Biomedical subjects

Y Liang

Publications and source records attributed to Y Liang.

At least 73 records · Page 4Linked to original sources

PubMed2001

Formation of Monolayer Lipid Membranes in Water and Ethanol from Bolaamphiphiles.

Three single-chain bolaamphiphiles containing two salicylidene units per molecule as the rigid segment were synthesized. Their aggregation behavior in water and ethanol has been studied. They can form monolayer membranes not only in water solution but also in pure ethanol. The presence of a relatively short methylene chain as a spacer at the center of the molecule has a dramatic influence on the morphology of the aggregates formed. Copyright 2001 Academic Press.

Journal Article↗

PubMed2001

Regulation of an endogenous locus using a panel of designed zinc finger proteins targeted to accessible chromatin regions. Activation of vascular endothelial growth factor A.

We have mapped conserved regions of enhanced DNase I accessibility within the endogenous chromosomal locus of vascular endothelial growth factor A (VEGF-A). Synthetic zinc finger protein (ZFP) transcription factors were designed to target DNA sequences contained within the DNase I-hypersensitive regions. These ZFPs, when fused to either VP16 or p65 transcriptional activation domains, were able to activate expression of the VEGF-A gene as assayed by mRNA accumulation and VEGF-A protein secretion through a range exceeding that induced by hypoxic stress. Importantly, multiple splice variants of VEGF-A mRNA with defined physiological functions were induced by a single engineered ZFP transcription factor. We present evidence for an enhanced activation of VEGF-A gene transcription by ZFP transcription factors fused to VP16 and p65 targeted to two distinct chromosomal sites >500 base pairs upstream or downstream of the transcription start site. Our strategy provides a novel approach for dissecting the requirements for gene regulation at a distance without altering the DNA sequence of the endogenous target locus.

Cell Line, Transformed↗

PubMed2001

Spectroscopic studies of interaction of chlorobenzylidine with DNA.

Electronic absorbance and fluorescence titrations are used to probe the interaction of chlorobenzylidine with DNA. The binding of chlorobenzylidine to DNA results in hypochromism, a small shift to a longer wavelength in the absorption spectra, and emission quenching in the fluorescence spectra. These spectral characteristics suggest that chlorobenzylidine binds to DNA by an intercalative mode. This conclusion is reinforced by fluorescence polarization measurements. Scatchard plots constructed from fluorescence titration data give a binding constant of 1.3 x 10(5) M(-1) and a binding site size of 10 base pairs. This indicates that chlorobenzylidine has a high affinity with DNA. The intercalative interaction is exothermic with a Van't Hoff enthalpy of -143 kJ/mol. This result is obtained from the temperature dependence of the binding constant. The interaction of chlorobenzylidine with DNA is affected by the pH value of the solution. The binding constant has its maximum at pH 3.0. Upon binding to DNA, the fluorescence from chlorobenzylidine is quenched efficiently by the DNA bases and the fluorescence intensity tends to be constant at high concentrations of DNA when the binding is saturated. The Stern-Volmer quenching constant obtained from the linear quenching plot is 1.6 x 10(4) M(-1) at 25 degrees C. The measurements of the fluorescence lifetime and the dependence of the quenching constant on the temperature indicate that the fluorescence quenching process is static. The fluorescence lifetime of chlorobenzylidine is 1.9 +/- 0.4 ns.

Animals↗

PubMed2001

Study of gas-phase molecular recognition using Fourier transform ion cyclotron resonance mass spectrometry (FTICR/MS).

