Hypoglycemic and antihyperglycemic effect of Brassica juncea diet and their effect on hepatic glycogen content and the key enzymes of carbohydrate metabolism

Plants in the form of food or other remedial forms have been used for the treatment of various human ailments. Diabetes is one such disorder in which various form of plants and herbal remedies have been tried. Brassica juncea (BJ) seeds (Rai) are consumed in India as a spice in various food items. Previous studies have shown the hypoglycemic effect of this plant in rats. The present study was undertaken to study the hypoglycemic and anti-hyperglycemic of various strengths (5, 10 and 15%) of BJ seed diet in alloxan and streptozotocin induced diabetes in albino rats. In addition, key enzymes of carbohydrate metabolism (glucokinase – EC 2.7.1.1, hexokinase – EC 2.7.1.1, and phosphofructokinase – EC 2.7.1.11) and hepatic glycogen content was also assessed to understand the mechanism of action. BJ diet (10 and 15%) showed significant anti-hyperglycemic effect in alloxan (35 mg/kg) but not in STZ (60 mg/kg) rats. It also failed to modulate the hepatic glycogen content and enzyme activities.     

<Emphasis Type=Italic>In vitro</Emphasis> shoot regeneration from cotyledonary node explants of a multipurpose leguminous tree <Emphasis Type=Italic>Pterocarpus marsupium</Emphasis> Roxb.

Summary A protocol has been developed for in vitro plant regeneration from cotyledonary nodes of Pterocarpus marsupium Roxb. Multiple shoots were induced from cotyledonary nodes derived from 20-d-old axenic seedlings grown on Murashige and Skoog (MS) medium containing 2.22–13.32 μM benzyladenine (BA) or 2.32–13.93 μM kinetin alone or in combination with 0.26 μM α-naphthaleneacetic acid (NAA). The highest frequency of responding explants (85%) and maximum number of shoots per explant (9.5) were obtained on MS medium supplemented with 4.44 μM BA and 0.26 μM NAA after 15 wk of culture. A proliferating shoot culture was established by repeatedly subculturing the orginal cotyledonary nodal explant on fresh medium after each harvest of the newly formed shoots. Nearly 30% of the shoots formed roots after being transferred to half-strength MS medium containing 9.84 μM indole-3-butyric acid after 25 d of culture. Fifty percent of shoots were also directly rooted as microcuttings on peat moss, soil, and compost mixture (1∶1∶1). About 52% plantlets rooted under ex vitro conditions were successfully acclimatized and established in pots.     

<Emphasis Type="Italic">In vitro</Emphasis> shoot regeneration from cotyledonary node explants of a multipurpose leguminous tree, <Emphasis Type="Italic">Pterocarpus marsupium</Emphasis> roxb

Summary A protocol has been developed for in vitro plant regeneration from cotyledonary nodes of Pterocarpus marsupium Roxb. Multiple shoots were induced from cotyledonary nodes derived from 20-d-old axenic seedlings grown on Murashige and Skoog (MS) medium containing 2.22–13.32 μM benzyladenine (BA) or 2.32–13.93 μM kinetin alone or in combination with 0.26 μM α-naphthaleneacetic acid (NAA). The highest frequency for shoot regeneration (85%) and maximum number of shoots per explant (9.5) were obtained on the medium supplemented with 4.44 μM BA and 0.26 μM NAA after 15 wk of culture. A proliferating shoot culture was established by repeatedly subculturing the original cotyledonary nodal explant on fresh medium after each harvest of the newly formed shoots. Nearly 30% of the shoots formed roots after being transferred to half-strength MS medium containing 9.84 μM indole-3-butyric acid (IBA) after 25 d of culture. Fifty percent of shoots were also directly rooted as microtuttings on a peat moss, soil, and compost mixture (1∶1∶1). About 52% of plantlets were successfully acclimatized and established in pots.     

Effect of cobalt on the liver glycogen content in the streptozotocin-induced diabetic rats

Cobalt decreases blood glucose in diabetic rats but the mechanisms involved are unclear. To determine the contribution of glycogen metabolism to glycemia-lowering effect, glycogen contents of liver and muscle in the streptozotocin-induced diabetic rats were determined. The liver glycogen was depleted in diabetic rats. But when cobalt was administered to the rats, the glycogen returned to the level of healthy rats, concomitantly with the decrease in blood glucose. The cobalt treatment had no effect on the muscle glycogen in the diabetic rats. The tissue-specific responses of glycogen metabolism suggest the involvement of suppressed glucagon signaling due to cobalt treatment.     

