[Quantitative analysis of Danshensu in Tongmai Oral Solution by HPLC]

OBJECTIVE

To establish a method by RP-HPLC for determination of content of Danshensu (3,4-hydroxybenzyl lacticacid) in Tongmai Oral Solution.

METHODS

The samples were separated on an ODS column Hypersil C18 (10 microm, 4.6 mm x 200 mm) with the mobile phase 0. 5% acetic acid-methanol-dimethyl formamide (99:0.5:0.5). The flow rate was 1.2 ml/min, and the detection wavelength was set at 335nm.

RESULTS

The average recovery of Danshensu was 98.31%, and RSD was 2. 11%.

CONCLUSION

The method is efficient and accurate with a good repeatability and can be used for the quality control of Tongmai Oral Solution.

Protective effects of Danshensu from the aqueous extract of Salvia miltiorrhiza (Danshen) against homocysteine-induced endothelial dysfunction

Homocysteine (Hcy) is a by-product of methionine metabolism. An imbalance of Hcy in the body may lead to hyperhomocysteinemia, a condition with elevated Hcy concentration in blood that may be one of the risk factors responsible for the development of several vascular diseases (thromboembolism, atherosclerosis, stroke, vascular diseases and dementia). Radix Salvia miltiorrhiza (Danshen), a well-known Chinese medicinal herb that can activate and improve blood microcirculation, is noticeable for its beneficial effect in treating cardiovascular diseases. The present study is to demonstrate the protective effect of Danshen extract against the homocysteine-induced adverse effect on human umbilical vein endothelial cell (HUVEC). Homocysteine (5 mM) not only decreased the cell viability but also caused the disruption of capillary-like structure formation in vitro. The protective effect of Danshen aqueous extract and its active compounds on endothelial cell function were demonstrated through an in vitro tube formation assay, which mimics the new blood vessel formation. To identify the active components in the aqueous extract of Danshen, the content was characterized by instrumental analysis using high performance liquid chromatography with diode array detector (DAD) and electrospray tandem mass spectrometry (ESI-MS/MS). Interestingly, Danshen extract and its pure compounds showed different effectiveness in protecting HUVEC against Hcy-induced injury according to the following descending order: Danshen aqueous extract, 3-(3,4-dihydroxy-phenyl)-2-hydroxy-propionic acid (Danshensu), protocatechuic acid, catechin and protocatechualdehyde. We believed that such findings might provide evidence in understanding the beneficial effects of Danshen on the cardiovascular system.

Metabolic studies on the total phenolic acids from the roots ofSalvia miltiorrhiza in rats

Phenolic acids are the main active constituents of Salvia miltiorrhiza Bunge. The metabolism of total phenolic acids from the roots of Salvia miltiorrhiza in rats was investigated. A sample preparation method combining the solid-phase extraction with liquid-liquid extraction was established to separate metabolites from the biological matrix. HPLC-UV and HPLC-MS methods were employed to analyze the metabolites. Five metabolites (M1-M5) were identified by HPLC-MS analysis and comparison with those of the reference standards. The fi ve metabolites were characterized as danshensu (M1), caffeic acid (M2), ferulic acid (M3), isoferulic acid (M4) and methylized ferulic acid (M5), respectively. The possible metabolic pathway of the phenolic acids is proposed.

[Effect of danshensu, protocatechualdehyde and danshen injection on calcium ion concentration in cytoplasm of human erythrocytes]

OBJECTIVE

To study the predominant calcium-antagonist components of Danshen injection.

METHOD

The effects of danshensu, protocatechualdehyde and Danshen injection on calcium concentration in cytoplasm of erythrocytes were examined in vitro by the fluorescent Ca+ -chelator fura-2.

RESULT

Either DS182 or PCAD can decrease in dose-dependent cytosolic free calcium concentration in human erythrocytes. They had additive effect when mixed, which was similar to Danshen injection.

CONCLUSION

DS182 and PCAD may be predominant calcium-antagonist components of Danshen injection.

[Study on adsorption of danshen water-soluble compounds with macroporous resin D301]

OBJECTIVE

To study the adsorption and enrichment of effective compounds of danshensu, and protocatechualdehyde from Danshen water extracts by macroporous resin D301.

METHOD

The change of active compounds was observed by detecting the amount of danshensu and protocatechualdehyde with HPLC.

RESULT AND CONCLUSION

Macroporous resins D301 can be used in the process of adsorbing and purifying active compounds of danshensu and protocatechualdehyde, and increase the amount of active compounds in water extracts.