The application of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry to the quantitative study of molecular recognition in the gas phase is reviewed. Because most quantitative measurements are dependent on accurate determination of the pressure of a neutral reagent, methods for accurate pressure measurement in FTICR, including gauge calibration using a reaction with known rate constants (the traditional method), exothermic proton transfer rate measurement (often the best method when accurate neutral pressures in the trapping cell are desired), and linewidth measurement (a little-used, but generally applicable method) are discussed. The use of rate constant measurements in molecular recognition is illustrated with examples employing natural abundance isotopic labeling to study self-exchange and 2 : 1 ligand:metal complex formation kinetics in crown ether-alkali cation systems. Self-exchange rates do not correlate with alkali cation/crown cavity size relationships, whereas 2 : 1 complex formation kinetics correlate strongly with size relationships. The use of exchange equilibrium constant measurements to characterize molecular recognition is illustrated by alkali cation exchanges between 18-crown-6 and the isomers of dicyclohexano-18-crown-6. These experiments show that the alkyl-substituted ligand binds alkali cations better than unsubstituted 18-crown-6 in the gas phase, in accordance with expectations based on the higher polarizability of the alkyl-substituted ligand. Further, the metal binding thermochemistry differs for the two dicyclohexano-18-crown-6 isomers, with the bowl-shaped cis-syn-cis isomer binding all the alkali cations more strongly than the cis-anti-cis isomer. The measurement of entropies and enthalpies associated with one of the most subtle forms of molecular recognition, enantiomeric discrimination, is illustrated by studies of the discrimination between enantiomers of chiral amines by dimethyldiketopyridino-18-crown-6. This chiral ligand binds chiral primary ammonium cations that have the opposite absolute configuration at their stereocenter more strongly than the enantiomer with the same absolute configuration. Gas-phase studies show that this enantiomeric discrimination is enthalpic in origin, likely related to more favorable pi-pi stacking for the preferred enantiomer. Entropy disfavors binding of the preferred enantiomer.

Journal Article↗

PubMed2001

Three-dimensional morphological analysis of antigen-antibody reaction in hepatic sinusoids preserved in hypothermic UW solution.

ICAM-1 antigen-antibody reaction was visualized by three-dimensional immunoscanning electron microscopy of hepatic sinusoids in rat liver treated with hypothermic University of Wisconsin (UW) organ preservation solution. The results were compared with similar antigen-antibody reactions carried out with immunoliposomes injected in vivo. Morphologically, the hepatic sinusoids were preserved well during the hypothermic procedure. Endothelial cells had a large number of fenestrations, which partly aggregated and formed sieve plates. ICAM-1 expression was induced by injection of LPS and detected by monoclonal antibody in the UW solution followed by gold-labeled secondary antibody. ICAM-1 was restricted mostly to the unique areas of sieve plates with immature, small fenestrations. A similar distribution of ICAM-1 was present when detected by in vivo injection of immunoliposomes containing the monoclonal ICAM-1 antibody. The results showed that antigen-antibody reactions can take place in livers preserved in hypothermic UW solution. Further, the reaction is similar to that which could occur in vivo during transplantation. This suggests that it may be possible to block potentially harmful antigen-antibody reactions by addition of appropriate antibodies to hypothermic UW solution prior to transplantation.

Adenosine↗

PubMed2001

Superantigen presentation by human retinal pigment epithelial cells to T cells is dependent on CD2-CD58 and CD18-CD54 molecule interactions.

Human retinal pigment epithelial (RPE) cells are capable of presenting bacterial superantigens (SAg) to T cells in vitro by ligation of MHC class II molecules on RPE cells with the T cell receptor. The purpose of this study was to evaluate the involvement of adhesion molecules in presentation of SAg. Cultured human fetal and adult RPE cells were treated with interferon-gamma (IFN-gamma, 500 U ml(-1) for 72 hr) and afterwards pulsed with the SAg staphylococcal enterotoxin A (SEA, 500 ng ml(-1) for 2 hr) followed by coculture with freshly obtained T cells isolated from peripheral blood. Proliferation was measured by (3)H-thymidine incorporation assay. In selected experiments, either RPE or T cells were pre-treated with blocking antibodies specific for cell surface molecules. For comparison, dendritic cells were used as superantigen presenting cells for T cells. This study showed that presentation of SEA by RPE cells to resting T cells was dependent on the presence of the molecules CD2, CD58 and CD18, CD54. The cycling status of T cells was decisive, thus resting T cells but not activated T cells were capable to proliferate in response to SEA presentation. Proliferation of T cells induced by adult RPE cells was comparable to the proliferation induced by dendritic cells at concentrations of SAg above 100 ng ml(-1), but at concentrations of SAg below 10 ng ml(-1) the response was significantly lower for SAg presented by RPE cells compared to dendritic cells. The results demonstrate that CD2-CD58 and CD18-CD54 interactions are critical for SAg presentation by RPE cells to T cells. The findings thus suggest that also presentation of peptides to resting T cells by RPE cells may be dependent upon these interactions.

Antibodies, Monoclonal↗

PubMed2001

5-aminoimidazole-4-carboxy-amide-1-beta-D-ribofuranoside treatment ameliorates hyperglycaemia and hyperinsulinaemia but not dyslipidaemia in KKAy-CETP mice.

