Concentrations Of Tolbutamide Research Articles

Extending the application potential of capillary electrophoresis/frontal analysis for drug-plasma protein studies by combining it with mass spectrometry detection.

CE/frontal analysis (CE/FA) is probably one of the most frequently used modes of CE for studying affinity interactions. It is typically performed with classic UV-Vis detection that suffers from low concentration sensitivity. To overcome this limitation, the applicability of CE/FA in combination with ESI-MS detection for the investigation of drug-HSA interactions was demonstrated. The developed new method combines the advantages of CE/FA, such as low sample consumption and no labeling or immobilization of interacting partners, with the benefits of MS detection, such as higher selectivity and sensitivity; moreover, it can be used for molecules lacking a fluorophore or chromophore. The binding parameters of tolbutamide (TL) and glimepiride (GLP), first- and second-generation antidiabetics that differ strongly in their solubility in aqueous solutions, were investigated by this CE/FA-MS method. This method, in contrast to the CE/FA method with the most commonly used UV-Vis detection, is more sensitive; an almost three times lower LOD was reached. The binding parameters of TL and GLP were investigated by this CE/FA-MS method and compared with the literature data. The binding constant value of TL obtained by UV-Vis detection was lower than the value obtained by the method hyphenated with MS detection, which is probably given by the influence of the ESI parameters on the stability of drug-HSA complex. In addition, the ratio of TL and HSA concentrations was divergent in both of the experimental approaches. Finally, it can be concluded that both detection methods have their strengths and weaknesses.

Dysregulation of Glucagon Secretion by Hyperglycemia-Induced Sodium-Dependent Reduction of ATP Production

SummaryDiabetes is a bihormonal disorder resulting from combined insulin and glucagon secretion defects. Mice lacking fumarase (Fh1) in their β cells (Fh1βKO mice) develop progressive hyperglycemia and dysregulated glucagon secretion similar to that seen in diabetic patients (too much at high glucose and too little at low glucose). The glucagon secretion defects are corrected by low concentrations of tolbutamide and prevented by the sodium-glucose transport (SGLT) inhibitor phlorizin. These data link hyperglycemia, intracellular Na+ accumulation, and acidification to impaired mitochondrial metabolism, reduced ATP production, and dysregulated glucagon secretion. Protein succination, reflecting reduced activity of fumarase, is observed in α cells from hyperglycemic Fh1βKO and β-V59M gain-of-function KATP channel mice, diabetic Goto-Kakizaki rats, and patients with type 2 diabetes. Succination is also observed in renal tubular cells and cardiomyocytes from hyperglycemic Fh1βKO mice, suggesting that the model can be extended to other SGLT-expressing cells and may explain part of the spectrum of diabetic complications.

Electrophysiological and neurochemical effects of antidiabetic sulphonylurea tolbutamide in the rat ventral tegmental area and prefrontal cortex