Preparation and characterization of poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (PLA-PEG-PLA) microspheres for controlled release of paclitaxel

Microspheres of a new kind of copolymer, poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (PLA-PEG-PLA), are proposed in the present work for clinical administration of an antineoplastic drug paclitaxel with hypothesis that incorporation of a hydrophilic PEG segment within the hydrophobic PLA might facilitate the paclitaxel release. Paclitaxel-loaded PLA-PEG-PLA microspheres of various compositions were prepared by the solvent extraction/evaporation method. Characterization of the microspheres was then followed to examine the particle size and size distribution, the drug encapsulation efficiency, the colloidal stability, the surface chemistry, the surface and internal morphology, the drug physical state and its in vitro release behavior. The effects of polymer types, solvents and drug loading were investigated. It was found that in the microspheres the PEG segment was homogeneously distributed and caused porosity. Significantly faster release from PLA-PEG-PLA microspheres resulted in comparison with the PLGA counterpart. Incorporation of water-soluble solvent acetone in the organic solvent phase further increased the porosity of the PLA-PEG-PLA microspheres and facilitated the drug release. A total of 49.6% sustained release of paclitaxel within 1 month was achieved. Potentially, the presence of PEG on the surface of PLA-PEG-PLA microspheres could improve their biocompatibility. PLA-PEG-PLA microspheres could thus be promising for the clinical administration of highly hydrophobic antineoplastic drugs such as paclitaxel.

[Salvianolic acid A inhibits nucleoside transport and potentiates the antitumor activity of chemotherapeutic drugs]

AIM

To investigate the inhibitory activity of salvianolic acid A (SAA) on nucleoside transport in cancer cells and its antitumor effect.

METHODS

[3H] thymidine and [3H] uridine transport assays were used to determine the inhibitory activity on nucleoside transport in Ehrlich carcinoma cells. The cytotoxicity to cultured cancer cells was examined with clonogenic assay. The antitumor effect in vivo was evaluated with transplantable tumor model in mice.

RESULTS

SAA was shown to inhibit thymidine and uridine transport in Ehrlich carcinoma cells with IC50 values of 18.1 and 17.1 micromol x L(-1), respectively. By clonogenic assay, the IC50 of SAA for KB cells was 44.7 micromol x L(-1). SAA markedly potentiated the cytotoxicity of 5-FU and mitomycin C in KB cells as well as the cytotoxicity of MTX in human hepatoma BEL-7402 cells. For in vivo experiment, sarcoma 180 cells were transplanted sc in mice and tested drugs were administered ip. When administered separately, SAA at 200 mg x kg(-1) and 5-FU at 10 mg x kg(-1) inhibited tumor growth by 41% and 27%, respectively. Combination of the two drugs inhibited tumor growth by 63% (CDI = 0.86).

CONCLUSION

SAA is active in blocking nucleoside transport in cancer cells and potentiates the cytotoxicity of chemotherapeutic drugs. As an agent showing moderate antitumor effect in vivo, SAA might be useful in combination cancer therapy.

Recovery of Ammonium Lactate and Removal of Hardness from Fermentation Broth by Nanofiltration

Nanofiltration (NF) was investigated as an alternative to desalting electrodialysis (ED) and ion exchange for the recovery of ammonium lactate from fermentation broth. Three commercial NF membranes, NF45, NF70, and NTR-729HF, were characterized with 50 mM NaCl, MgSO(4), and glucose solutions. NF45 membrane was selected because it showed the lowest rejection of monovalent ion, the highest rejection of divalent ion, and the highest rejection of nonpolar molecule. Effects of the operating pressure were investigated in a range of 100-400 psig, on the flux, lactate recovery, and glucose and magnesium removal from a real fermentation broth containing about 1.0 M of ammonium lactate. The flux and recovery rate increased linearly with the pressure. However, lactate rejection also increased with the pressure, lowering the recovery yield. More magnesium ions and glucose were rejected as the pressure was increased, and at 400 psig, for example, magnesium ion was almost completely rejected, highlighting the chance of obviating the necessity of ion exchange to remove hardness, by using NF instead of desalting ED. Membrane fouling was not so severe as expected, considering the complex nature and a rather high concentration of the fermentation broth treated.

