Search

Although it is recognized that pharmacokinetic processes follow exponential processes, area under the curve (AUC ) estimations are frequently carried out using linear trapezoidal methods. This is justified based on the fact that most human studies are carried out following oral dosing, and it is believed that a logarithmic trapezoidal method will markedly underpredict the areas for increasing drug concentrations. Here we show that increasing concentrations can be estimated more accurately using a new simple logarithmic method for increasing concentrations. Further, no previous discussion of linear versus logarithmic calculation has been published for area under the moment curve (AUMC ) calculations. Thus, the derivation of a new methodology for calculating area values for logarithmic processes exhibiting increasing values of concentrations and moments is shown. Use of the methodology is presented and compared with the presently utilized linear approach. Pharmacokinetic absorption and elimination processes are primarily assumed to follow an exponential process, so that measurements of concentrations over time exhibit exponential versus linear relationships with time. Therefore, calculations of AUC should be more accurate using logarithmic methods than with linear methods. It is recognized that for decreasing concentrations with time, more accurate calculations of AUC will be estimated using the logarithmic trapezoidal rather than the linear trapezoidal rule. However, it was believed that logarithmic AUC calculations would be more inaccurate for increasing concentrations and moment values. Therefore, there is no generally recommended rule as to how AUCs should be estimated. We show here that a simple logarithmic methodology can be utilized for all increasing values except to the first measurement after time zero. It appears that for concentration-time curves, AUC will be best estimated using logarithmic methods for both increasing and decreasing concentrations. However, it appears that for well-designed sampling schedules, the increased accuracy of using logarithmic trapezoidal methods versus using linear trapezoidal methods is not sufficient to give significant errors in clearance calculations. In contrast, here we show that using linear area calculations for AUMC is probably more accurate than using any combination of linear and logarithmic methods.

Drug disposition after topical application to the skin has not been fully elucidated, especially after repeated application. We conducted a clinical trial to evaluate the pharmacokinetics in the stratum corneum of healthy adults after repeated application of lanoconazole cream as a model drug. We applied 25 mg of 1% lanoconazole cream onto the pre-specified areas on the participants' back once daily for 5 days. The stratum corneum was sampled twice on each study day using a standardized tape-stripping method, and the amount of lanoconazole contained in the samples was quantified using the tandem mass spectrometry method. The obtained data were used to evaluate lanoconazole pharmacokinetics in the stratum corneum. The amount of lanoconazole in the stratum corneum after once daily repeated administration reached a steady state on day 3, and it was eliminated from the stratum corneum with a half-life of approximately 11 h after discontinuing application.

A selective b3-adrenoceptor agonist, mirabegron, an established alternative to antimuscarinic therapy for patients with overactive bladder (OAB), has been shown to induce additional effects against receptors, transporters, and hepatic enzymes. The present study aimed to elucidate the effects of mirabegron on muscarinic receptors in the rat bladder using radioligand binding and functional assays. Mirabegron (0.1-100 mM) inhibited specific [N-methyl-3H]scopolamine chloride ([3H]NMS) binding in the bladder and other tissues of rats in a concentration-dependent manner. Binding affinity in the bladder was similar to that in the heart, and significantly lower than those in the submaxillary gland and brain. Mirabegron exerted the concentration-dependent relaxation of carbachol-induced contractions in the rat isolated bladder. Further analyses using a two-site model revealed that the relative quantities of high and low affinity components for mirabegron were 44.5 and 55.5%, respectively. Respective EC50 were 87.3 nM and 10.7 mM. Muscarinic receptor occupancy in the human bladder estimated from the receptor binding affinity and pharmacokinetics of mirabegron was 37-76% until 24 h after the single oral administration of 50 mg mirabegron. The present study is the first to demonstrate that mirabegron may relax the detrusor smooth muscle not only by b3-adrenoceptor activation, but also muscarinic receptor blockade. Significance Statement Mirabegron, the first selective b3-adrenoceptor agonist, represents an alternative to antimuscarinic agent for management of overactive bladder (OAB). The present study aimed to clarify whether or not mirabegron binds directly muscarinic receptors and affects cholinergic agonist-induced contractions in rat urinary bladder, and to predict muscarinic receptor occupancy in human bladder following oral mirabegron. It has been demonstrated for the first time that mirabegron therapy for patients with OAB may result from not only b3-adrenoceptor activation, but also antagonizing muscarinic receptors.