Fluxes of carbohydrate metabolism in ripening bananas

The major fluxes of carbohydrate metabolism were estimated during starch breakdown by ripening bananas (Musa cavendishii Lamb ex Paxton). Hands of bananas, untreated with ethylene, were allowed to ripen in the dark at 21° C. Production of CO₂ and the contents of starch, sucrose, glucose and fructose of intact fruit were determined for a period of 10 d that included the climacteric. The detailed distribution of label was determined after supplying the following to cores of pulp from climacteric fruit: [U-¹⁴C]-, [1-¹⁴C]-, [3,4-¹⁴C]-and [6-¹⁴C]glucose, [U-¹⁴C]glycerol, ¹⁴CO₂. The data obtained were used to estimate the following fluxes, values given as mol hexose · (g FW)^–1 · h^–1 in parenthesis: starch to hexose monophosphates (5.9) and vice versa (0.4); hexose monophosphates to sucrose (7.7); sucrose to hexose (4.7); hexose to hexose monophosphate (3.8); glycolysis (0.5–1.6); triose phosphate to hexose monophosphates (0.14); oxidative pentose-phosphate pathway (0.48); CO₂ fixation in the dark (0.005). These estimates are related to our understanding of carbohydrate metabolism during ripening.We both thank Mr Richard Trethewey for his constructive criticism: S.A.H. thanks the Managers of the Broodbank Fund for a fellowship.     

The effect of glucose on the control of carbohydrate metabolism in ripening bananas

The effect of exogenous glucose on the major fluxes of carbohydrate metabolism in cores of climacteric fruit of banana (Musa cavendishii Lamb ex Paxton) was determined with the intention of using the effects in the application of top-down metabolic control analysis. Hands of bananas, untreated with ethylene, were allowed to ripen in the dark at 21 °C. Cores were removed from climacteric fruit and incubated in 100 or 200 mM glucose for 4 or 6 h. The rates of starch breakdown, sucrose and fructose accumulation and CO₂ production were measured. The steady-state contents of hexose monophosphates, adenylates and pyruvate were determined. In addition, the detailed distribution of label was determined after supply of the following: [U-¹⁴C]-, [1-¹⁴C]-, [3,4¹⁴C]and [6-¹⁴C]glucose, and [U-¹⁴C]glycerol. The data were used to estimate the major fluxes of carbohydrate metabolism. Supply of exogenous glucose led to increases in the size of the hexose-monophosphate pools. There was a small stimulation of the rate of sugar synthesis and a major increase in the rate of starch synthesis. Starch breakdown was inhibited. Respiration responded to the demand for ATP by sugar synthesis. The effect of glucose on fluxes and metabolite pools is discussed in relation to our understanding of the control and regulation of carbohydrate metabolism in ripening fruit.Abbreviations Glc6P glucose-6-phosphate - Glc1P glucose-1-phosphate - Fru6P fructose-6-phosphate - AEC adenylate energy chargeWe thank Geest Foods Group, Great Dunmow, Essex, UK for giving us the bananas. SAH thanks the managers of the Broodbank Fund for a fellowship.     

Effect of prolonged restraint on glycogen content and activities of four enzymes of carbohydrate metabolism in the liver of rats

Triphasic changes in glycogen content and activities of four enzymes of carbohydrate metabolism (glucose-6-phosphatase, phosphoenolpyruvate carboxykinase, hexokinase, and glucose-6-phosphate dehydrogenase) were studied in the liver of male Wistar rats exposed to 1, 5, 10, 15, 20, 30, 45, 60, 70 and 90-day movement restrain in pencil cases. It was assumed that these three phases corresponded to the alarm, resistance and exhaustion stages of Selye's general adaptation syndrome. In hypokinetic rats, however, a transition of the alarm reaction to the resistance stage was registered later, and hepatic glycogen accumulation was reduced in comparison with the standard pattern observed in chronic stress.     

