Clinical pharmacology of β3-adrenoceptors

1An atypical non β₁/β₂-adrenoceptor (AR) subtype (β₃-AR) has been identified which is selectively stimulated by a group of ligands which mediate lipolytic and thermic responses in brown and white adipose tissue. 2Molecular studies have shown that β₃-AR in man are mainly expressed in visceral adipocytes, and to a lesser extent in gall-bladder and colon. In vitro studies with β₃-AR agonists have shown activity at other sites including skeletal muscle and myocardium. 3Regulation of β₃-AR may differ from β₁/β₂-AR subtypes in that continuous agonist exposure does not result in receptor down-regulation. 4A polymorphism of the human β₃-AR gene (Trp64Arg) has been identified which is associated with obesity, insulin resistance and an earlier onset of non-insulin-dependent diabetes mellitus (NIDDM). Studies are required to establish whether expression of the mutant gene results in altered metabolic responses to β₃-AR stimulation in man. 5There is accumulating evidence to support a therapeutic role of β₃-AR agonists in NIDDM because of anti-obesity and anti-diabetic activity, as a consequence of thermogenic effects as well as increased insulin sensitivity and glucose tolerance. 6Selectivity studies with BRL35135 and isoprenaline in humans have demonstrated a β₃-AR mediated component to thermogenesis which is dissociated from β₁/β₂-mediated effects on carbohydrate and fat metabolism. Similar studies have suggested a functional β₃-AR mediating cardiac but not airway responses in humans. An evaluation of β₃-AR agonists in irritable bowel syndrome may be warranted in view of colonic antimotility properties in vitro.     

β3-Adrenoceptor activation attenuates atherosclerotic plaque formation in ApoE?/? mice through lowering blood lipids and glucose

Aim:

To examine the effects of β₃-adrenoceptor (β₃-AR) activation on atherosclerotic plaque development in ApoE^−/− mice.

Methods:

Thirty six week-old male ApoE^−/− mice on a high-fat diet were treated with atorvastatin (10 mg·kg^-1·d^-1, po), BRL37344 (β₃-AR agonist, 1.65 or 3.30 μg/kg, ip, twice a week) or SR52390A (β₃-AR antagonist, 50 μg/kg, ip, twice a week) for 12 weeks. Wild-type C57BL/6J mice receiving a normal diet were taken as healthy controls. At the end of the treatments, serum levels of triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), non-high density lipoprotein cholesterol (nHDL-C), glucose and insulin were measured. The thoracic aortas were dissected out, the area of atherosclerotic plaques and extent of fibrosis in the plaques were examined using HE and Masson''s trichome staining, respectively.

Results:

Compared to wild-type mice, ApoE^−/− mice fed on a high-fat diet exhibited prominent hyperlipidemia and insulin resistance, associated with large area of atherosclerotic plaques and great extent of fibrosis in aortas. Atorvastatin significantly decreased the serum levels of TC and nHDL-C, and reduced the plaque area and collagen content in aortas. BRL37344 significantly decreased the serum levels of TG, TC, nHDL-C, glucose and insulin, and increased HDL-C and the insulin sensitivity, and dose-dependently reduced the plaque area and collagen content in aortas. SR52390A treatment did not affect any parameters studied.

Conclusion:

The β₃-AR agonist impedes the progression of atherosclerosis in ApoE^−/− mice, through improvement of the lipid and glucose profiles.     

Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists, 1994: SIGNALLING PATHWAYS IN CARDIAC FAILURE

1. Cardiac failure in humans and in animal models is associated with a marked desensitization of the catecholamine signalling pathway. 2. β₁- and β₂- and possibly β₃-adrenoceptors (β-AR) are found in the hearts of humans and common laboratory animals such as rats and guinea-pigs. In rats and guinea-pigs chronic stimulation of cardiac β-AR leads to a rapid loss of β₂-AR whereas heart failure in humans is associated with a loss of β₁-AR or β₁-AR and β₂AR. 3. Desensitization is also associated with phosphorylation of β-AR by β-AR kinase β-ARK) and uncoupling of receptors from the signalling pathway. β-ARK but not β-arrestin activity and mRNA are markedly increased in heart failure. 4. Chronic β-AR stimulation and heart failure are associated with increases in Giα but little if any change in Gsα. 5. The roles of βm? subunits of G-proteins, adenylate cyclase subtypes and cAMP dependent protein kinase A in heart failure are unclear at present.     

