr-1, which was 4.7-fold larger than the ke,0 value of -0.00699 yr-1. No significant difference was detected in the influence on BMD among AIs. Co-administration of BP ameliorated the ke value to -0.0117 yr-1, a value similar to ke,0. The influence of AIs on BMD was quantitatively evaluated by using the decrease rate constant of BMD (ke). The present study also suggests that BPs may be useful to prevent the decrease in BMD induced by AIs. © 2013 by the Japanese Society for the Study of Xenobiotics (JSSX).

Purpose. Some methoxyflavones (MFs) are known to inhibit the function of P-glycoprotein. The aim of this study is to characterize the reversal of multidrug resistance (MDR) by MFs. Methods. The effects of 19 MFs, including 3,5,6,7,8,3′,4′-heptamethoxyflavone, nobiletin, and tangeretin, and flavone on the uptake of [3H]vincristine into an adriamycin-resistant variant of human chronic myelogenous leukemia (K562/ADM) cells were investigated. Potentiation of vincristine-induced growth inhibition by these MFs was also tested in K562/ADM cells by means of WST-1 [2-(4-iodophenyl)-3-(4- nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium] assay. Results. All MFs (20 μM) tested increased the uptake of [3H]vincristine. 3,5,6,7,8,3′,4′-heptamethoxyflavone, nobiletin, tangeretin, quercetagetin and quercetin pentamethylether showed especially potent effects. The increase in the uptake of [3H]vincristine was proportional to the number of methoxyl moieties. While substitution with a methoxyl moiety at the C3 position was the most influential, methoxyl substitution at both the C3′ and C5′ positions resulted in a decrease in the potentiation of uptake. Furthermore, there was a significant correlation between the potencies for increasing [3H]vincristine uptake and for growth inhibition assessed by WST-1 assay. Conclusions. MFs increased the uptake of [ 3H]vincristine into MDR cells and exhibited MDR-reversing effects. Their potencies were influenced by the number and positions of the methoxyl moieties. © 2007 Springer Science+Business Media, LLC.

The objective of this study was to examine the effect of macrolide antibiotics, clarithromycin, erythromycin, roxithromycin, josamycin and azithromycin, on the hepatic uptake of digoxin. The uptake of [3 H]digoxin was studied in rats in vivo, using the tissue-sampling single-injection technique, and in isolated rat hepatocytes in vitro. The uptake of [3H]digoxin into rat hepatocytes was concentration-dependent with a Michaelis constant (Km) of 445 nM. All the macrolide antibiotics inhibited the uptake of [3H]digoxin into rat hepatocytes in a concentration-dependent manner. However, clarithromycin did not affect the in vivo hepatic uptake of digoxin in rats. The in vivo permeability-surface area product of digoxin for hepatic uptake (PSinf) was estimated to be 12.5 ml/min/g liver from the present in vitro data, which is far larger than the hepatic blood flow rate (1.4 ml/ min/g liver). Macrolide antibiotics at clinically relevant concentrations inhibit digoxin uptake by rat hepatocytes in vitro, but not in vivo, probably because hepatic uptake of digoxin in rats is blood flow-limited. Clinically observed digoxin-macrolide interaction in humans could be due to macrolide inhibition of hepatic digoxin uptake, if the uptake is permeation-limited. Copyright © 2007 John Wiley & Sons, Ltd.

The aim of this study was to verify an approach for calculating pharmacokinetic parameters suitable for adjusting dosage regimens in patients with renal dysfunction. We carried out a retrospective analysis of the pharmacokinetic profiles of 12 new quinolone antibiotics and 11 angiotensin-converting enzyme inhibitors (ACEIs) in patients with normal and impaired renal function to obtain the renal excretion ratio (Rrenal) of each drug. We demonstrated that the pharmacokinetics of each drug in a patient with renal dysfunction can be adequately estimated using the Rrenal value of each drug together with the creatinine clearance as an index of the individual's renal function. Using the Rrenal value obtained, we could successfully simulate pharmacokinetic profiles of the drugs in publications other than that used to obtain the Rrenal values. On the other hand, age-related changes in the pharmacokinetics of new quinolone antibiotics are not always adequately predicted using the Rrenal value compared to using creatinine clearance alone as an index, and the reasons for this are not fully understood. These results demonstrate that dosage regimens of quinolone antibiotics and ACEIs in patients with renal dysfunction can be adequately optimized using the Rrenal value for each drug using the present approach. © 2006 Dustri-Verlag Dr. K. Feistle.