Royal jelly (RJ) is widely used as a cosmetic or dietary supplement to relieve various health disorders, such as dry skin, fatigue, and menopause. RJ has been recommended to improve constipation on a commercial basis. However, the detailed mechanisms by which RJ influences intestinal motility and whether RJ improves constipation remain unclear. Therefore, we investigated the effects of RJ on the motility of mouse ileum both

Aims In addition to potentially progressing to either cirrhosis or hepatocellular carcinoma, non-alcoholic steatohepatitis (NASH) is currently the leading indication for liver transplantation. Nintedanib has been clinically used to treat idiopathic pulmonary fibrosis for many years, but its effects in an animal model of NASH have not been tested. The purpose of this study was to evaluate the effects of nintendanib on NASH in choline-deficient, l -amino acid-defined, high-fat diet (CDAHFD)-fed mice. Main methods Male C57BL/6 mice were fed a CDAHFD for 6 weeks to induce NASH with liver fibrosis, and they were administered nintedanib (60 mg/kg/day) or distilled water orally in the last 2 weeks of the feeding period. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), triglyceride, and non-esterified fatty acids concentrations were measured. Serum cytokeratin 18 fragment (CK18) was detected using ELISA. Liver tissue sections from mice were stained with hematoxylin-eosin and Masson's trichrome to assess the level of steatohepatitis and fibrosis. Key findings CDAHFD-fed mice exhibited higher serum ALT, AST, and ALP levels compared with Control mice. A significant increase in the serum CK18 level was observed in the NASH group compared with the Control group. CDAHFD feeding also enhanced steatohepatitis and hepatic fibrosis pathological features, which were reduced after nintedanib treatment. Significance Nintedanib exerted anti-inflammatory and anti-fibrotic effects in CDAHFD-induced NASH mice.

We evaluated the effects of anticholinergic drugs principally used for the therapy of overactive bladder (OAB) on the activity of P-glycoprotein, an efflux transport protein, in Caco-2 cells. The time-dependent changes in the fluorescence of residual rhodamine 123, a P-glycoprotein activity marker, in the apical region of Caco-2 cells were measured in the presence of anticholinergic drugs using time-lapse confocal laser scanning microscopy. The effect of anticholinergic drugs on human P-glycoprotein ATPase activity was also measured. The fluorescence of residual rhodamine 123 in untreated Caco-2 cells decreased over time. The gradual decrease in the fluorescence was significantly inhibited by treatment with cyclosporine A, darifenacin, and trospium. In contrast, oxybutynin, N-desethyl-oxybutynin (DEOB), propiverine, and its active metabolites (M-1, M-2), imidafenacin, solifenacin, or tolterodine had little effect on the efflux of rhodamine 123. P-Glycoprotein ATPase activity was increased by darifenacin. Darifenacin and trospium reduced the rhodamine 123 transfer across the apical cell membrane. These data suggest that darifenacin and trospium interact with P-glycoprotein. Additionally, darifenacin influenced P-glycoprotein ATPase activity. These results suggest that darifenacin may be a substrate of P-glycoprotein. This study is the first paper to test simultaneously the effects of 10 anticholinergic drugs used currently for the therapy of OAB, on the P-glycoprotein.

In this study, we aimed to study the effects of ICI204,448, naloxone methiodide and levocetirizine on the scratching behavior induced by intradermal injection of a ?-opioid antagonist, nor-binaltorphimine (nor-BNI), into the rostral back of ICR mice were investigated.Male ICR mice weighing 30?35 g were used. The number of scratching episodes were counted for 60 min after i.d. injection of nor-BNI.nor-BNI dose dependently increased in the number of scratching episodes in ICR mice. nor-BNI-induced scratching behavior was inhibited by not only nalfurafine but also ICI204,448, a peripherally selective ?-opioid agonist. Naloxone and naloxone methiodide, a peripherally restricted ?-opioid antagonist, also inhibited nor-BNI-induced scratching behavior. Scratching behavior induced by nor-BNI was inhibited by chlorpheniramine as well as levocetirizine, a third-generation HThese results suggest that scratching behavior induced by this ?-opioid antagonist, nor-BNI, is related to not only central but also peripheral opioid and H