Lactobacillus plantarum MiLAB 393 produces the antifungal cyclic dipeptides cyclo(L-Phe-L-Pro) and cyclo(L-Phe-trans-4-OH-L-Pro) and 3-phenyllactic acid

We have isolated a Lactobacillus plantarum strain (MiLAB 393) from grass silage that produces broad-spectrum antifungal compounds, active against food- and feed-borne filamentous fungi and yeasts in a dual-culture agar plate assay. Fusarium sporotrichioides and Aspergillus fumigatus were the most sensitive among the molds, and Kluyveromyces marxianus was the most sensitive yeast species. No inhibitory activity could be detected against the mold Penicillium roqueforti or the yeast Zygosaccharomyces bailii. An isolation procedure, employing a microtiter well spore germination bioassay, was devised to isolate active compounds from culture filtrate. Cell-free supernatant was fractionated on a C(18) SPE column, and the 95% aqueous acetonitrile fraction was further separated on a preparative HPLC C(18) column. Fractions active in the bioassay were then fractionated on a porous graphitic carbon column. The structures of the antifungal compounds cyclo(L-Phe-L-Pro), cyclo(L-Phe-trans-4-OH-L-Pro) and 3-phenyllactic acid (L/D isomer ratio, 9:1), were determined by nuclear magnetic resonance spectroscopy, mass spectrometry, and gas chromatography. MIC values against A. fumigatus and P. roqueforti were 20 mg ml(-1) for cyclo(L-Phe-L-Pro) and 7.5 mg ml(-1) for phenyllactic acid. Combinations of the antifungal compounds revealed weak synergistic effects. The production of the antifungal cyclic dipeptides cyclo(L-Phe-L-Pro) and cyclo(L-Phe-trans-4-OH-L-Pro) by lactic acid bacteria is reported here for the first time.

[Studies on lipase-catalyzed synthesis of ethylglucoside lactate in non-aqueous phase]

Ethylglucoside lactate, a novel Alpha-Hydroxy Acids Derivative, was synthesized by transesterification in non-aqueous phase using immobilized lipase as biocatalyst. Based on the studies of the factors effecting initial rate and conversion under atmospheric pressure (solvent, acyl donor, different immobilized lipase, substrate concentration, enzyme concentration and temperature), the results show that solvent-free medium using butyllactate as acyl donor is suitable to the ester synthesis. The reaction conditions have been optimized as the following: the amount of enzyme = 75 g/L, the ethylglucoside concentration = 0.4 mol/L, 70 degrees C, 200 r/min, 50 h, which the conversion was 71%. A 90% conversion and a 60.7 mmol.L-1.h-1 initial rate can be obtained under reduced pressure, which the conditions are enzyme 75 g/L, ethylglucoside 0.35 mol/L, 65 degrees C, 200 r/min and 40 h. The product purified by extraction and SIO2 chromatography was identified by infrared spectroscopy and 1H NMR.

Determination of Danshensu, a major active compound of Radix Salvia miltiorrhiza in dog plasma by HPLC with fluorescence detection

A simple and sensitive high performance liquid chromatography method has been developed for the determination of Danshensu (3, 4-dihydroxyphenyllactic acid) in dog plasma. Plasma samples were extracted with ethyl acetate. Analysis of the extracts was performed on a reversed-phase column with an aqueous phosphate buffer-acetonitrile (93:7, v/v) mobile phase, and 4-hydroxybenzoic acid was used as the internal standard. Fluorescence detection at 285 nm (excitation) and 320 nm (emission) was employed. Standard curves were linear in the range from 0.125 to 11.3 microg/mL (regression coefficient r > 0.993) on three different days. Mean recovery was determined as 96.4% by analysis of plasma standard containing 0.63, 5.65 and 11.3 microg/mL of Danshensu. The inter-day precision (RSD) ranged from 3.4 to 8.6% at concentrations of 0.125, 1.88, 6.28 and 11.3 microg/mL, and the intra-day precision was better than 7.2%. The detection and quantitation limits were 0.063 and 0.125 microg/mL, respectively. This validated assay was applied to the determination of Danshensu concentration in dog plasma after oral administration of Radix Salvia miltiorrhiza extracts.

[Preparation and evaluation of in-situ synthesis zeolite gas-liquid modified columns]

A new kind of NaA zeolite column has been prepared by in-situ synthesis technique. In comparing with traditional coating method, the in-situ NaA zeolite carrier is much more uniform and rigid. Several kinds of zeolite gas-liquid modified columns have been prepared with this in-situ technology, which showed satisfactory features in separation property and thermal stability. The successful utilization of mini-length and wide-bore columns showed good practical prospect of this new kind of zeolite column.