The effect of hypoxia on the control of carbohydrate metabolism in ripening bananas

The aim of this work was to determine the effects of hypoxia on the major fluxes of carbohydrate metabolism in climacteric fruit of banana (Musa cavendishii Lamb ex Paxton). Hands of bananas, untreated with ethylene, were allowed to ripen in air at 21°C in the dark. When the climacteric began, fruit were transferred to 15 or 10% oxygen and were analysed once the climacteric peak had been reached 8–12 h later. The rates of starch breakdown, sucrose, glucose and fructose accumulation, and CO₂ production were determined, as were the contents of hexose monophosphates, adenylates and pyruvate. In addition, the detailed distribution of label was determined after supplying [U-¹⁴C]-, [1-¹⁴C]-, [3,4-¹⁴C]- and [6-¹⁴C]glucose, and [U-¹⁴C]glycerol to cores of tissue under hypoxia. The data were used to estimate the major fluxes of carbohydrate metabolism. There was a reduction in the rate of respiration. The ATP/ADP ratio was unaffected but there was a significant increase in the content of AMP. In 15% oxygen only minor changes in fluxes were observed. In 10% oxygen starch breakdown was reduced and starch synthesis was not detected. The rate of sucrose synthesis decreased, as did the rate of re-entry of hexose sugars into the hexose monophosphate pool. There was a large increase in both the glycolytic flux and in the flux from triose phosphates to hexose monophosphates. It is argued that the increase in these fluxes is due to activation of pyrophosphate: fructose-6-phosphate 1-phosphotransferase, and that this enzyme has an important role in hypoxia. The results are discussed in relation to our understanding of the control of carbohydrate metabolism in hypoxia.Abbreviations Glc6P glucose-6-phosphate - Glc1P glucose-1-phosphate - Fru6P fructose-6-phosphate - PP_i inorganic pyro-phosphateWe thank Geest Foods Group, Great Dunmow, Essex, UK for giving us the bananas. S.A.H. thanks the managers of the Brood bank Fund for a fellowship.     

The impact of reduced vacuolar invertase activity on the photosynthetic and carbohydrate metabolism of tomato

The impact of reduced vacuolar invertase activity on photosynthetic and carbohydrate metabolism was examined in tomato (Solanum lycopersicon L.). The introduction of a co-suppression construct (derived from tomato vacuolar invertase cDNA) produced plants containing a range of vacuolar invertase activities. In the leaves of most transgenic plants from line INV-B, vacuolar invertase activity was below the level of detection, whereas leaves from line INV-A and untransformed wild-type plants showed considerable variation. Apoplasmic invertase activity was not affected by the co-suppression construct. It has been suggested that, in leaves, vacuolar invertase activity regulates sucrose content and its availability for export, such that in plants with high vacuolar invertase activity a futile cycle of sucrose synthesis and degradation takes place. In INV-B plants with no detectable leaf vacuolar invertase activity, sucrose accumulated to much higher levels than in wild-type plants, and hexoses were barely detectable. There was a clear threshold relationship between invertase activity and sucrose content, and a linear relationship with hexose content. From these data the following conclusions can be drawn. (i) In INV-B plants sucrose enters the vacuole where it accumulates as hydrolysis cannot take place. (ii) There was not an excess of vacuolar invertase activity in the vacuole; the rate of sucrose hydrolysis depended upon the concentration of the enzyme. (iii) The rate of import of sucrose into the vacuole is also important in determining the rate of sucrose hydrolysis. The starch content of leaves was not significantly different in any of the plants examined. In tomato plants grown at high irradiance there was no impact of vacuolar invertase activity on the rate of photosynthesis or growth. The impact of the cosuppression construct on root vacuolar invertase activity and carbohydrate metabolism was less marked.Abbreviations CaMV Cauliflower Mosaic Virus - WT wild type     

Nutrient and salt relations of <Emphasis Type="Italic">Pterocarpus officinalis</Emphasis> L. in coastal wetlands of the Caribbean: assessment through leaf and soil analyses

Pterocarpus officinalis L. is a dominant tree of freshwater coastal wetlands in the Caribbean and the Guiana regions. It is frequently associated with mangroves in areas with high rainfall and/or surface run-off. We hypothesized that P. officinalis is a freshwater swamp species that when occurring in association with mangroves occupies low-salinity soil microsites, or alternatively that it possesses mechanisms preventing accumulation of salt in photosynthetic tissues. To test this we compared the mineral composition of soils and leaves of several species in two Pterocarpus forests in Puerto Rico associated with coastal mangroves, Sabana Seca and Punta Viento. Results indicate that (1) Sabana Seca has low soil salinity values even in the P. officinalis and Laguncularia racemosa mixed zone. In Punta Viento, salinity in the mixed zone was higher than in the Pterocarpus forest, but much lower than in the mangrove area; (2) In both forests, leaves of P. officinalis showed much lower Na concentrations than mangrove species. The K/Na ratios were 16–20 times higher in P. officinalis, indicating preferential absorption of K against Na. The mangrove fern (Acrostichum aureum) growing side by side with P. officinalis and L. racemosa in Punta Viento also revealed high Na exclusion capacity. We found an asymmetric distribution of cations in the blade and rachis of the P. officinalis compound leaves in both sites. The rachis accumulates more Na and Ca, but less Mg than the leaf blade. This sequestration of Na in the rachis prevents salt damage of photosynthetic tissue in the leaf blade.     