AIM/HYPOTHESIS: 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside increases 5'-AMP-activated kinase activity in insulin-sensitive tissues known to control glucose homeostasis. We hypothesised that 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside treatment could have a beneficial effect on glucose homeostasis in KKAy-CETP mice, a model of Type II (non-insulin-dependent) diabetes mellitus. Our aim was to examine potential effects of acute and chronic (7-day) 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside treatment on glucose homeostasis in KKAy-CETP diabetic mice. METHODS: Female KKAy-CETP mice were treated with 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside by a single daily injection for 7 days (100, 300, or 500 mg. kg-1. day-1). RESULTS: After 7 days of treatment with 500 mg. kg-1. day-1 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside, blood glucose and plasma insulin concentrations were reduced (p < 0.01). Body weight and food intake were also reduced after treatment (p < 0.01 and p < 0.05, respectively). Glucose and insulin tolerance were improved (p < 0.05), whereas endogenous glucose production was suppressed (p < 0.05). The beneficial effect of 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside on hyperglycaemia and hyperinsulinaemia was due to an inhibition of endogenous glucose production, since in vivo and in vitro basal and insulin-stimulated glucose uptake in skeletal muscle was not affected by 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside. Other features of the treatment included increased plasma of free fatty acid concentration (1.9-fold, p < 0.01) and triglycerides (1.3-fold, p < 0.05). CONCLUSION/INTERPRETATION: 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside treatment attenuated hyperglycaemia and hyperinsulinaemia but not dyslipidaemia in KKAy-CETP mice, a model of Type II diabetes. The blood glucose lowering effects of 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside occurs mainly as a consequence of reduced endogenous glucose production because insulin-stimulated skeletal muscle glucose uptake has not been altered.

Aminoimidazole Carboxamide↗

PubMed2001

Resolution of two-way data: theoretical background and practical problem-solving. Part 1: theoretical background and methodology.

This paper reviews recent progress in the resolution of two-way data obtained from hyphenated instruments. Special emphasis is placed on the solution of practical problems. Methods for estimating the number of chemical components both statistically and visually (the first step in solving the resolution problem) and methods for resolving the pure profiles (the second step in solving the resolution problem) are discussed in detail. To deal with real-world problems, pitfalls in the chemometric analysis of the two-way data from the instrumental measurements are also pointed out. Applications of methods for solving some difficult practical problems in environmental chemistry, pharmaceutical chemistry, and physical chemistry will be discussed in the second part of this paper.

Journal Article↗

PubMed2001

Structural organization of the human MS4A gene cluster on Chromosome 11q12.

CD20, the high-affinity IgE receptor beta chain (FcepsilonRIbeta), and HTm4 are structurally related cell surface proteins expressed by hematopoietic cells. Recently, 16 novel human and mouse genes were identified that encode new members of this nascent protein family that we have named the membrane-spanning 4A gene family, with at least 12 subgroups (MS4A1-MS4A12). In the current study, we identified three additional human MS4A genes: MS4A4E, MS4A6E, and MS4A10. All family members have at least four potential transmembrane domains and N- and C-terminal cytoplasmic domains encoded by distinct exons, except MS4A6E which contains two transmembrane domains. Otherwise, the 12 currently identified MS4A genes share common structural features and similar intron/exon splice boundaries, and are clustered along an approximately 600-kb region of Chromosome 11q12. In contrast to other MS4A genes, MS4A4E, MS4A6E, and MS4A10 transcripts were rare and not detected among hematopoietic cells and most nonlymphoid tissues. Sequence polymorphisms were identified in the MS4A6E gene and common splice variants were observed for the MS4A4A, MS4A5, MS4A6A, and MS4A7 genes. Thus, the MS4A family currently includes 24 distinct human and mouse genes. Like CD20 and FcepsilonRIbeta, the 10 other human MS4A family members are likely to be components of oligomeric cell surface complexes involved in signal transduction in diverse cell lineages.

Amino Acid Sequence↗

PubMed2001

Mutations in the open reading frame of the beta-site APP cleaving enzyme (BACE) locus are not a common cause of Alzheimer's disease.