This study evaluated the utility of combination of digoxin (0.25 mg) and rosuvastatin (5 mg) as a new transporter (P‐glycoprotein/breast cancer resistance protein/organic anion‐transporting polypeptide (OATP)1B1/OATP1B3) probe cocktail (Oita combination) for drug–drug interaction (DDI) studies by demonstrating lack of DDI of digoxin on the pharmacokinetics (PKs) of rosuvastatin, as it was already known that rosuvastatin did not affect digoxin PK. This was an open‐label, two‐period study in which the primary end points were the geometric mean ratio (GMR) of the area under the plasma rosuvastatin concentration‐time curve from time zero to last (AUC last) after rosuvastatin administration combined with digoxin to that after rosuvastatin administration alone and its 90% confidence interval (CI). As the GMR of AUC last was 0.974 and its 90% CI was 0.911–1.042, it was judged that digoxin does not affect rosuvastatin PK. Results of this study have rationalized utility of the Oita combination as a transporter probe cocktail for clinical DDI studies.

The present study aimed to directly characterize specific binding sites of tritium ([(3)H])-labeled imidafenacin, a new radioligand for labeling muscarinic receptors, in the bladder and other peripheral or central nervous tissues of rats. Muscarinic receptors in rat tissues were measured by radioligand binding assay using [(3)H]imidafenacin. Specific [(3)H]imidafenacin binding in rat tissues was saturable, reversible, and of high affinity. Estimated dissociation constants (Kd values) were significantly lower in submaxillary gland and prostate and higher in heart than in bladder, indicating lower Kd values in M1 and M3 subtype- than M2 subtype-dominating tissues. Unlabeled imidafenacin and clinically used antimuscarinic agents competed with [(3)H]imidafenacin for binding sites in bladder and other tissues in a concentration-dependent manner, which indicated pharmacological specificity of [(3)H]imidafenacin binding sites. Pretreatment with N-(2-chloroethyl)-4-piperidinyl diphenylacetate (4-DAMP mustard), an irreversible inactivating agent of M3 subtype, significantly decreased the number of [(3)H]imidafenacin binding sites in bladder, submaxillary gland, and colon, but not in heart. [(3)H]imidafenacin labeled muscarinic receptors in M1 and M3 subtype-dominating tissues with higher affinity than [N-methyl-(3)H]scopolamine methyl chloride (NMS). [(3)H]imidafenacin is a useful radioligand to label muscarinic receptors in M1- and M3-dominating tissues with high affinity.

Endothelium-dependent vasodilation via protease-activated receptor 2 (PAR2) is preserved in mesenteric arteries from SHRSP.Z-Leprfa/IzmDmcr rats (SHRSP.ZF) with metabolic syndrome even though nitric oxide (NO)-mediated vasodilation is attenuated. Therefore, we examined the PAR2 mechanisms underlying metabolic syndrome-resistant vasodilation in SHRSP.ZF aortas with ageing. In isolated aortas, the PAR2 agonist 2-furoyl-LIGRLO-amide (2fly) caused vasodilation that was sustained in male SHRSP.ZF until 18 weeks of age, but was attenuated afterwards compared with age-matched Wistar-Kyoto rats (controls) at 23 weeks. In contrast, acetylcholine-induced vasodilation was impaired in SHRSP.ZF already at 18 weeks of age. Treatments of aortas with inhibitors of NO synthase and soluble guanylate cyclase abolished the sustained 2fly- and residual acetylcholine-induced vasodilation in SHRSP.ZF at 18 weeks of age. In the aortas of SHRSP.ZF, 8-bromo-cGMP-induced vasodilation, NO production and cGMP accumulation elicited by 2fly were not different from in the controls. PAR2 agonist increased phospho-Ser1177-eNOS protein content only in SHRSP.ZF aortas. These results indicate that vasodilation mediated by PAR2 is sustained even though NO-dependent relaxation is attenuated with ageing/exposure to metabolic disorders in large-caliber arteries from SHRSP.ZF. PAR2 stimulation of NO production via an additional pathway that targets phosphorylation of Ser1177-eNOS suggests a regulatory mechanism for sustaining agonist-mediated vasodilation in metabolic syndrome.