Most known interactions between herbal extracts and drugs involve the inhibition of drug-metabolizing enzymes, but little is yet known about the possible role of transporters in these interactions. In this study, we have examined the effects of herbal extracts used in dietary supplements on the function of organic anion-transporting polypeptide B (OATP-B; OATP2B1), which is expressed on human intestinal epithelial cells and is considered to be involved in the intestinal absorption of various drugs. Specifically, the effects of 15 herbal extracts on uptake of estrone-3-sulfate, a typical OATP-B substrate, by human embryonic kidney 293 cells stably expressing OATP-B were evaluated. At concentration levels considered likely to be attainable in the human intestine, extracts of bilberry, echinacea, green tea, banaba, grape seed, ginkgo, and soybean potently inhibited estrone-3-sulfate uptake by 75.5, 55.5, 82.1, 61.1, 64.5, 85.4, and 66.8%, respectively (P < 0.01). The inhibitory effect of ginkgo leaf extract was concentration-dependent (IC50 = 11.2 ± 3.3 μg/ml) and reversible. Moreover, flavonol glycosides and catechins significantly inhibited the function of OATP-B, suggesting that the inhibitory effects of the herbal extracts on OATP-B may be primarily attributable to flavonoids. The extracts of mulberry, black cohosh, and Siberian ginseng moderately (but significantly) inhibited estrone-3-sulfate uptake by 39.1, 47.2, and 49.2%, respectively (P < 0.05). Extracts of barley, Job's tears, rutin, rafuma, and passionflower were ineffective. These results suggest that coadministration of some dietary supplements may decrease the absorption of orally administered substrates of OATP-B. Copyright © 2006 by The American Society for Pharmacology and Experimental Therapeutics.

Background: Irinotecan (CPT-11) is clinically known to cause severe diarrhea and gastrointestinal damage. Recently, we have reported that CPT-11-induced gastrointestinal damage is associated with the upregulation of intestinal P-glycoprotein (P-gp) expression and decreased absorption of its substrate, dabigatran etexilate (DABE), using a rat model. However, the P-gp activity or its contribution to the decreased absorption remains unclear. The aim of this study was to quantitatively evaluate how P-gp activity changes in rats with CPT-11-induced gastrointestinal damage, as assessed by the absorption of digoxin (DGX), a typical P-gp substrate. Methods: Male Sprague-Dawley rats were intravenously administered CPT-11 at a dose of 60 mg/kg/day for 4 days to induce gastrointestinal damage. Then, the rats were administered DGX orally (40 μg/kg), after some of them were orally administered clarithromycin (CAM; 10 mg/kg), a P-gp inhibitor. DGX (30 μg/kg) was administered intravenously to determine the bioavailability (BA). The rats’ DGX plasma concentration profiles were determined using LC-MS/MS. Results: CPT-11 treatment decreased the maximum concentration (Cmax) and area under the plasma concentration-time curve (AUCpo) of DGX, which does not contradict to the DABE study. Although in the CPT-11-treated group the BA of DGX was significantly decreased to 40% of the control value, CAM did not affect the BA of DGX in the CPT-11-treated group. Conclusions: Increased P-gp expression in rats with CPT-11-induced gastrointestinal damage is not necessarily associated with increased P-gp activity or contribution to the drug absorption in vivo. The decreased DGX absorption observed in this study might be attributable to other factors, such as a reduction in the absorptive surface area of the gastrointestinal tract.

Organic anion transporting polypeptide (OATP) 2B1 is expressed in the intestine and liver, and OATP2B1-mediated transport of estrone 3-sulfate is pH-dependent and consists of: the high-affinity component (Hc) and low-affinity component (Lc). This study aimed to evaluate the influence of pH on the transport kinetics of each component, along with the inhibitory nature of ten OATP2B1 inhibitors. The Michaelis constants (Km) were 4-fold and 1.5-fold lower at pH 6.3 than at pH 7.4, for Hc and Lc respectively. The inhibitory potencies of diclofenac, indomethacin, and ibuprofen towards Hc were 1.5–4.3 fold lower at pH 6.3 than at pH 7.4. Contrastingly, inhibitory potencies towards Lc were 9.0–52 fold lower at pH 7.4. Similarly, the inhibitory effect of naproxen was stronger towards Hc at pH 6.3 and towards Lc at pH 7.4. On the other hand, celecoxib selectively inhibited Lc transport at pH 7.4. Rifampicin inhibited both components at pH 6.3 and 7.4 to a similar extent, while bromosulphophthalein, naringin, and gefitinib selectively inhibited Hc irrespective of pH. Fexofenadine inhibited neither component. In conclusion, the transport affinities of both Hc and Lc were enhanced under acidic conditions. The influence of pH on the inhibitory potency towards each component varied among the inhibitors.