Amyloid beta-peptide (Abeta) plays a central role in the pathogenesis of Alzheimer's disease (AD). The gene encoding the beta-site APP cleaving enzyme (BACE), one of two enzymes that sequentially cleave the beta-amyloid precursor protein to generate Abeta, has recently been cloned. We tested the hypothesis that BACE might be genetically associated with AD by linkage analysis (56 pedigrees), by direct nucleotide sequencing of the entire open reading frame (20 subjects with familial AD, and 10 subjects with sporadic AD) and by allelic association analysis (155 AD cases and 173 non-demented controls). Our results revealed no evidence for either genetic linkage or allelic association between BACE and AD, and no coding sequence mutations were detected in the open reading frame of the BACE gene. These data suggest that while BACE protein plays an important role in the pathogenesis of AD, and may be a robust therapeutic target, it is unlikely to be a major AD susceptibility locus.

Aged↗

PubMed2001

The pharmacology of bimatoprost (Lumigan).

Bimatoprost (Lumigan) is a pharmacologically unique and highly efficacious ocular hypotensive agent. It appears to mimic the activity of a newly discovered family of fatty acid amides, termed prostamides. One biosynthetic route to the prostamides involves anandamide as the precursor. Bimatoprost pharmacology has been extensively characterized by binding and functional studies at more than 100 drug targets, which comprise a diverse variety of receptors, ion channels, and transporters. Bimatoprost exhibited no meaningful activity at receptors known to include antiglaucoma drug targets as follows: adenosine (A(1-3)), adrenergic (alpha(1), alpha(2), beta(1), beta(2)), cannabinoid (CB(1), CB(2)), dopamine (D(1-5)), muscarinic (M(1-5)), prostanoid (DP, EP(1-4), FP, IP, TP), and serotonin (5HT(1-7)). Bimatoprost does, however, exhibit potent inherent pharmacological activity in the feline iris sphincter preparation, which is prostamide-sensitive. Bimatoprost also resembles the prostamides in that it is a potent and highly efficacious ocular hypotensive agent. A single dose of bimatoprost markedly reduces intraocular pressure in dogs and laser-induced ocular hypertensive monkeys. Decreases in intraocular pressure are well maintained for at least 24 hr post-dose. Human studies have demonstrated that systemic exposure to bimatoprost is low and that accumulation does not occur. The sclera is the preferred route of accession to the eye. The high scleral permeability coefficient Papp is a likely contributing factor to the rapid onset and long-acting ocular hypotensive profile of bimatoprost.

Amides↗

PubMed2001

Membrane fluidity effects of estratrienes.

Estrogens have demonstrable neuroprotective effects. This fact has lead to the proposed use of estrogens for the prevention and/or treatment of Alzheimer's disease. The exact protective mechanism estrogens provide is not fully understood. In this report, a potential non-genomic mechanism for estratrienes involving alterations in membrane fluidity was studied. Steroids, such as estrogen, are known to be membrane-active and can alter the lipid packing. In this study we used fluorescent methodologies to address the effect of naturally occurring steroids (17alpha and 17beta-estradiol, testosterone, and progesterone) and new estratriene analogs on membrane fluidity using liposomes and HT-22 hippocampal cells. The study's results indicate steroids, based on the estratriene nucleus, can modulate lipid packing as evidenced by (1) decreased membrane fusion events and (2) decreased membrane fluidity. The effects on the membrane were both time and concentration dependent. It was also demonstrated through rational design estratriene analogs can be synthesized with enhanced membrane effects. Finally, in a glutamate-induced toxicity HT-22 model, we also demonstrated cellular protection with the estratriene-based molecules and analogs. The data suggest the plethora of cellular actions of estrogens may relate to or be influenced by membrane effects of the steroid.

Alzheimer Disease↗

PubMed2001

Expression of adhesion molecules and fibronectin of activated peritoneal surface with lipopolysaccharide (LPS) analyzed with immuno SEM.

To disclose cell-to-cell interaction associated with the defensive mechanism of the peritoneum, the peritoneum was stimulated with lipopolysaccharide (LPS) and analyzed three-dimensionally, ultrastructurally, and immunohistochemically with immunoSEM (scanning electron microscopy). The activated hepatic peritoneal surface demonstrated numerous microvilli with the adhesion molecules ICAM-1 and VCAM-1. They were restricted to villi and peaked at 1.5 microg/g body weight of LPS. Delicate strands appeared moderately and were interwoven among microvilli with increasing LPS. These strands did not express ICAM-1 or VCAM-1, but fibronectin. Leukocytes began to adhere to the peritoneal surface above die value of LPS (2.5 microg). These results suggest that the peritoneal surface gives a defensive sheet for cell-to-cell interaction through adhesion molecules and fibronectin.