Tolbutamide is an orally administered sulphonylurea, used in the management of non‐insulin‐dependent diabetes mellitus. This class of drug acts on the sulphonyureas receptors(SUR) through blockage of ATP‐regulated K‐channels to release insulin. Some studies have revealed the presence of sulphonylureas binding sites in the substantia nigra. However, there is very little documented data about the presence of these receptors in the ventral tegmental area (VTA) and prefrontal cortex(PFC).Here, using in vivo extracellular single unit recordings, we have investigated the electrophysiological effects of acute intravenous administration of tolbutamide (20mg/kg) on VTA dopamine and PFC pyramidal neurons. We also examined in vitro the effects of this drug on dopamine transporter activity using striatum and tegmental synaptosomes.Adult Sprague Dawley rats were deeply anaesthetised with chloral hydrate (400mg/kg) and urethane (1.5 g/kg) and placed in a stereotaxic instrument for VTA dopamine/GABA and PFC pyramidal neurons recordings, respectively. Appropriately, blood level glucose was monitored with glucometer to avoid hypoglycermia followed by administration with 2ml/kg of 20% glucose subsequent to tolbutamide injection, when necessary. Furthermore, we studied tolbutamide(30μM) effects on striatal synaptosome preparation for dopamine transporter activity through in vitro [3H]‐dopamine radiometric uptake assay technique.In the VTA, administration of tolbutamide induced biphasic effects on the basal activity of most of the dopamine neurons tested: large inhibition (up to 100%) during a relatively short period (1–3 min), caused by hyperpolarisation, followed by a long‐lasting excitatory effect (40% of the baseline activity). Significant increased burst activity was also observed. This initial inhibitory effect was insensitive to a pre‐administration of the dopamine D2 antagonist(eticlopride100μg/kg). Interestingly, presumed GABAergic VTA neurons exhibit only a monophasic significant excitatory effect following tolbutamide administration. In the prefrontal cortex, tolbutamide also induced a monophasic excitatory effect in a dose dependent manner on most of the presumed pyramidal neurons tested. Neurochemical in vitro investigation revealed a statistically significant partial decrease (p<0.05) in specific dopamine synaptosomal uptake at relatively high concentration of tolbutamide (30 μM) an indication of possible direct modulation of dopamine turn‐over.In conclusion, tolbutamide induced a unique biphasic effect in the VTA dopamine neurons. The large but short lasting inhibitory effect is hypothesised to be mediated by GABA interneurons which are found to be immediately activated by the drug. Future works are needed to understand the function of this putative metabolic‐sensitive modulation of dopamine neuronal activity.Support or Funding InformationSelf funded international student, supported by the university bursary department.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

KATP channel inhibition blunts electromechanical decline during hypoxia in left ventricular working rabbit hearts

Heart function is critically dependent upon the balance of energy production and utilization. Sarcolemmal ATP-sensitive potassium channels (KATP channels) in cardiac myocytes adjust contractile function to compensate for the level of available energy. Understanding the activation of KATP channels in working myocardium during high-stress situations is crucial to the treatment of cardiovascular disease, especially ischaemic heart disease. Using a new optical mapping approach, we measured action potentials from the surface of excised contracting rabbit hearts to assess when sarcolemmal KATP channels were activated during physiologically relevant workloads and during gradual reductions in myocardial oxygenation. We demonstrate that left ventricular pressure is closely linked to KATP channel activation and that KATP channel inhibition with a low concentration of tolbutamide prevents electromechanical decline when oxygen availability is reduced. As a result, KATP channel inhibition probably exacerbates a mismatch between energy demand and energy production when myocardial oxygenation is low. Sarcolemmal ATP-sensitive potassium channel (KATP channel) activation in isolated cells is generally understood, although the relationship between myocardial oxygenation and KATP activation in excised working rabbit hearts remains unknown. We optically mapped action potentials (APs) in excised rabbit hearts to test the hypothesis that hypoxic changes would be more severe in left ventricular (LV) working hearts (LWHs) than Langendorff (LANG) perfused hearts. We further hypothesized that KATP inhibition would prevent those changes. Optical APs were mapped when measuring LV developed pressure (LVDP), coronary flow rate and oxygen consumption in LANG and LWHs. Hearts were paced to increase workload and perfusate was deoxygenated to study the effects of myocardial hypoxia. A subset of hearts was perfused with 1μm tolbutamide (TOLB) to identify the level of AP duration (APD) shortening attributed to KATP channel activation. During sinus rhythm, APD was shorter in LWHs compared to LANG hearts. APD in both LWHs and LANG hearts dropped steadily during deoxygenation. With TOLB, APDs in LWHs were longer at all workloads and APD reductions during deoxygenation were blunted in both LWHs and LANG hearts. At 50% perfusate oxygenation, APD and LVDP were significantly higher in LWHs perfused with TOLB (199±16ms; 92±5.3mmHg) than in LWHs without TOLB (109±14ms, P=0.005; 65±6.5mmHg, P=0.01). Our results indicate that KATP channels are activated to a greater extent in perfused hearts when the LV performs pressure-volume work. The results of the present study demonstrate the critical role of KATP channels in modulating myocardial function over a wide range of physiological conditions.

In vitro and in vivo characterization of 13 CYP2C9 allelic variants found in Chinese Han population.