Several grapefruit juice bioflavonoids, including quercetin, are reported to stimulate P-glycoprotein-mediated drug efflux from cultured tumor cells. To see whether these bioflavonoids alter the permeation of vincristine across the blood-brain barrier, we conducted experiments with cultured mouse brain capillary endothelial cells (MBEC4 cells) in vitro and ddY mice in vivo. The steady-state uptake of [3H]vincristine by MBEC4 cells was decreased by 10 μM quercetin, but increased by 50 μM quercetin. Similarly, the in vivo brain-to-plasma concentration ratio of [3H]vincristine in ddY mice was decreased by coadministration of 0.1 mg/kg quercetin, but increased by 1.0 mg/kg quercetin. Kaempferol had a similar biphasic effect on the in vitro uptake of [3H]vincristine. Other aglycones tested (chrysin, flavon, hesperetin, naringenin) increased [3H]vincristine uptake in the 10-50 μM range, and glycosides (hesperidin, naringin, rutin) were without effect. We then addressed the mechanism of the concentration-dependent biphasic action of quercetin. Verapamil, a P-glycoprotein inhibitor, inhibited the efflux of [3H]vincristine from MBEC4 cells, while 10 μM quercetin significantly stimulated it. The uptake of [3H]vincristine by MBEC4 cells was increased by inhibitors of protein kinase C, but decreased by phorbol 12-myristate-13- acetate (PMA), as well as by 10 μM quercetin. The phosphorylation level of P-glycoprotein was increased in the presence of 5 μM quercetin or 100 nM PMA, but decreased by the protein kinase C inhibitor H7 (1-(5- isoquinolinesulfonyl)-2-methylpiperazine, 30 μM). We conclude that low concentrations of quercetin indirectly activate the transport of [3H]vincristine by enhancing the phosphorylation (and hence activity) of P- glycoprotein, whereas high concentrations of quercetin inhibit P- glycoprotein. Our results indicate that patients taking drugs which are P- glycoprotein substrates may need to restrict their intake of bioflavonoid- containing foods and beverages, such as grapefruit juice. (C) 2000 Elsevier Science B.V.

1. The presence of inhibitors of drug efflux transporters, such as P-glycoprotein (P-gp), in grapefruit juice (GFJ) was confirmed based on the uptake of [3H]-vinblastine (VBL) by Caco-2 cells. 2. The uptake of [3H]-VBL by Caco-2 cells was significantly increased by the ethyl acetate extract of GFJ as well as by cyclosporin A. The extract was separated on a Cosmosil column and the eluate with 60% methanol increased [3H]-VBL uptake, while the activity to inhibit CYP3A4 was greatest in the 70 and 80% eluates. 3. These results show that the major inhibitor of efflux transport of VBL is different from that of CYP3A4. 4. Further separation of the 60% methanol eluate afforded dihydroxybergamottin (DHBG). Both ethyl acetate extract of GFJ and DHBG increased steady-state [3H]-VBL uptake by LLC-GA5-COL300 cells. Besides DHBG, other furanocoumarins contained in GFJ, such as bergamottin, FC726, bergaptol and bergapten, increased the steady-state uptake of [3H]-VBL by Caco-2 cells. 5. The order of inhibitory potency of these compounds was FC726 > DHBG > bergamottin > bergapten > bergaptol. While, the IC50 values for inhibition of CYP3A4 were 0.075, 0.45, 1.0, 1.0 and > 20 μM, respectively. Bergaptol specifically inhibited VBL efflux. 6. DHBG was thus identified as a candidate for inhibitors of VBL transport, together with other furanocoumarins. Moreover, partly involvement of the P-gp inhibition was suggested. 7. Therefore, the inhibition of efflux transport of drugs as well as of drug metabolism by CYP3A4 could be an important cause of drug-GFJ interaction.