Purification and characterization of novel antifungal compounds from the sourdough Lactobacillus plantarum strain 21B

Sourdough lactic acid bacteria were selected for antifungal activity by a conidial germination assay. The 10-fold-concentrated culture filtrate of Lactobacillus plantarum 21B grown in wheat flour hydrolysate almost completely inhibited Eurotium repens IBT18000, Eurotium rubrum FTDC3228, Penicillium corylophilum IBT6978, Penicillium roqueforti IBT18687, Penicillium expansum IDM/FS2, Endomyces fibuliger IBT605 and IDM3812, Aspergillus niger FTDC3227 and IDM1, Aspergillus flavus FTDC3226, Monilia sitophila IDM/FS5, and Fusarium graminearum IDM623. The nonconcentrated culture filtrate of L. plantarum 21B grown in whole wheat flour hydrolysate had similar inhibitory activity. The activity was fungicidal. Calcium propionate at 3 mg ml(-1) was not effective under the same assay conditions, while sodium benzoate caused inhibition similar to L. plantarum 21B. After extraction with ethyl acetate, preparative silica gel thin-layer chromatography, and chromatographic and spectroscopic analyses, novel antifungal compounds such as phenyllactic and 4-hydroxy-phenyllactic acids were identified in the culture filtrate of L. plantarum 21B. Phenyllactic acid was contained at the highest concentration in the bacterial culture filtrate and had the highest activity. It inhibited all the fungi tested at a concentration of 50 mg ml(-1) except for P. roqueforti IBT18687 and P. corylophilum IBT6978 (inhibitory concentration, 166 mg ml(-1)). L. plantarum 20B, which showed high antimold activity, was also selected. Preliminary studies showed that phenyllactic and 4-hydroxy-phenyllactic acids were also contained in the bacterial culture filtrate of strain 20B. Growth of A. niger FTDC3227 occurred after 2 days in breads started with Saccharomyces cerevisiae 141 alone or with S. cerevisiae and Lactobacillus brevis 1D, an unselected but acidifying lactic acid bacterium, while the onset of fungal growth was delayed for 7 days in bread started with S. cerevisiae and selected L. plantarum 21B.

[Study on mixed stationary phase composed of 2,3,6-tributyl-beta-cyclodextrin and AgNO3 for capillary gas chromatography]

A new mixed gas chromatographic stationary phase composed of 2,3,6-tributyl-beta-cyclodextrin and AgNO3(in polyethylene glycol 400) was synthesized for the first time. It was coated on fused silica capillary column. Excellent selectivity was obtained for the separation of seven enantiomeric pairs and four groups of positional isomers of aromatic compounds. The recognition and separation mechanisms were discussed by measuring enthalpy, entropy, free energy and the difference in enthalpy and entropy of these compounds. Results were compared with those obtained on 2,3,6-tributyl-beta-cyclodextrin stationary phase. The results showed that the mixed stationary phase had positive synergistic effects.

Effect of Salvia miltiorrhiza on aflatoxin B1-induced oxidative stress in cultured rat hepatocytes

Recent findings have suggested that oxidative damage might contribute to the cytotoxicity and carcinogenicity of aflatoxin B1 (AFB1). Salvia miltiorrhiza (Sm), a herbal plant that has been used extensively in traditional Chinese medicine for treating cardiovascular and liver diseases, is believed to have some antioxidative capabilities. In this study, the protective effect of Sm against AFB1-induced cytotoxicity was investigated in cultured primary rat hepatocytes. AFB1-induced cytotoxicity and lipid peroxidation (LPO) were estimated by determination of lactate dehydrogenase (LDH) leakage and thiobarbituric acid reactive substances (TBARS) formation, respectively. Intracellular reactive oxygen species (ROS) formation was measured using a fluorescent probe 2',7'-dichlorofluorescein diacetate (DCFH-DA). In addition, changes of intracellular glutathione (GSH) content were also studied. Results showed that Sm was able to suppress the LDH leakage induced by AFB1 in a dose-dependent manner. A dose-dependent inhibitory effect of Sm on AFB1-induced LPO was also found in hepatocytes treated with Sm. It was further observed that Sm produced an inhibitory effect on ROS formation caused by AFB1. Concomitantly, the GSH content in Sm-treated groups increased substantially compared to those without Sm treatment. These findings suggest that Sm can inhibit the cytotoxicity of AFB1 through decreasing ROS formation, inhibiting LPO and preventing GSH depletion. The major component of the aqueous extract of Sm was identified by using high performance liquid chromatography (HPLC), proton magnetic resonance (1H-NMR) and mass spectrum (MS). Analytical results suggested that D(+)beta3,4-dihydroxyphenol lactic acid (DA) is the main compound of the aqueous extract of Sm.