Our previous study detected totally 35 CYP2C9 allelic variants in 2127 Chinese subjects, of whom 21 novel alleles were reported for the first time in Chinese populations. The aim of the present study was to characterize the 13 CYP2C9 allelic variants both in vitro and in vivo. Different types of CYP2C9 variants were highly expressed in COS-7 cells, and 50 μM tolbutamide was added as the probing substrate to evaluate their metabolic abilities in vitro. Subsequently, the concentrations of tolbutamide and its metabolite in the plasma and urine within individuals with different types of genotypes were determined by HPLC to evaluate the catalytic activity of the 13 mutant CYP2C9 proteins in vivo. Our results showed that compared with *1/*1 wild-type subjects, subjects with *1/*40 genotype showed increased oral clearance (CL/F), whereas individuals with *1/*3, *1/*13, *3/*3, *3/*13, *1/*16, *1/*19, *1/*34, *1/*42, *1/*45, *1/*46, and *1/*48 genotype exhibited significantly decreased CL/F, and those with *1/*27, *1/*29, *1/*40, and *1/*41 genotype presented similar CL/F value. When expressed in COS-7 cells, the CYP2C9 variants showed similar pattern to the results in clinical study. The study suggests that, besides two typical defective alleles, *3 and *13, seven CYP2C9 allelic variants (*16, *19, *34, *42, *45, *46, and *48) cause defective effects on the enzymatic activities both in vitro and in vivo. In clinic, patients with these defective alleles should be paid close attention to.

Enhanced Enzymatic Reactivity for Electrochemically Driven Drug Metabolism by Confining Cytochrome P450 Enzyme in TiO2Nanotube Arrays

Understanding the enzymatic reaction kinetics that occur within a confined space or interface is a significant challenge. Herein, a nanotube array enzymatic reactor (CYP2C9/Au/TNA) was constructed by electrostatically adsorbing enzyme on the inner wall of TiO2 nanotube arrays (TNAs). TNAs with different dimensions could be fabricated by the anodization of titanium foil through varying the anodization potential or time. The electrical conductivity of TNAs was improved by electrodepositing Au nanoparticles on the inner wall of TNAs. The cytochrome P450 2C9 enzyme (CYP2C9) was confined inside TNAs as a model. The enzymatic activity of CYP2C9 and tolbutamide metabolic yield could be effectively regulated by changing the nanotube diameter and length of TNAs. The enzymatic rate constant k(cat) and apparent Michaelis constant K(m)(app) were determined to be 9.89 s(-1) and 4.8 μM at the tube inner diameter of about 64 nm and length of 1.08 μm. The highest metabolic yield of tolbutamide reached 14.6%. Furthermore, the designed nanotube array enzymatic reactor could be also used in situ to monitor the tolbutamide concentration with sensitivity of 28.8 μA mM(-1) and detection limit of 0.52 μM. Therefore, the proposed nanotube array enzymatic reactor was a good vessel for studying enzyme biocatalysis and drug metabolism, and has potential applications including efficient biosensors and bioreactors for chemical synthesis.

Coleus forskohlii extract attenuates the hypoglycemic effect of tolbutamide in vivo via a hepatic cytochrome P450-mediated mechanism.

This in vivo study in rats evaluated whether Coleus forskohlii extract (CFE) taken orally interacted with tolbutamide, a hypoglycemic drug metabolized by CYP2C enzymes. Rats were fed 0%, 0.3%, 1% (w/w) CFE diet for 2 weeks, followed by 0% CFE diet for 1 day. They were then given 40 mg/kg tolbutamide by intragastric gavage. Blood glucose level was determined up to 6 h after tolbutamide administration. CFE treatment increased total CYP content and various CYP subtypes in the liver. In particular, increases in activity and protein expression were noted for the CYP2B, CYP2C, and CYP3A subtypes. CFE treatment dose-dependently attenuated both the hypoglycemic action of tolbutamide at 6 h and the plasma concentration of tolbutamide. The activity of (S)-warfarin 7-hydroxylase, a CYP2C enzyme was negatively correlated with plasma tolbutamide level, which also showed a negative correlation with the reduction of blood glucose level. These results indicate that CFE induced hepatic CYPs in rats and attenuated the hypoglycemic action of tolbutamide via a hepatic CYP2C-mediated mechanism.