Metabolic syndrome (MetS) is a combination of clinical disorders that together increase the risk for cardiovascular disease and diabetes. SHRSP.Z-Lepr(fa)/IzmDmcr (SHRSP.ZF) rats with MetS show impaired nitric oxide-mediated relaxation in coronary and mesenteric arteries, and angiotensin II receptor type 1 blockers protect against dysfunction and oxidative-nitrosative stress independently of metabolic effects. We hypothesize that superoxide contributes to functional deterioration in SHRSP.ZF rats. To test our hypothesis, we studied effects of treatment with tempol, a membrane-permeable radical scavenger, on impaired vasodilation in SHRSP.ZF rats. Tempol did not alter body weight, high blood pressure, or metabolic abnormalities, but prevented impairment of acetylcholine-induced and nitroprusside-induced vasodilation in the coronary and mesenteric arteries. Furthermore, tempol reduced the levels of serum thiobarbituric acid reactive substance (TBARS) and 3-nitrotyrosine content in mesenteric arteries. Systemic administration of tempol elevated the expression of soluble guanylate cyclase (sGC) above basal levels in mesenteric arteries of SHRSP.ZF rats. However, acute treatment with tempol or ebselen, a peroxynitrite scavenger, did not ameliorate impaired relaxation of isolated mesenteric arteries. No nitration of tyrosine residues in sGC was observed; however, sGC mRNA expression levels in the arteries of SHRSP.ZF rats were lower than those in the arteries of Wistar-Kyoto rats. Levels of Thr(496)- and Ser(1177)-phosphorylated endothelial nitric oxide synthase (eNOS) were lower in arteries of SHRSP.ZF rats, and acetylcholine decreased Thr(496)-phosphorylated eNOS levels. These results indicated that prolonged superoxide production, leading to oxidative-nitrosative stress, was associated with impaired vasodilation in SHRSP.ZF rats with MetS. Down-regulated sGC expression may be linked to dysfunction, while reduced NO bioavailability/eNOS activity and modified sGC activity due to superoxide production were excluded as pivotal mechanisms.

Metabolic syndrome is a complex of disorders that includes visceral obesity, insulin resistance, hypertension, and dyslipidemia. It is characterized by an increased risk for serious cardiovascular events. Adipocytes are now recognized to contribute to the development of cardiovascular complications in metabolic syndrome via the release of several bioactive substances (adipocytokines). Obesity induces an increase in the volume of perivascular adipose tissue (PVAT), which is located outside the blood vessels. In recent years, PVAT has been reported to produce/release vasoactive adipocytokines. Thus, PVAT can modulate vasomotor function by releasing vasorelaxing/vasocontracting factors, resulting in the development of cardiovascular disease due to metabolic syndrome. By using animal models (SHR/NDmcr-cp rats, SHRSP.Z-Lepr(fa)/IzmDmcr rats, and B6.BKS (D)-Lepr(fa)/J mice), we have demonstrated that chronic oxidative-nitrative stress is closely linked to the development of vascular dysfunction in response to nitric oxide (NO) in resistant arteries with increasing age/exposure to metabolic abnormalities. Further, our recent findings have led us to believe that PVAT helps in the regulation of vasodilation to compensate for the impaired vasodilation observed in pathophysiological conditions in the mesenteric arteries of SHRSP.Z-Lepr(fa)/IzmDmcr rats. However, a breakdown of the compensatory system occurs with long-term exposure to metabolic abnormalities. We propose the concept of the functional regulation of vascular tissue by PVAT in metabolic syndrome.

Objectives The aim of this study was to use time-lapse confocal laser scanning microscopy to establish a more sensitive and specific method for evaluating P-glycoprotein activity in Caco-2 cells. Methods The change in the fluorescence of residual rhodamine 123 at the apical and central regions of Caco-2 cells was measured in the presence of digoxin or St John's wort by using time-lapse confocal laser scanning microscopy. The data were compared with measurements made using conventional techniques, a fluorescence microplate reader and a fluorescence microscope. Key findings The percentage decrease of rhodamine 123 caused by 10 µm digoxin or 0.1 µg/ml St John's wort was significantly larger in the apical region of the Caco-2 cell than in the central region or in the whole cell. The digoxin-induced inhibition in the apical region as measured by time-lapse confocal laser scanning microscopy was greater than that measured in the whole cell by a microplate reader or a fluorescence microscope. Conclusions The assay of residual rhodamine 123 in the apical region of Caco-2 cells by confocal laser scanning microscopy was more sensitive than the conventional methods using a microplate reader or fluorescence microscopy. It will be a valuable screening tool for studying both the inhibition and induction of P-glycoprotein activity.