Effect of garlic oil on the levels of various enzymes in the serum and tissue of streptozotocin diabetic rats

Levels of red cell, serum acid, and alkaline phosphatases, serum amylase, alanine and aspartate transferase and bilirubin were examined in streptozotocin-induced diabetic rats treated with garlic oil and compared with the corresponding levels in diabetic control rats, normal rats and normal rats on garlic oil. Values of tissue amylase and total protein were also assessed from the pancreas, liver, and kidney. Treatment of diabetic rats with garlic oil significantly decreased the red cell phosphatase (p<0.01), serum acid and alkaline phosphatase (p<0.001) when compared to diabetic control rats. Serum alanine and asparate transferases were significantly (p<0.001) decreased as well as serum amylase (p<0.002) in garlic oil treated diabetic rats as compared with diabetic control rats. When treated with garlic oil, however, diabetic and normal rats showed significant increase (p<0.05) in the amylase levels of the pancrease, liver, and kidney.     

Some effects of nitrogen-starvation on nitrogen and carbohydrate metabolism inAnkistrodesmus braunii

Enzymic activities have been measured in cell-free extracts from nitrogen-starved cultures ofAnkistrodesmus braunii. During ten hours of nitrogenstarvation the activities of the enzymes nitrite reductase (E.C.1.6.6.4), glutamic dehydrogenase (E.C.1.4.1.4), glutamine synthetase (E.C.6.3.1.2) and urea amidolyase (E.C.3.5.1.5) were derepressed while the activities of the enzymes malate dehydrogenase (E.C.1.1.1.37) and hexokinase (E.C.2.7.1.1) remained more or less unchanged. In contrast, the photosynthetic capacity of the nitrogen-starved cultures declined rapidly and accompanying this decline were losses in the activities of ribulose diphosphate carboxylase (E.C.4.1.1.39) and triose phosphate-NADP-dehydrogenase (E.C.1.2.1.13).     

Apparent induction of key enzymes of the glyoxylic acid cycle in senescent barley leaves

The activities of two key enzymes of the glyoxylic-acid cycle, isocitrate lyase and malate synthase, can barely be detected in mature, presenescent primary leaves of barley (Hordeum vulgare L.) but are apparently induced in senescent leaf tissue. Upon incubation of leaf segments in permanent darkness, the activities appear and increase dramatically up to the sixth day and thereafter decline. The glyoxylic-acid cycle may thus be functional during foliar senescence. The main period of galactolipid loss is characterized by RQ values as low as 0.63, indicating that long-chain fatty acids produced from thylakoidal acyl-lipids may be utilized for gluconeogenesis involving corresponding glyoxisomal metabolic pathways. Foliar senescence may be characterized by a peroxisomeglyoxysome transition analogous to the glyoxisome-peroxisome transition in greening cotyledons of fat-storing seeds.Abbreviations FW fresh weight - MGDG monogalactosyl diacylglycerol - RQ respiratory quotient     

Activity of enzymes of carbon metabolism during the induction of Crassulacean acid metabolism in Mesembryanthemum crystallinum L.