Objective Plasma drug concentrations are generally considered to reflect efficacy and pharmacokinetics more directly than those in whole blood. However, whole blood has been selected as the matrix to monitor concentrations of tacrolimus (FK506), because it is difficult to accurately measure plasma FK506 concentrations. Because FK506 highly and saturably binds in blood cells, a change in hematocrit value (Hct) may affect FK506 pharmacokinetics. Therefore, we investigated effects of Hct on FK506 pharmacokinetics. Methods First, we analyzed data on FK506 distribution among human blood cells in vitro. Briefly, we employed an equation, which describes saturable binding of FK506 to blood cells, and simulated plasma FK506 concentrations and clearances using the above equation with respect to a variable Hct. Subsequently, we retrospectively analyzed dosages and whole blood FK506 concentrations to predict plasma FK506 concentrations in living donor transplant recipients. Results In the simulation study, the Hct changed plasma FK506 concentrations and clearances based in whole blood. In living donor liver transplant recipients, whole blood FK506 concentrations were maintained within a therapeutic range, while the Hct varied after transplantation. The correlation of Hct with the ratio of dose/trough concentrations of FK506 (D/C) in plasma (D/Cp) (R = -0.23, n = 343) was weaker than that for D/C in whole blood (D/CWB) (R = -0.53, n = 343). Conclusion Hct may be an important factor affecting the pharmacokinetics of FK506 in living donor liver transplantation recipients. It may be necessary to take Hct into consideration in the FK506 dosing regimen, especially when the Hct is low.

The absolute oral bioavailability (BA) of drugs are yet to be determined, and intravenous pharmacokinetic studies are currently considered indispensable for determining the BA values of oral drugs. The aim of this study was to develop and validate a novel approach to estimating BA values without intravenous pharmacokinetic data. Based on the drug inclusion criteria, such as exhibiting a urinary recovery rate of (Ru) of ≥20% in a clinical study, 13 drugs were included in the present study, and pharmacokinetic data for them were collected from the literature. The fraction excreted unchanged into urine (fe) was calculated for healthy subjects by dividing the Ru value by the total recovery rate. The contribution of renal excretion to total clearance from the systemic circulation (Rren) was estimated by subjecting oral clearance and creatinine clearance to regression in subjects with normal and impaired renal function. BA was estimated as fe/Rren and compared with the observed BA (BAobs). The predicted BA values for 9 drugs fell within ±20% of their BAobs. The examined approach makes it possible to estimate BA values for drugs with mean renal excretion values in healthy subjects and oral clearance in subjects with various renal function, without intravenous pharmacokinetic data.

1 We investigated the effects of grapefruit juice (GFJ) and orange juice (OJ) on drug transport by MDR1 P-glycoprotein (P-gp) and multidrug resistance protein 2 (MRP2), which are efflux transporters expressed in human small intestine. 2 We examined the transcellular transport and uptake of [ 3H]vinblastine (VBL) and [ 14C]saquinavir in a human colon carcinoma cell line (Caco-2) and in porcine kidney epithelial cell lines transfected with human MDR1 cDNA and human MRP2 cDNA, LLC-GA5-COL150, and LLC-MRP2, respectively. 3 In Caco-2 cells, the basal-to-apical transports of [ 3H]VBL and [ 14C]saquinavir were greater than those in the opposite direction. The ratio of basal-to-apical transport to apical-to-basal transport of [ 3H]VBL and [ 14C]saquinavir by Caco-2 cells was reduced in the presence of MK571 (MRPs inhibitor), verapamil (P-gp inhibitor), cyclosporin A (inhibitor of both), 50% ethyl acetate extracts of GFJ and OJ, or their components (6′,7′-dihydroxybergamottin, bergamottin, tangeretin, hepatomethoxyflavone, and nobiletin). 4 Studies of transport and uptake of [ 3H]VBL and [ 14C]saquinavir with MDR1 and MRP2 transfectants showed that VBL and saquinavir are transported by both P-gp and MRP2. GFJ and OJ components inhibited the transport by MRP2 as well as P-gp. However, their inhibitory potencies for P-gp or MRP2 were substrate-dependent. 5 The present study has revealed that GFJ and OJ interact with not only P-gp but also MRP2, both of which are expressed at apical membranes and limit the apical-to-basal transport of VBL and saquinavir in Caco-2 cells.