METABOLIC EFFECTS OF THIOCTIC ACID IN RODENT MODELS OF INSULIN RESISTANCE AND DIABETES

1. The antioxidant thioctic acid (TA) has been used in the treatment of diabetic neuropathy and recent studies have suggested that TA also has pancreatic and peripheral effects that improve glucose transport and metabolism. In the present study, the metabolic effects of TA were evaluated in rodent models of insulin resistance (fructose-fed Sprague-Dawley rat) and insulin deficiency (streptozotocin (STZ)-induced diabetic rat). Oral and intravenous glucose tolerance tests (OGTT and IVGTT, respectively) were performed in conscious rats after treatment with 50 mg/kg per day TA or vehicle for 5 days. 2. Fructose feeding for 7 days induced insulin resistance and impaired glucose tolerance and hypertriglycerideaemia. Treatment of fructose-fed rats with TA had no significant effect on fasting or stimulated glucose levels or on fasting triglyceride concentrations (e.g. the area under the curve for glucose (AUC_glu) following OGTT was 1233 ± 67 and 1284 ± 59 in fructose-fed rats treated with either TA (n= 12) or vehicle (n= 12), respectively). Similarly, TA had no significant effect on IVGTT profiles in fructose-induced insulin resistance. 3. Low-dose STZ (80 mg/kg, i.p, over 2 days) induced hyper-glycaemia, but TA had no significant glucose-lowering effects in STZ-diabetic rats (AUC_glu (OGTT) following oral administration was 5507 ± 27 and 5450 ± 27 in TA (n= 12) and vehicle-treated (n= 12) rats, respectively). Nor did pretreatment with TA affect the diabetogenic response to STZ. 4. In contrast with previous in vitro studies reporting favourable metabolic effects of TA, the present study shows that after short-term oral therapy there are no significant improvements in glucose tolerance in rodent models of insulin resistance and insulin deficiency. Thioctic acid is unlikely to be of therapeutic benefit as an anti-diabetic drug in clinical practice.     

Trichosanthes cucumerina Linn. improves glucose tolerance and tissue glycogen in non insulin dependent diabetes mellitus induced rats

Objective:

To study the effect of Trichosanthes cucumerina Linn. on non insulin dependent diabetes mellitus induced rats.

Materials and Methods:

Non Insulin Dependent Diabetes Mellitus (NIDDM) was induced by administering streptozotocin (90 mg/kg, i.p.) in neonatal rat model. NIDDM animals were treated with aqueous extract of Trichosanthes cucumerina (100 mg/kg/day) orally for six weeks. Parameters such as fasting blood glucose, Oral Glucose Tolerance Test (OGTT) and tissue glycogen content were evaluated.

Results:

Aqueous extract of Trichosanthes cucumerina significantly (P<0.01) decreased the elevated blood glucose of NIDDM induced rats. OGTT of NIDDM animals showed glucose intolerance. Blood glucose of diabetic animals reached peak at 45 min and remains high even after 2h. In case of Trichosanthes cucumerina treated group, the blood glucose reached peak level at 30 min, followed by decrease in glucose level up to 2h. The drug has significantly (P<0.01) reduced the postprandial blood glucose of diabetic animals. Glycogen content of insulin dependent tissues such as liver and skeletal muscle was found to be improved by 62% and 58.8% respectively with Trichosanthes cucumerina as compared to NIDDM control.