The maximum extractable activities of twenty-one photosynthetic and glycolytic enzymes were measured in mature leaves of Mesembryanthemum crystallinum plants, grown under a 12 h light 12 h dark photoperiod, exhibiting photosynthetic characteristics of either a C₃ or a Crassulacean acid metabolism (CAM) plant. Following the change from C₃ photosynthesis to CAM in response to an increase in the salinity of in the rooting medium from 100 mM to 400 mM NaCl, the activity of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) increased about 45-fold and the activities of NADP malic enzyme (EC 1.1.1.40) and NAD malic enzyme (EC 1.1.1.38) increased about 4- to 10-fold. Pyruvate, Pi dikinase (EC 2.7.9.1) was not detected in the non-CAM tissue but was present in the CAM tissue; PEP carboxykinase (EC 4.1.1.32) was detected in neither tissue. The induction of CAM was also accompanied by large increases in the activities of the glycolytic enzymes enolase (EC 4.2.1.11), phosphoglyceromutase (EC 2.7.5.3), phosphoglycerate kinase (EC 2.7.2.3), NAD glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12), and glucosephosphate isomerase (EC 2.6.1.2). There were 1.5- to 2-fold increases in the activities of NAD malate dehydrogenase (EC 1.1.1.37), alanine and aspartate aminotransferases (EC 2.6.1.2 and 2.6.1.1 respectively) and NADP glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13). The activities of ribulose-1,5-bisphosphate (RuBP) carboxylase (EC 4.1.1.39), fructose-1,6-bisphosphatase (EC 3.1.3.11), phosphofructokinase (EC 2.7.1.11), hexokinase (EC 2.7.1.2) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) remained relatively constant. NADP malate dehydrogenase (EC 1.1.1.82) activity exhibited two pH optima in the non-CAM tissue, one at pH 6.0 and a second at pH 8.0. The activity at pH 8.0 increased as CAM was induced. With the exceptions of hexokinase and glucose-6-phosphate dehydrogenase, the activities of all enzymes examined in extracts from M. crystallinum exhibiting CAM were equal to, or greater than, those required to sustain the maximum rates of carbon flow during acidification and deacidification observed in vivo. There was no day-night variation in the maximum extractable activities of phosphoenolpyruvate carboxylase, NADP malic enzyme, NAD malic enzyme, fructose-1,6-bisphosphatase and NADP malate dehydrogenase in leaves of M. crystallinum undergoing CAM.Abbreviations CAM Crassulacean acid metabolism - PEP phosphoenolpyruvate - RuBP ribulose-1,5-bisphosphate     

On the localization of enzymes related to flavonoid metabolism in sections and tissues of oat primary leaves

During growth of the primary leaves of Avena sativa L., the distribution of extractable L-phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) and chalcone-flavanone isomerase (CFI, EC 5.5.1.6) activities in distinct leaf sections (top section, medium section and meristematic basal section) and in the epidermal and mesophyll tissues were investigated in relation to C-glycosylflavone accumulation. Characteristic changes have been observed in the levels of PAL and CFI activities within the three leaf sections, depending upon their stage of development. An increase in both enzyme activities accompanies a strong flavone accumulation in the section of the leaf that derives from the basal meristem. Highest specific PAL activity is localized in the meristem itself, which is poor in both flavones and CFI activity. Total flavone accumulation was found to be nearly the same in all three leaf tissues, lower and upper epidermis and mesophyll. Similarly, PAL activity is distributed about equally in these tissues in young leaves; in older ones, activity is relatively higher in the lower leaf epidermis. In contrast, CFI is found to be localized almost entirely in the mesophyll and not in the epiderms. Therefore the question arises whether CFI is involved at all in flavone metabolism and whether it may represent, as a marker enzyme, the localization of other specific C₁₅-enzymes of the flavonoid biosynthetic pathway in oat primary leaves.Abbreviations PAL L-phenylalamine ammonia lyase - CFI chalcone-flavanone isomerase     

Effect of the aqueous extract of Hyptis pectinata on liver mitochondrial respiration

Some studies have indicated that mitochondria may be the target organelle of plants. We therefore decided to assess the effects of the aqueous extract of Hyptis pectinata leaves on liver mitochondrial respiratory function in vitro. Eight rat livers were subjected to isolation of mitochondria by differential centrifugation. In an adequate medium, the plant extract was added at different concentrations. The analyzed data were: state 3, state 4 and respiratory control ratio (RCR). H. pectinata extract caused a statistically significant decrease in state 3 (at 0.05, 0.1 and 0.2 mg/mg protein) and RCR (at 0.05, 0.1 and 0.2 mg/mg protein). Respiratory state 4 was not altered by the increasing concentrations. In conclusion, the aqueous extract of H. pectinata leaves may not injure the mitochondrial inner membrane but decreases significantly the oxidative phosphorylation.     

Phosphoribosyl pyrophosphate and the measurement on inorganic pyrophosphate in plant tissues

This work provides further evidence that plants contain appreciable amounts of inorganic pyrophosphate (PPi), and that breakdown of phosphoribosyl pyrophosphate (PPRibP) does not contribute significantly to the PPi detected in plant extracts. Inorganic pyrophosphate in extracts of the roots of Pisum sativum L., clubs of the spadices of Arum maculatum L., and the developing endosperm of Zea mays L. was assayed with pyrophosphate fructose 6-phosphate 1-phosphotransferase (EC 2.7.1.90), and with sulphate adenyltransferase (EC 2.7.7.4). The two different assays gave the same value for PPi content, and for recovery of added PPi. It was shown that PPRibP is converted to PPi during the extraction of PPi. However, the amounts of PPRibP in clubs of A. maculatum and the developing endosperm of Z. mays were negligible in comparison with the contents of PPi.Abbreviations EDTA ethylenediaminetetraacetic acid - PFK(PPi) pyrophosphate fructose 6-phosphate 1-phosphotransferase - PPi inorganic pyrophosphate - PPRibP phosphoribosyl pyrophosphate     