Effects of Peritoneal Dialysis on Pharmacotherapy: A Deductive Pharmacokinetic-model Approach to Predict Drug Concentration Profiles in Plasma and Peritoneal Fluid

The aim of this study was to present a deductive compartment pharmacokinetic (PK) model to predict the concentration profiles of drugs in plasma and peritoneal fluid in peritoneal dialysis (PD) rats. PK parameters of model drugs in normal and experimentally induced acute renal failure (ARF) rats not undergoing PD were obtained inductively in a common regression manner with a two-compartment model. In PD normal and ARF rats, PK parameters relating to the transfer of drugs to the peritoneal dialysate and the progress of renal failure were deductively modified to simulate the drug concentration-time profiles in plasma and in the peritoneal fluid in PD rats. The deductively introduced modifiers were the volume of distribution in the peripheral compartment, plasma protein binding, and solvent movement factor to the peritoneal fluid. Predicted profiles of tolbutamide, propranolol and cefazolin in PD normal and ARF rats were compared with the corresponding observed data. This minimal deductive approach yielded satisfactory accuracy in the prediction of both the plasma and peritoneal fluid concentrations of tolbutamide and propranolol.

An Ethinyl Estradiol-Levonorgestrel Containing Oral Contraceptive Does Not Alter Cytochrome P4502C9 In Vivo Activity

Oral contraceptives have been in wide use for more than 50 years. Levonorgestrel, a commonly employed progestin component of combined oral contraceptives, was implicated in drug-drug interactions mediated via CYP2C9. Although in vitro studies refuted this interaction, there are no confirmatory in vivo studies. In the current study, we examined the phenotypic status of CYP2C9 using low-dose (125 mg) tolbutamide before and after oral contraceptive use in reproductive age women. Blood was collected 24 hours after the tolbutamide oral dose was administered, plasma was isolated, and tolbutamide concentration (C24) was measured using liquid chromatography-mass spectrometry. The natural logarithm of tolbutamide C24, a metric for CYP2C9 phenotype, was found to be equivalent (within 80%-125% equivalency boundaries) before and after oral contraceptive use. In conclusion, levonorgestrel-containing oral contraceptives, the most commonly used form of oral contraception, do not affect the status of the CYP2C9 enzyme. This suggests that it is safe to co-administer levonorgestrel-containing oral contraceptives and CYP2C9 substrates, which include a wide array of drugs.

Role of KATP Channels in Glucose-Regulated Glucagon Secretion and Impaired Counterregulation in Type 2 Diabetes

SummaryGlucagon, secreted by pancreatic islet α cells, is the principal hyperglycemic hormone. In diabetes, glucagon secretion is not suppressed at high glucose, exacerbating the consequences of insufficient insulin secretion, and is inadequate at low glucose, potentially leading to fatal hypoglycemia. The causal mechanisms remain unknown. Here we show that α cell KATP-channel activity is very low under hypoglycemic conditions and that hyperglycemia, via elevated intracellular ATP/ADP, leads to complete inhibition. This produces membrane depolarization and voltage-dependent inactivation of the Na+ channels involved in action potential firing that, via reduced action potential height and Ca2+ entry, suppresses glucagon secretion. Maneuvers that increase KATP channel activity, such as metabolic inhibition, mimic the glucagon secretory defects associated with diabetes. Low concentrations of the KATP channel blocker tolbutamide partially restore glucose-regulated glucagon secretion in islets from type 2 diabetic organ donors. These data suggest that impaired metabolic control of the KATP channels underlies the defective glucose regulation of glucagon secretion in type 2 diabetes.