Conclusion:

Studies revealed that, Trichosanthes cucumerina possess antidiabetic activity. The drug improved the oral glucose tolerance of NIDDM subjects. Increase in tissue glycogen content indicates the effect of the drug on the uptake of glucose by the peripheral tissues to reduce insulin resistance of NIDDM.     

Functional characterization of three adenosine receptor types

1 The purpose of the present study was to classify adenosine receptors into A₁ and A₂ subtypes in a wide range of isolated tissues and cell types (rat adipocytes and atria, guinea-pig ileum and atria (A₁); guinea-pig aorta, dog coronary artery and human platelets and neutrophils (A₂)) using the R- and S-diastereoisomers of N-phenylisopropyladenosine (PIA), N-cyclopentyladenosine (CPA), the novel compound, N-[(1S,trans)-2-hydroxycyclopentyl]adenosine (GR79236), N-[(2-methylphenyl)methyl]adenosine (metrifudil), 2-(phenylamino)adenosine (CV1808), and 2-[[2-[4-(2-carboxyethyl)phenyl]ethyl]amino]-N-ethylcarboxamidoadenosine (CGS21680); N-ethylcarboxamidoadenosine (NECA) was used as a standard.2 Results obtained in all tissue preparations previously reported to contain A₁-receptors could be described by a single rank order of agonist potency: CPA ≥ GR79236, R-PIA ≥ NECA >> S-PIA ≥ metrifudil ≥ CV1808, CGS21680.3 In contrast, two distinct rank orders of agonist potency were observed in preparations previously reported to contain A₂-receptors. In dog coronary artery, human neutrophils and platelets the rank order of potency was: CV1808, CGS21680 ≥ NECA > R-PIA ≥ metrifudil ≥ CPA > GR79236, S-PIA. However, in guinea-pig aorta the rank order was: NECA > metrifudil > R-PIA, CPA > CV1808, GR79236 ≥ S-PIA, CGS21680.4 The results of this study are consistent with the existence of three types of adenosine receptor: A₁-and two subtypes of A₂-receptor. The receptor present in dog coronary artery, human platelets and neutrophils, probably corresponds to the A_2a subtype, whilst that present in the guinea-pig aorta may be of the A_2b subtype.     

Increased β2-adrenergic vasorelaxation at the early phase of endotoxemic shock in rats

Background and purposeThe early management of the cardiovascular dysfunction of septic shock is critical as it is associated with a poor outcome. Although the use of catecholamines is a common therapy in this syndrome, no data are available on the involvement of β-adrenoceptor (β-AR) subtypes and only few studies report an alteration of β-adrenergic-induced vasodilation in septic shock. The purpose of the study was to evaluate vascular β₁, β₂ and β₃-AR expression and function in an endotoxemic rat model.Experimental approachEndotoxemia was induced in rats by intravenous injection of lipopolysaccharide (LPS). β₁, β₂ and β₃-AR mRNA expression was evaluated by RT-PCR in aorta and vascular β₁, β₂ and β₃-AR responses were determined on conducting (aorta) and/or resistance (mesenteric and renal) arteries by constructing relaxation curves in response to different β-AR agonists.ResultsThe maximal effect of isoproterenol decreased by 31 to 61% in the three vascular beds of LPS-treated rats compared to controls. In aortas from LPS-treated rats, β₁ and β₃-AR mRNA expression was decreased and associated to a reduced β₁ and β₃-induced vasodilation. Conversely, albeit β₂-AR mRNA was unchanged, the maximal β₂-AR-induced vasodilation increased by 49% in aortas from LPS-treated rats compared to controls. This increase was not affected by endothelium removal but was abolished in the presence of a β₂-AR antagonist or an adenylate cyclase inhibitor.ConclusionsIn endotoxemia, β₂-AR vasodilation was increased by a potential recruitment of β₂-AR located on smooth muscle cells. This study suggests that vascular β₂-AR should be a putative new therapeutic target in septic shock.     