Panax notoginseng saponins (PNS) are major components of Panax notoginseng, a herb with established clinical efficacy against vascular diseases. SHRSP.Z-Lepr(fa) /IzmDmcr (SHRSP.ZF) rats, a new animal model for metabolic syndrome, display an impaired vasorelaxation response in aortas and mesenteric arteries that is mediated by nitric oxide (NO). This study investigated whether PNS and its components can ameliorate this vascular dysfunction in SHRSP.ZF rats. In an in vitro study, in the presence or absence of PNS and its components, vasodilation in response to nitroprusside was determined from myographs under isometric tension conditions in aortas and mesenteric arteries from male SHRSP.ZF rats at 18-20 weeks of age. In an in vivo study, PNS (30 mg/kg per day) was orally administered to SHRSP.ZF rats from 8 to 20 weeks of age. In vitro treatment with PNS and Ginsenoside Rb1 increased nitroprusside-induced relaxation of aortas and mesenteric arteries in SHRSP.ZF rats. The PNS-induced increase was not affected by a nitric oxide (NO) synthase inhibitor or endothelium denudation. Relaxation in response to a cell-permeable cGMP analogue was increased by PNS, but cGMP accumulation by nitroprusside was not altered. In vivo treatment with PNS in SHRSP.ZF rats lowered blood pressure and increased relaxation and the expression of soluble guanylyl cyclase protein in arteries, without affecting metabolic abnormalities. These results indicate that PNS causes an increase in vasodilation in response to NO and a decrease in blood pressure, resulting in protection against vascular dysfunction in SHRSP.ZF rats. PNS might be beneficial in alleviating impaired vasodilation in metabolic syndrome.

The maternal environment during pregnancy and lactation has important effects on the offspring’s cardiovascular system. For example, changes in offspring blood pressure and vascular structure have been reported to occur in response to a maternal high salt intake during pregnancy and lactation. However, it remains unclear whether a maternal high salt intake may affect cardiac function in offspring. We previously demonstrated that high salt diet causes aggravation of hypertension in young spontaneously hypertensive rats (SHR). Therefore, in the present study we investigated the influence of exposure to a maternal high salt diet during gestation and lactation on offspring cardiac function in SHR. SHR dams were fed either a high salt diet (4% NaCl) or a control (0.3% NaCl) diet. After weaning, the offspring were fed the control diet for 8 weeks. Systolic blood pressure and heart rate of the offspring were measured without heating using a photoplethysmographic tail-cuff system at 11 weeks of age. Indices of both left ventricular (LV) systolic and diastolic function (LV developed pressure [LVDP], and maximum rate of LV decline [-dP/dt]) and coronary flow were determined in 12 week old offspring using a Langendorff isolated perfused working heart system. Offspring of the high-salt diet-fed dams (High salt) had lower blood pressure, heart rate, and indices of both LV systolic and diastolic function, compared with offspring of the control diet-fed dams (control) (Fig.). There were no significant differences in coronary flow or heart weight between the two groups. These results suggest that a maternal high salt intake is a predisposing factor for disturbance of cardiac function in offspring.

The aim of this study was to evaluate the effects of the mitogen-activated protein kinase (MAPK) pathway inhibitors SB203580, CMPD-1, SB239063, SP600125, and FR180204 on the activity of P-glycoprotein (P-gp) and to assess whether the MAPK pathway affects P-gp directly. Changes in the fluorescence of residual rhodamine 123, a marker of P-gp activity, in the apical region of Caco-2 cells were measured in the presence of MAPK pathway inhibitors using time-lapse confocal laser scanning microscopy at 0, 10, 20, 30, and 60 min. Significant differences were observed between the fluorescence levels of control cells and cells treated with SB203580 for 20, 30, or 60 min. However, no significant change was observed in the residual rhodamine 123 fluorescence of cells treated with CMPD-1, SB239063, SP600125, or FR180204. Among the p38-MAPK pathway inhibitors investigated, CMPD-1 and SB239063 showed no detectable effect on the activity of P-gp. Further, JNK 1, 2, 3-MAPK pathway (SP600125) and ERK1/2 pathway (FR180204) inhibitors did not affect P-gp activity. However, SB203580 enhanced the transfer of rhodamine 123 across the apical cell membrane. Thus, SB203580 activated P-gp, although not through the p38-MAPK pathway. Importantly, the MAPK pathway did not affect P-gp activity shortly after treatment.