Animals↗

PubMed2001

Selection with melphalan or paclitaxel (Taxol) yields variants with different patterns of multidrug resistance, integrin expression and in vitro invasiveness.

A melphalan-resistant variant (Roswell Park Memorial Institute (RPMI)-2650Ml) and a paclitaxel-resistant variant (RPMI-2650Tx) of the drug-sensitive human nasal carcinoma cell line, RPMI-2650, were established. The multidrug resistance (MDR) phenotype in the RPMI-2650Tx appeared to be P-glycoprotein (PgP)-mediated. Overexpression of multidrug resistant protein (MRP) family members was observed in the RPMI-2650Ml cells, which were also much more invasive in vitro than the parental cell line or the paclitaxel-resistant variant. Increased expression of alpha(2), alpha(5), alpha(6), beta(1) and beta(4) integrin subunits, decreased expression of alpha(4) integrin subunit, stronger adhesion to collagen type IV, laminin, fibronectin and matrigel, increased expression of MMP-2 and MMP-9 and significant motility compared with the parental cells were observed, along with a high invasiveness in the RPMI-2650Ml cells. Decreased expression of the alpha(2) integrin subunit, decreased attachment to collagen type IV, absence of cytokeratin 18 expression, no detectable expression of gelatin-degrading proteases and poor motility may be associated with the non-invasiveness of the RPMI-2650Tx variant. These results suggest that melphalan exposure can result in not only a MDR phenotype, but could also make cancer cells more invasive, whereas paclitaxel exposure resulted in MDR without increasing the in vitro invasiveness in the RPMI-2650 cells.

Antigens, CD↗

PubMed2001

Spectroscopic studies on molecular recognition capabilities of a nucleolipid bearing thymine headgroup to adenosine.

The Langmuir-Blodgett (LB) films of octadecanoyl ester of 1-(2-carboxyethyl) thymine deposited from pure water and aqueous adenosine subphases were investigated by ultraviolet-visible (UV-vis), Fourier transform infrared-attenuated total reflection (FTIR-ATR), and Fourier transform surface-enhanced Raman scattering (FT-SERS) spectroscopy. The obtained spectral results indicate that the adenosine molecules in the subphase can be transferred onto solid substrates by LB techniques as a result of the formation of base pairs at the air/water interface. UV-vis spectra alternations indicated that, with increasing adenosine concentration in subphase, more adenosine molecules were recognized by nucleolipid monolayer and were transferred onto the quartz substrates. The closed-packing of the constituent molecules facilitates the photodimerization of the thymine moieties in the headgroup under ultraviolet irradiation. FTIR-ATR results suggest that the hydrocarbon chains of nucleolipid in the LB films deposited from pure water and aqueous adenosine take on a close-packed all trans conformation. By analyzing the FT-SERS spectra results, it can be deduced that the orientation of nucleobase in the headgroup is different before and after the recognition effect occurred. For LB film deposited from pure water, the nucleobases are lying flat on the silver substrates; whereas for LB film deposited from aqueous adenosine, the base pairs take an end-on adsorption on silver substrate.

Adenosine↗

PubMed2001

Cutaneous mast cells are altered in normal healthy volunteers sitting in front of ordinary TVs/PCs--results from open-field provocation experiments.

BACKGROUND: Considerable controversy has surrounded the question of possible biological responses to electromagnetic fields (EMFs) generated from visual display terminals (VDTs), such as personal computers (PCs) and ordinary television sets (TVs). The cellular and molecular mechanisms for such potential harmful health hazards have not yet been understood, although clues from the literature include mast cells and histamine. The aim of this study was therefore to investigate possible biological mast cell responses to TV/PC screens. METHODS: Using the indirect immunofluorescence technique, we studied the presence of histamine-containing mast cells in the dermis of healthy volunteers. Cutaneous biopsies taken before and after exposure to ordinary TV/PC screens for 2 or 4 h were investigated in 13 healthy subjects. RESULTS: Our present in vivo study indicates that normal cutaneous mast cells could be altered by exposure from ordinary TV/PC screens. To our great surprise, we found the number of mast cells in the papillary and reticular dermis to increase, to varying degrees, in 5 out the 13 subjects after such an exposure. A migration of mast cells towards the uppermost dermis appeared as the most important event. Thus, the normally upper "empty zone" of the dermis disappeared, and instead, a higher density of mast cells were found in this zone. These cells also seemed to have a tendency to increase in number towards the epidermal-dermal junctional zone and some of them lost their granular content and the cytoplasm shrunk (=degranulation). These findings could only be seen in the exposed skin. Two of the 13 cases instead showed a decrease in mast cell number, but the shift in mast cells towards the upper dermis was still visible. Twenty-four h after the provocation, the cellular number and location were normalized in all subjects. CONCLUSIONS: By definition, normal healthy volunteers are assumed not to react to a TV/PC screen provocation. To our great surprise, this proved not to be true. The present results might lay a foundation to understand the underlying cause of so-called "screen dermatitis" with special reference to mast cells. However, blind or double-blind experiments using patients ought to be further investigated in order to find out the exact cause for the observed changes. Such causes include the effects of surrounding airborne chemicals, stress factors, etc.