Tolbutamide Controls Glucagon Release From Mouse Islets Differently Than Glucose

We evaluated the role of ATP-sensitive K+ (KATP) channels, somatostatin, and Zn2+ in the control of glucagon secretion from mouse islets. Switching from 1 to 7 mmol/L glucose inhibited glucagon release. Diazoxide did not reverse the glucagonostatic effect of glucose. Tolbutamide decreased glucagon secretion at 1 mmol/L glucose (G1) but stimulated it at 7 mmol/L glucose (G7). The reduced glucagon secretion produced by high concentrations of tolbutamide or diazoxide, or disruption of KATP channels (Sur1−/− mice) at G1 could be inhibited further by G7. Removal of the somatostatin paracrine influence (Sst−/− mice or pretreatement with pertussis toxin) strongly increased glucagon release, did not prevent the glucagonostatic effect of G7, and unmasked a marked glucagonotropic effect of tolbutamide. Glucose inhibited glucagon release in the absence of functional KATP channels and somatostatin signaling. Knockout of the Zn2+ transporter ZnT8 (ZnT8−/− mice) did not prevent the glucagonostatic effect of glucose. In conclusion, glucose can inhibit glucagon release independently of Zn2+, KATP channels, and somatostatin. Closure of KATP channels controls glucagon secretion by two mechanisms, a direct stimulation of α-cells and an indirect inhibition via somatostatin released from δ-cells. The net effect on glucagon release results from a balance between both effects.

Evaluation of the pharmacokinetic interaction between ticagrelor and tolbutamide, a cytochrome P450 2C9 substrate, in healthy volunteers

To assess the effect of ticagrelor on the pharmacokinetics of tolbutamide (a CYP2C9 substrate), and the effect of tolbutamide on ticagrelor pharmacokinetics. In this randomized, double-blind, two-period, crossover study, 23 healthy volunteers received either placebo or ticagrelor 180 mg twice daily (b.i.d.) for 9 days, with a single open-label oral dose of tolbutamide 500 mg on Day 5. After washout (14 days), volunteers received the alternate treatment. Plasma concentrations of tolbutamide, 4-hydroxytolbutamide, ticagrelor, and AR-C124910XX were determined for pharmacokinetic analyses. Ticagrelor had no effect on tolbutamide or 4-hydroxytolbutamide pharmacokinetic parameters. The geometric least square mean ratios for maximum plasma concentration (Cmax) and area under the plasma concentration-time curve from Time 0 to infinity (AUC0-∞) were lose to unity, and the 90% confidence intervals (CI) were within the range 0.80 - 1.25 for both tolbutamide and 4-hydroxytolbutamide. The terminal elimination half-life (t1/2), and time to maximal plasma concentrations (tmax) for tolbutamide and its metabolite were unaffected by ticagrelor coadministration. Tolbutamide had no effect on the Cmax, area under the concentration curve over the 2-hour dosing interval (AUC0-τ), t1/2 or tmax of either ticagrelor or AR-C124910XX. Coadministration of ticagrelor and tolbutamide was well tolerated. These results suggest that ticagrelor does not affect tolbutamide metabolism and is therefore unlikely to affect CYP2C9-mediated metabolism of drugs.

Effects of Bu-Zhong-Yi-Qi-Tang on hepatic drug-metabolizing enzymes and plasma tolbutamide concentration in rats

Ethnopharmacological relevanceBu-Zhong-Yi-Qi-Tang (BT) is the dry powder derived from the aqueous extract of a mixture of 10 medicinal herbs. It is a traditional Chinese medicine being used for the treatment of various immune-related diseases. Aim of the studyTo investigate the effect of BT on hepatic drug-metabolizing enzymes and its effect on plasma concentrations of tolbutamide, a substrate of CYP2C, in rats. Materials and methods: Exp 1Thirty-two male Wistar rats were divided into four groups. Rats were fed a control diet and a control diet containing 1, 2.5 and 5% (w/w) of BT, respectively, for eight weeks. The activities of the major CYP and Phase II conjugating enzymes in rat liver microsomes as well as the antioxidant system in rat liver were assessed. Exp 2: Male Wistar rats were fed a control diet or a control diet containing 2.5% of BT, respectively, for eight weeks. A single 20-mg/kg oral dose of tolbutamide was then administered to each rat. Plasma samples were collected from each rat at 0.5, 1, 2, 4 and 8h after dosing. The concentrations of tolbutamide and glucose level in plasma were determined by high-performance liquid chromatography-mass spectrometer (HPLC/MS) and enzymatic method, respectively. ResultsSignificant decrease in microsomal CYP2C-catalyzed diclofenac 4-hydroxylation in the liver of rats fed the BT diet was observed. Increased UDP-glucuronosyltransferase (UGT) and glutathione S-transferase (GST) activities were also observed in the liver of rats fed the diet containing 2.5 and 5% of BT. Immunoblot analyses also showed decreases of CYP2C11 proteins in the liver of BT fed rats. In addition, rats fed the 2.5% BT diet for eight weeks had no effects on the disposition of tolbutamide and reduction of glucose level in plasma after orally administered of tolbutamide. ConclusionsRats fed the BT diet for eight weeks may decrease CYP2C enzyme activity and protein expression and increase Phase II conjugating enzyme activities in liver. However, BT may not affect the disposition and efficacy of tolbutamide.