Changes in the non-structural carbohydrate content of cotton (Gossypium spp.) fibres at different stages of development

The neutral sugars (glucose, fructose, and sucrose) and the sugar phosphates (glucose 6-phosphate, glucose 1-phosphate and fructose 6-phosphate) soluble in hot aqueous 80% methanol from the fibres of cotton — Gossypium arboreum L., G. barbadense L., and G. hirsutum L. — were determined at various stages of fibre development. In addition, the (13)--D-glucan content was measured and in the case of G. arboreum the rate of (13)--D-glucan and cellulose synthesis was determined with [¹⁴C]sucrose as the precursor. For each of the species a similar chronology was obtained for the changes in content of the various non-structural carbohydrates. At the early stages of secondary wall formation, glucose and fructose exhibited a maximum which was closely followed by a maximum in the (13)--D-glucan content and in the sugar phosphates. On the other hand, the sucrose content increased regularly until fibre maturity. The rates of synthesis of (13)--D-glucan and of cellulose were highest following the maximum in the (13)--D-glucan content, when the latter was being depleted.Abbreviations DMSO dimethyl-sulphoxide - DPA days post anthesis - UDP-glucose uridinediphosphoglucose     

Effect of carbon source on enzymes involved in glycerol metabolism inNeurospora crassa

Specific activities of eight enzymes involved in glycerol metabolism were determined in crude extracts of three strains ofNeurospora crassa after growth on six different carbon sources. One of the strains was wild type, which grew poorly on glycerol as sole carbon source; the other two were mutant strains which were efficient glycerol utilizers. A possible basis for this greater effeciency of glycerol utilization was catabolite repression of glyceraldehyde kinase by glycerol in wild type, and two-fold higher glycerate kinase activity in the mutant strains after growth on glycerol, thus apparently allowing two routes for glyceraldehyde to enter the glycolytic pathway in the mutant strains but only one in wild type. The preferential entry of glyceraldehyde to the glycolytic pathway through glycerate was suggested by the lack of glyceraldehyde kinase in all three strains after growth on one or more of the carbon sources and the generally higher levels of aldehyde dehydrogenase and of glycerate kinase than of glyceraldehyde kinase.     

Effect of Stemona curtisii root extract on P-glycoprotein and MRP-1 function in multidrug-resistant cancer cells

Multidrug resistance (MDR) is the result of overexpression of membrane bound proteins that efflux chemotherapeutic drugs from the cells. Two proteins, P-glycoprotein (P-gp) and multidrug-resistance associated protein-1 (MRP-1) efflux chemotherapeutic agents out of the cancer cell that decrease intracellular drug accumulation, thereby decreasing the effectiveness of many chemotherapeutic agents. In the present study, the ethanolic extract of the roots of Stemona curtisii Hook. was tested for the potential ability to modulate the MDR phenotype and function of P-gp and MRP-1. The S. curtisii extract reversed the resistance to putative chemotherapeutic agents, including vinblastine, paclitaxel and colchicine of KB-V1 cells (MDR human cervical carcinoma with high P-gp expression) in a dose-dependent manner, but not in KB-3-1 cells (drug sensitive human cervical carcinoma, which lack P-gp expression). The root extract also increased the intracellular uptake and retention of (3)[H]-vinblastine in KB-V1 cells dose dependently. The extract did not influence MDR phenotype-mediated MRP-1 in MRP1-HEK293 (human embryonic kidney cells stably transfected with pcDNA3.1-MRP1-H10 which show high MRP-1 expression) and pcDNA3.1-HEK293 (wild type). In summary, the S. curtisii root extract modulated P-gp activity but not MRP-1 activity. The result obtained from this study strongly indicated that S. curtisii extract may play an important role as a P-gp modulator as used in vitro and may be effective in the treatment of multidrug-resistant cancers. The purified form of the active components of S. curtisii extract should be investigated in more details in order to explain the molecular mechanisms involved in P-gp modulation. This is the first report of new biological activity in this plant, which could be a potential source of a new chemosensitizer.