The drug interaction between new quinolone antibiotics (NQs) and polyvalent metal cation products, leading to a significant decrease in the absorption of NQ, is considered to be attributable to the formation of poorly absorbable chelate and physicochemical adsorption of NQs to cation products. To clarify the mechanisms of this drug interaction in detail, we investigated the effects of Al3+ or Mg2+ on the membrane permeation profile of ciprofloxacin (CPFX) across human colon carcinoma cell lines (Caco-2) in monolayer culture, and characterized the adsorption nature of CPFX to polyvalent metal cation products under physiological conditions. As a result, Al3+ or Mg2+ partially but not fully impaired the permeation of CPFX across Caco-2 monolayer up to 30% or 60% of control, respectively. Physicochemical adsorption of CPFX to cation products was not observed under physiological pH. In conclusion, two possible mechanisms investigated, the decrease in the permeability of CPFX by chelate formation and adsorption of CPFX to polyvalent metal cation products, may partially but not fully explain the extent of the drug interaction clinically observed.

BACKGROUND: TS-1 is a combination preparation of tegafur, a prodrug of 5-fluorouracil (5-FU), with gimeracil, a potent inhibitor of dihydropyrimidine dehydrogenase (DPD), which mediates the inactivation of 5-FU. UFT is a combination preparation of tegafur with uracil, which also inhibits DPD, though less potently; UFT has a higher content of tegafur than that in TS-1. We aimed to develop a pharmacokinetic model to describe the kinetics of tegafur and 5-FU after the administration of TS-1 and UFT. METHODS: We developed a model incorporating the inhibition of DPD by gimeracil and uracil, and fitted the model to the observed kinetics of tegafur and 5-FU after the administration of TS-1 and UFT. Then, we simulated the plasma 5-FU profiles in patients with renal dysfunction and those after replacement of TS-1 with UFT and compared them with the observed profiles. RESULTS: The developed model could appropriately describe the plasma concentration profiles of 5-FU and tegafur after the administration of TS-1 in patients with normal and impaired renal function. CONCLUSION: The developed model may be useful to optimize the dosage regimen of TS-1 under various clinical conditions.

Here we present a method for measuring the permeability coefficient-surface area product (PS) values at the blood-brain barrier in mice, using the in situ brain perfusion technique originally developed for rats by Takasato et al. (Am J Physiol Heart Circ Physiol 247: H484-H493, 1984). Retrograde infusion into the right external carotid artery increased the carotid perfusion pressure in proportion to the perfusion rate. Intravascular volume and cerebral perfusion fluid flow at a perfusion rate of 1.0 ml/min in mice were similar to those in rats. In addition, the contribution of systemic blood to total flow in the hemisphere was small (only 3.2%). These findings indicated that this perfusion rate is suitable for mice. The PS values of more than 20 different compounds were determined in mice by using the in situ brain perfusion technique, and comparisons were made with data from rats. There was a close relationship (1:1) between the PS values in mice and rats, indicating that brain capillary permeabilities are similar in mice and rats.

A simple method for the quantitative determination of erythromycin (EM) concentrations in rat plasma and liver by high-performance liquid chromatography with amperometric detection was developed. EM was extracted from 200 μl of plasma or liver homogenate sample under sodium hydroxide alkaline conditions with tert.-butyl methyl ether. Oleandomycin was used as an internal standard. The recovery rate of EM was up to 100%. The detector cell potential for the oxidation of EM was +1100 mV. The calibration curves were linear over the concentration ranges 0.1-20.0 μg/ml for plasma and 0.5-100.0 μg/g for liver. The method was applied to the determination of the plasma and liver concentrations of EM in rats after intravenous administration (50 mg/kg dose). The method presented here has proved to be of great use for the investigation of the pharmacokinetic characteristics of EM in small animals such as rats.

In this study, a high-performance liquid chromatographic method was developed for the quantitative determination of erythromycin (EM), roxithromycin (RXM), and azithromycin (AZM) in rat plasma with amperometric detection under a standardized common condition using clarithromycin (CAM) as an internal standard. This method was also proved to be applicable for the determination of CAM by employing RXM as an internal standard. Each drug was extracted from 150 μl of plasma sample spiked with internal standard under an alkaline condition with tert.-butyl methyl ether. The detector cell potential for the oxidation of the drugs was set at +950 mV. The linearity of the calibration curves were preserved over the concentration ranges of 0.1-10 μg/ml for EM and RXM, and 0.03-3.0 μg/ml for CAM and AZM. Coefficients of variation and relative error were less than 9% and ±7%, respectively. The analytical method presented here was proved to be useful for the investigation of the pharmacokinetic characteristics of EM, CAM, RXM, and AZM in rats. (C) 2000 Elsevier Science B.V.