Effects of Ginkgo biloba extract on the pharmacokinetics and pharmacodynamics of tolbutamide in protein-restricted rats

Effects of repeated administration of Ginkgo biloba extract on pharmacokinetics and pharmacodynamics of tolbutamide were examined in rats fed a low-protein diet. Rats were given a low (7% casein) or control (20% casein) protein diet for 21 days and administered Ginkgo biloba extract (100mg/kg per day) for the last 5 days. Tolbutamide was co-administered on the last day. Blood glucose and plasma tolbutamide concentrations were determined over the subsequent 12h and the activity of hepatic cytochrome P450s were determined at 12h after dosing. There were significant decreases in body weight, the ratio of liver to body weight, and plasma albumin concentrations in rats on the low-protein diet compared with controls. The hypoglycaemic effect of tolbutamide was significantly greater and the concentration of the drug in plasma was higher in the former group. The repeated administration of Ginkgo biloba extract had little influence on the hypoglycaemic effect of tolbutamide, but tended to decrease the drug concentration in plasma of control rats, while it reduced significantly the hypoglycaemic action and plasma concentration of tolbutamide in the protein-restricted rats. The effects of Ginkgo biloba extract on the pharmacokinetics and pharmacodynamics of tolbutamide were significantly enhanced in rats on the low-protein diet.

Studying significance of apoptosis in mediating tolbutamide‐induced teratogenesis in vitro

The incidence of type 2 diabetes mellitus (non-insulin-dependent diabetes mellitus) is growing worldwide and poses a serious public health problem in a current paradigm of changing life style and food habits. Tolbutamide (sulfonylurea) is among the commonly used anti-diabetic drugs worldwide for treating type 2 diabetes and is known to cause congenital malformations in animals. In this study, the effect of tolbutamide on major organogenesis period and the possible involvement of apoptosis in mediating congenital malformations have been carried out. In the present study design, post-implantation rat embryos of day 11 were cultured for 24 h with various concentrations of tolbutamide, i.e., 10, 100, and 1000 μg/mL cultures, respectively. The growth and developmental of each embryo was evaluated and compared with control ones for the presence of any malformations. The tolbutamide decreased all growth and developmental parameters in a concentration-dependent manner, when compared with control. However, exposure to tolbutamide at 10 μg/mL culture did not show any significant effect on embryonic growth and development in vitro. In parallel to this, flow cytometric analysis (cell cycle and annexin V binding) and DNA fragmentation assay were carried out followed by quantitation by 3'-OH labeling of cultured rat embryos to examine the role of apoptosis in bringing about tolbutamide-induced teratogenesis. All results were found to be dose dependent and an increase in apoptosis in embryonic tissues may be related to the increased risk of congenital malformations. The outcome of the research suggested that apoptosis might be involved in mediating teratogenesis of tolbutamide in vitro. Further research is warranted to fully understand this mechanism.

Effects of Sho-saiko-to on the pharmacokinetics and pharmacodynamics of tolbutamide in rats.