Aims High salt intake is an environmental factor that promotes increased blood pressure. We previously demonstrated that high salt diet causes aggravation of hypertension and impaired vasodilation in response to nitric oxide (NO) in young spontaneously hypertensive rats (SHR), which exhibit low sensitivity to salt in adulthood. Changes in offspring blood pressure and cardiovascular structures have been reported. However, it remains unclear to what extent a maternal high salt intake may affect cardiac and/or vascular function in offspring. Therefore, we investigated influence of exposure to a maternal high salt diet during gestation and lactation on offspring's cardiac and arterial functions in SHR. Main methods SHR dams were fed either a high salt diet or a control diet. After weaning, the offspring were fed the high salt diet or control diet for 8 weeks. Key findings Compared with offspring of control diet-fed dams, at 12 weeks of age, offspring of the high-salt diet-fed dams had lower blood pressure, heart rate, indices of both left ventricular systolic and diastolic function, and a decreased aortic vasodilation response to NO. Postnatal high salt intake did not affect blood pressure, vasodilatory response, or cardiac function in offspring of high-salt diet-fed dams. Neither maternal nor postnatal dietary salt altered levels of lipid peroxide, superoxide dismutase, or angiotensinogen mRNA in serum and ventricle of the offspring. Significance Exposure to high maternal dietary salt induces cardiac and vascular dysfunction in offspring. These results point to the possible importance of avoiding excess dietary salt during gestation and lactation.

Although hyperlipidemia, high blood pressure, and diabetes increase the risk of arteriosclerosis, it is not clear whether hyperuricemia increases the risk of arteriosclerosis or not. We examined the effects of uric acid and curative drugs for hyperuricemia on atherosclerosis-susceptible C57BL/6J apolipoprotein E-deficient (apoE(-/-)) mice. Male apoE(-/-) mice (age: 6 weeks) were fed a normal diet (normal diet group) or a uric acid-enriched diet. Mice fed the uric acid-enriched diet were divided into three groups and administered a drinking vehicle (high uric acid diet group), allopurinol (20 mg·kg(-1)·d(-1)), or benzbromarone (20 mg·kg(-1)·d(-1)) for 10 weeks. Serum uric acid concentrations were higher in the high uric acid diet group than in the normal diet group, and concentrations in the allopurinol and benzbromarone groups were lower than in the high uric acid diet group. Serum total cholesterol and triglyceride levels were lower in the allopurinol group than in the high uric acid diet group. Oxidative stress was lower in the benzbromarone group than in the high uric acid diet group. Atherosclerotic lesion areas were smaller in the allopurinol and benzbromarone groups than in the high uric acid diet group. Thus, hyperuricemia may not be an independent risk factor for arteriosclerosis; however, the administration of allopurinol and benzbromarone prevented the development of atherosclerosis in apoE(-/-) mice fed a uric acid-enriched diet. The anti-atherosclerotic effect was in part due to lower total cholesterol and oxidative stress in the serum. Other possible mechanisms underlying this effect should be investigated.

We established a highly sensitive method for evaluating P-glycoprotein activity in Caco-2 cells. Using time-lapse confocal laser-scanning microscopy, we measured the change in fluorescence of residual rhodamine 123 in Caco-2 cells. Horizontal fluorescence images of rhodamine 123 in the apical and central parts of these cells were captured for 90 min. A continuous and significant decrease in the fluorescent intensity of rhodamine 123 in the apical part of the Caco-2 cells occurred during the measurement period, while the decrease in the central part was mild. The decrease in rhodamine 123 intensity in the apical part of Caco-2 cells were abolished in the presence of 10 microM digoxin, but the decrease in the central part was not. The decrease in total rhodamine 123 over whole cells was no significant influence of digoxin was observed. This residual rhodamine 123 assay for evaluating P-glycoprotein in the apical part of Caco-2 cells imaged by confocal laser scanning microscopy is more sensitive than conventional methods and will be a valuable screening tool for studying both the inhibition and induction of P-glycoprotein activity and expression. This method may also be useful for predicting P-glycoprotein-mediated alterations in the intestinal absorption of drugs.