Adult↗

PubMed2001

Endogenous nicotinic cholinergic activity regulates dopamine release in the striatum.

Dopamine is vital for coordinated motion and for association learning linked to behavioral reinforcement. Here we show that the precise overlap of striatal dopaminergic and cholinergic fibers underlies potent control of dopamine release by ongoing nicotinic receptor activity. In mouse striatal slices, nicotinic antagonists or depletion of endogenous acetylcholine decreased evoked dopamine release by 90%. Nicotine at the concentration experienced by smokers also regulated dopamine release. In mutant mice lacking the beta2 nicotinic subunit, evoked dopamine release was dramatically suppressed, and those mice did not show cholinergic regulation of dopamine release. The results offer new perspectives when considering nicotine addiction and the high prevalence of smoking in schizophrenics.

Acetylcholine↗

PubMed2001

Increased responsiveness to the hyperglycemic, hyperglucagonemic and hyperinsulinemic effects of circulating norepinephrine in ob/ob mice.

OBJECTIVE: Several studies have implicated increased sympathetic tone as a contributing factor to the hyperglycemia and hyperglucagonemia of ob/ob mice. However, the responsiveness of plasma glucose, insulin and glucagon to circulating norepinephrine (NE) in ob/ob vs normal lean mice has never been described. Therefore, the present study investigated the effect of a 15 min intravenous NE infusion (1 pmol/min/g) on plasma glucose, insulin and glucagon in anesthetized lean, ob/ob, ob/ob-concurrent yohimbine (alpha(2) antagonist) treated, and ob/ob-chronically sympatholytic dopamine agonist treated (for 14 days prior to infusion) mice. In an effort to gain insight into a possible relation between norepinephrine, hyperglucagonemia and hyperinsulinemia in ob/ob mice, this study also examined the isolated islet responses to NE and glucagon in lean, ob/ob and ob/ob-sympatholytic dopamine agonist treated mice. RESULTS: Basal humoral values of glucose, insulin and glucagon were all elevated in ob/ob vs lean mice (by 63, 1900 and 63%, respectively, P<0.01). However, NE infusion further increased levels of glucose, insulin and glucagon in ob/ob (by 80, 90 and 60%, respectively, P<0.05) but not in lean mice (between group difference for all parameters P<0.05). Acute concurrent yohimbine treatment as well as chronic prior sympatholytic dopamine agonist treatment (bromocriptine plus SKF38393) simultaneously strongly aborgated or abolished all these humoral hypersensitivity responses to intravenous NE in ob/ob mice (P<0.05). Clamping the plasma glucose level in untreated ob/ob mice at a high level (30 mM) established by NE infusion did not significantly alter the plasma insulin level, suggesting that some other influence of NE was responsible for this insulin effect. Direct NE administration at 1 microM to islets from lean and ob/ob mice inhibited 15 mM glucose-stimulated insulin secretion in both groups, but at 0.1 microM it was inhibitory only in islets from ob/ob mice. However, glucagon (10 nM) increased 15 mM glucose-stimulated insulin secretion in ob/ob (by 170%, P<0.05) but not lean mice (between group difference P<0.05). CONCLUSION: These findings suggest that hypersensitivity to circulating NE may potentiate hyperglycemia and hyperglucagonemia in ob/ob mice, and the subsequent hyperglucagonemia coupled with increased islet beta-cell insulin secretory responsiveness to glucagon in ob/ob mice may support hyperinsulinemia, thus explaining the increased plasma insulin level response to intravenous NE in these animals. These findings further support a role for increased peripheral noradrenergic activities in the development and maintenance of the hyperglycemic, hyperglucagonemic and hyperinsulinemic state, characteristic of type 2 diabetes.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