Although Sho-saiko-to (Xiao Chai Hu Tang), a major Chinese traditional medicine, is frequently prescribed with other synthetic or biotechnological drugs for the treatment of various chronic diseases, there is a dearth of information about interactions between sho-saiko-to and co-administered drugs. This paper reports the effects of Sho-saiko-to on the pharmacokinetics and glucose responses of a sulphonylurea hypoglycaemic agent, tolbutamide, after their oral administration in rats. After oral administration of tolbutamide (50 mg kg(-1)) with or without Sho-saiko-to extract powder (300 mg kg(-1)) to male Sprague-Dawley rats cannulated in the jugular vein, plasma tolbutamide and glucose levels were periodically measured. Co-administration of Sho-saiko-to tended to elevate the plasma tolbutamide concentration in the absorption phase. A two-compartment lag-time model was found to describe the plasma tolbutamide concentration-time data. The maximum concentration of tolbutamide was significantly increased and time to reach the maximum concentration was reduced to about 70% by co-administration with Sho-saiko-to. There was no significant change in area under the curve or in the elimination half-life of tolbutamide. The extent of the lowering effect of tolbutamide on plasma glucose levels was increased up to 0.75 h and decreased after 5 h after co-administration of Sho-saiko-to. In conclusion, these studies suggest that sho-saiko-to slightly hastens the gastrointestinal absorption of tolbutamide. Furthermore, it is considered that elevation of the gastrointestinal absorption rate by Sho-saiko-to might potentiate the hypoglycaemic effect of this sulphonylurea in the early period after oral administration.

Oral hypoglycaemic, antihyperglycaemic and antidiabetic activities of Sri Lankan Broken Orange Pekoe Fannings (BOPF) grade black tea (Camellia sinensis L.) in rats

ETHNOPHARMCOLOGICAL RELEVANCE: Sri Lankan traditional practitioners recommend the consumption of black tea infusion (BTI) made from Camellia sinensis L. plant for regulation of glycaemia. However, they do not specify the grade of tea and their origin (i.e., agroclimatic elevation) and as such many prediabetics and milddiabetics use BOPF grade tea. This study examines the blood glucose lowering potential of Sri Lankan BOPF grade tea and its potency with respect to agroclimatic elevations. Unblended orthodox BOPF grade tea samples were collected from high-, mid- and low-grown agroclimatic elevations in Sri Lanka. Different concentrations of warm BTI (60, 120 and 480 mg/ml), tolbutamide (reference drug: 22.5mg/kg body weight) and water (control) were orally administered to different groups of rats, and hypoglycaemic and antihyperglycaemic activities were assessed. Antidiabetic activity was determined using streptozotocin induced diabetic rats. Mechanisms of blood glucose lowering actions were investigated using several standards techniques. BTI exhibited significant (P<0.05), dose-dependent and marked hypoglycaemic and antihyperglycaemic activities with quick onset. These effects did not differ with respect to agroclimatic elevation, although there were differences in the content of phyto-constituents. BTI also showed marked and quick antidiabetic activity. BTI inhibited intestinal glucose absorption and impaired α-glucosidase and α-amylase activities. BTI possessed insulinomimetic action, ability to improve insulin sensitivity and in vivo antioxidant activity. Notably, BTI was nontoxic. BTI of Sri Lankan BOPF grade tea has oral hypoglycaemic, antihyperglycaemic and antidiabetic actions which are mediated via multiple mechanisms. This study also indicates that, BOPF grade tea of any agroclimatic elevations in Sri Lanka could be used in the regulation of glycaemia.

Chronopharmacological Assessment Identified GLUT4 as a Factor Responsible for the Circadian Variation of the Hypoglycemic Effect of Tolbutamide in Rats

The circadian relationship between the pharmacokinetics and pharmacodynamics of tolbutamide in rats was analyzed using a compartment model. The basal concentration of plasma glucose had a circadian rhythm with the acrophase at 15:19 h. After intravenous administration of tolbutamide at 06:00, 14:00, or 18:00 h, the hypoglycemic effect showed a circadian variation, with the greatest effect at 18:00 h and the lowest effect at 06:00 h. The time courses of unbound tolbutamide concentration in plasma after intravenous administration were predicted using the model-estimated total concentration of tolbutamide and the albumin concentration and resulted in profiles that did not vary with the time of administration. Significant low insulin resistance was observed at 18:00 h to i.v. glucose and insulin loads. There was no obvious time dependency in the expression of glucose transporter 4 (GLUT4) in epididymal adipocytes. The hypoglycemic rate estimated from the plasma glucose concentration was described by the conventional pharmacokinetic-pharmacodynamic model with an effect compartment. The time courses of theoretical signals in the effect compartment described the observed circadian changes in the increased expression profile of GLUT4 normalized by the increased plasma insulin (IRI) concentration (ΔGLUT4/ΔIRI) after dosing. Thus, the time dependency in glucose uptake is responsible for the circadian variation of the hypoglycemic effect of tolbutamide.