Purification and characterization of anti-Listeria compounds produced by Geotrichum candidum

Geotrichum candidum can produce and excrete compounds that inhibit Listeria monocytogenes. These were purified by ultrafiltration, centrifugal partition chromatography, thin-layer chromatography, gel filtration, and high-pressure liquid chromatography, and analyzed by liquid chromatography-mass spectrometry, infrared spectrometry, nuclear magnetic resonance spectrometry, and optical rotation. Two inhibitors were identified: D-3-phenyllactic acid and D-3-indollactic acid.

An aminopeptidase N deficiency in dog small intestine

This study has identified a naturally occurring, specific deficiency of a brush border aminopeptidase N (ApN) in the small intestines of five clinically healthy dogs. ApN activity in mucosal homogenates of dog small intestine was reduced significantly in deficient animals (13.4 (1.1) nmol min-1 mg-1 protein, n = 5, P < 0.002) compared to healthy control dogs (95.1 (6.7), n = 22). Alkaline phosphatase, gamma-glutamyl transferase, zinc-resistant alpha-glucosidase, maltase, sucrase and lactase in the ApN deficient dogs exhibited comparable activities to those in the control dogs. Microvillar membranes were analysed by one- and two-dimensional electrophoresis. ApN was represented by a single 145kDa band in all control dogs, identified by immunoblotting and immunoprecipitation. Protein maps from deficient dogs were normal apart from the virtual absence of an ApN spot and there were no apparent abnormalities in the glycosylation of microvillar proteins. The findings suggest that intestinal ApN deficiency in these dogs is a primary lesion involving diminished expression of an otherwise normal enzyme protein.

Further study on the use of uncharged beta-cyclodextrin polymer in capillary electrophoresis: enantiomeric separation of some alpha-hydroxy acids

Uncharged beta-cyclodextrin polymer was used as chiral selector for the enantiomeric separation of some alpha-hydroxy acids by capillary electrophoresis. Complexation and enantiomeric resolution of mandelic acid, m-hydroxy and p-hydroxymandelic acid, 3,4-dihydroxymandelic acid, as well as 2- and 3-phenyllactic acid were studied, changing the concentration of the beta-cyclodextrin polymer added to the background electrolyte at different pH in the range of 4.5-7. Furthermore, the effects of the concentration of the background electrolyte, column temperature, and applied voltage on chiral resolution were also examined. The best enantiomeric separations were obtained using a background electrolyte at pH 6 containing 100 mg/mL of beta-cyclodextrin polymer.

Novel antioxidants from roasted perilla seed

Novel antioxidants, 5-(3,4-dihydroxyphenylmethyl)oxazolidine-2,4-dione (1) and 3-(3,4-dihydroxyphenyl)lactamide (2), have been isolated from roasted perilla seed. Compound 1 was the first example of non-synthetic oxazolidinedione.

Stealth Me.PEG-PLA nanoparticles avoid uptake by the mononuclear phagocytes system

Nanoparticles were prepared from methoxy poly(ethylene glycol)poly(d,l-lactic acid) block copolymers (Me.PEG-PLA) or blends of Me.PEG-PLA and PLA by the precipitation-solvent diffusion method. These nanoparticles, labeled by introducing [14C]PLA in the formulation, were shown to be more slowly captured by cultured THP-1 monocytes than F68-coated PLA nanoparticles, in a PEG chain-length-dependent manner. In vivo, the half-life in plasma of the Me.PEG-PLA nanoparticles that were intravenously administered to rats is increased by a factor 180 compared with the F68-coated PLA nanoparticles. This mononuclear phagocytes system avoidance was explained according to a conformation model in which the PEG density at the surface of the particles is a key parameter.

Tissue lactate in pediatric head trauma: a clinical study using 1H NMR spectroscopy

In order to define the metabolic abnormalities associated with different types of pediatric head injury, proton magnetic resonance spectroscopy was performed on 21 cerebral regions obtained from 17 patients. On the basis of MRI scans, the regions of interest were classified as normal (6 hemispheres), or showing diffuse axonal injury (3 hemispheres), contusion (4 hemispheres), or cerebral infarction (8 hemispheres). In comparison with normal brain there was no significant elevation in tissue lactate in the diffuse axonal injury patients, but a significant increase in the regions of contusion and infarction. It is concluded that treatment strategies using buffering agents are most likely to benefit these two groups of patients.

Quality improvement of spray-dried, protein-loaded D,L-PLA microspheres by appropriate polymer solvent selection

The aim was to study the effect of the type of polymer solvent on characteristics of microspheres produced by spray drying. The water-soluble model protein, bovine serum albumin (BSA) was microencapsulated into biodegradable poly(D,L-lactic acid) using the following 10 different polymer solvents: acetaldehyde dimethyl acetal, acetone, dichloromethane, dioxane, ethyl acetate, ethyl vinyl ether, nitromethane, tetrahydrofuran, 1,1,1-trichloroethane, and 1,1,2-trichloroethylene. These solvents having similar toxicity levels differ greatly in their physico-chemical characteristics such as boiling point, vapour pressure, miscibility and interfacial tension with an aqueous phase, and solubility parameter. The effect of these solvents on microsphere morphology was studied by SEM-micrographs. Regular particle morphology was obtained when dichloromethane, ethyl acetate, or nitromethane was used as the polymer solvent, whereas the trichlorinated solvents, tetrahydrofuran, and dioxane produced a substantial number of coalesced particles. The results are interpreted in terms of boiling point, vapour pressure, and polymer-solvent affinity. Further, BSA-loading and -integrity in the microspheres, and burst release were analysed. The theoretical loading of 2.9% was attained with dichloromethane, ethyl acetate and nitromethane, in agreement with observations of particle morphology. HPLC- and SDS-PAGE analysis of the microencapsulated BSA did not show any protein degradation or dimerization, whereas solid-phase ELISA clearly revealed that the in vitro protein antigenicity was substantially reduced (50%), particularly by water miscible solvents. Dichloromethane and ethyl acetate did not show any detrimental effect on protein antigenicity. Finally, burst release could be related again to particle morphology, with dichloromethane and nitromethane giving a burst release of only 5%. In conclusion, dichloromethane, ethyl acetate and nitromethane proved to be the most suitable solvents for the polymer-protein system studied.

Biocompatibilities of organic solvents with Lactobacillus delbrueckii

In the search for biocompatible extractants for extractive fermentation of lactic acid, the effect of twelve organic solvents on the activity of L. delbrueckii were studied at different concentration levels. On this basis, the compatibilities of twelve solvents with L. delbrueckii were summarized into four classes: completely compatible, compatible at molecular level, partially compatible and non-compatible. The characteristics were described qualitatively for each class in terms of relative values between the solubility of organic solvent in water (Cs) and the toxicity of organic solvent, which is indicated by a newly defined concentration parameter (Cm). The classification was helpful for the selection of extractant in extractive fermentation.

Quantification of glucose cycling and the extent of equilibration of glucose 6-phosphate with fructose 6-phosphate in islets from ob/ob mice

Pancreatic islets from fed and fasted obese hyperglycaemic (ob/ob) mice were incubated with [1-14C]glucose at 5.5 mM and 16.7 mM, [1-14C]mannose at 16.7 mM, and 3H2O. Yields of 14CO2 and 14C-labelled lactate, and amounts of 14C from [1-14C]mannose incorporated into glucose and of 3H bound to C-2 of glucose, were measured. Glucose utilization was determined from yields of 3H2O from [5-3H]glucose. From the results using 14C, 32-43% of the hexoses phosphorylated to hexose 6-phosphate were estimated to have been dephosphorylated, i.e. cycled. Estimates of hexose cycling from 3H incorporation into glucose were similar. Differences in the ratios of 14C yields in CO2 and lactate indicated incomplete isotopic equilibration between glucose 6-phosphate and fructose 6-phosphate, making the estimates of cycling semi-quantitative. In the fasted state, a larger percentage of the hexose utilized went to lactate than in the fed state. Thus conversion of mannose into glucose in islets indicates the occurrence of glucose cycling in islets. Yields of 14C from [1-14C]mannose, compared with from [1-14C]glucose, provide an approach for quantifying the extent of this cycling. These data provide further evidence for extensive glucose cycling occurring in ob/ob islets in both the fed and the fasted state.