Gap junctions and memory: An investigation using a single trial discrimination avoidance task for the neonate chick

Gap junctions are important to how the brain functions but are relatively under-investigated with respect to their contribution towards behaviour. In the present study a single trial discrimination avoidance task was used to investigate the effect of the gap junction inhibitor 18-α-glycyrrhetinic acid (αGA) on retention. Past studies within our research group have implied a potential role for gap junctions during the short-term memory (STM) stage which decays by 15 min post-training. A retention function study comparing 10 μM αGA and vehicle given immediately post-training demonstrated a significant main effect for drug with retention loss at all times of test (10–180 min post-training). Given that the most common gap junction in the brain is that forming the astrocytic network it is reasonable to conclude that αGA was acting upon these. To confirm this finding and interpretation two additional investigations were undertaken using endothelin-1 (ET-1) and ET-1 + tolbutamide. Importantly, a retention function study using 10 nM ET-1 replicated the retention loss observed for αGA. In order to confirm that ET-1 was acting on astrocytic gap junctions the amnestic action of ET-1 was effectively challenged with increasing concentrations of tolbutamide. The present findings suggest that astrocytic gap junctions are important for memory processing.

Interactions Between Herbal Medicines and Prescribed Drugs

The concomitant use of herbal medicines and pharmacotherapy is wide spread. We have reviewed the literature to determine the possible interactions between seven popular herbal medicines (ginkgo, St John's wort, ginseng, garlic, echinacea, saw palmetto and kava) and conventional drugs. Literature searches were performed using MEDLINE, Cochrane Library and EMBASE and we identified 128 case reports or case series, and 80 clinical trials. Clinical trials indicate that St John's wort (Hypericum perforatum), via cytochrome P450 (CYP) and/or P-glycoprotein induction, reduces the plasma concentrations (and/or increases the clearance) of alprazolam, amitriptyline, atorvastatin, chlorzoxazone, ciclosporin, debrisoquine, digoxin, erythromycin, fexofenadine, gliclazide, imatinib, indinavir, irinotecan, ivabradine, mephenytoin, methadone, midazolam, nifedipine, omeprazole, oral contraceptives, quazepam, simvastatin, tacrolimus, talinolol, verapamil, voriconazole and warfarin. Case reports or case series suggest interactions of St John's wort with adrenergic vasopressors, anaesthetics, bupropion, buspirone, ciclosporin, eletriptan, loperamide, nefazodone, nevirapine, oral contraceptives, paroxetine, phenprocoumon, prednisone, sertraline, tacrolimus, theophylline, tibolone, tryptophan, venlafaxine and warfarin. Ginkgo (Ginkgo biloba) decreases the plasma concentrations of omeprazole, ritonavir and tolbutamide. Clinical cases indicate interactions of ginkgo with antiepileptics, aspirin (acetylsalicylic acid), diuretics, ibuprofen, risperidone, rofecoxib, trazodone and warfarin. Ginseng (Panax ginseng) may interact with phenelzine and warfarin. Kava (Piper methysticum) increases the clearance of chlorzoxazone (a CYP2E1 substrate) and may interact with alprazolam, levodopa and paroxetine. Garlic (Allium sativum) interacts with chlorpropamide, fluindione, ritonavir and warfarin; it also reduces plasma concentrations of chlorzoxazone (a CYP2E1 probe). Echinacea might affect the clearance of caffeine (a CYP1A2 probe) and midazolam (a CYP3A4 probe). No interactions have been reported for saw palmetto (Serenoa repens). Numerous interactions between herbal medicines and conventional drugs have been documented. While the significance of many interactions is uncertain, several interactions, particularly those with St John's wort, may have serious clinical consequences.