THE EFFECTS OF SYMPATHOMIMETICS ON THE CARDIOVASCULAR SYSTEM OF SHEEP

1. Sheep hearts have been used to study the effects of P-adrenoceptor (P-AR) agonists in order to better understand the effects of common asthma treatment drugs on heart rate, cardiac power output and cardiac pathology. Hearts have been examined both in vivo and in vim. 2. In whole anaesthetized sheep, isoprenaline, fenoterol and salbutamol induced dose-dependent increases in heart rate. Hypokalaemia in response to salbutamol was accentuated in hypoxia. Many of these hearts showed significant myocardial lesions. Hypoxia alone caused no significant cardiac response. 3. As expected, the β₁-AR agonist dobutamine caused dose-dependent increases in heart performance (heart rate and cardiac power output). Both responses were blocked by metoprolol and propranolol. The β₂-AR agonist salbutamol caused dose-dependent increases in heart rate and although cardiac output increased, cardiac power output remained unchanged as a consequence of the fall in peripheral resistance. The heart rate changes were blocked by metoprolol. Importantly, propranolol blocked both the heart rate response and the fall in peripheral resistance. 4. Isolated atrial strips showed a right shift of their dose-response curve to isoprenaline in the presence of the highly selective β₂-AR antagonist ICI 118 551 at concentrations above 1 × 10^?-⁸ mol/L. 5. We conclude that the sheep heart shows many pharmacological characteristics of the human heart which makes it a good pharmacological model in addition to its being amenable to many common techniques available for humans.     

In rats, oral oleoyl-DHEA is rapidly hydrolysed and converted to DHEA-sulphate

Background

In addition to the regulation of blood pressure, α₂- and β-adrenoceptor (AR) subtypes play an important role in the modulation of noradrenergic neurotransmission in the human CNS and PNS. Several studies suggest that the α₂-AR responsiveness in cells and tissues after chronic epinephrine (EPI) or norepinephrine (NE) exposure may vary, depending on the β-AR activity present there. Recently, we reported that in BE(2)-C human neuroblastoma cells (endogenously expressing α_2A- and β₂-AR), chronic EPI treatment (300 nM) produced a dramatic β-adrenoceptor-dependent desensitization of the α_2A-AR response. The aim of this study is to determine if stable addition of a β₂-AR to a second neuroblastoma cell line (SH-SY5Y), that normally expresses only α_2A-ARs that are not sensitive to 300 nM EPI exposure, would suddenly render α_2A-ARs in that cell line sensitive to treatment with the same EPI concentration.

Methods

These studies employed RT-PCR, receptor binding and inhibition of cAMP accumulation to confirm α₂-AR subtype expression. Stable clones of SH-SY5Y cells transfected to stably express functional β₂-ARs (SHβ₂AR4) were selected to compare sensitivity of α₂-AR to EPI in the presence or absence of β₂-ARs.

Results

A series of molecular, biochemical and pharmacological studies indicated that the difference between the cell lines could not be attributed to α₂-AR heterogeneity. We now report that after transfection of functional β₂-AR into SH-SY5Y cells (SHβ₂AR4), chronic treatment with modest levels of EPI desensitizes the α_2A-AR. This effect results from a β₂-AR dependent down-regulation of native α_2A-ARs by EPI accompanied by enhanced translocation of GRK2 and GRK3 to the membrane (required for GRK-mediated phosphorylation of agonist-occupied receptors).

Conclusion

This study further supports the hypothesis that the presence of the β-AR renders the α_2A-AR more susceptible to desensitization with physiological levels of EPI.     

β3-Adrenoceptor ligand development history through patent review

Introduction: Stimulation of the β₃-adrenoceptor (β₃-AR) is thought to be a valuable approach for the treatment of obesity, type 2 diabetes, heart failure, frequent urination, preterm labor, anxiety and depression. Therefore, the β₃-AR is recognized as an attractive target for drug discovery. Simultaneous activation of the β₁- and β₂-AR can cause undesirable side effects such as increased heart rate and muscle tremors. Consequently, much effort has been directed towards the design and development of selective β₃-AR agonists through original synthetic chemistry, extensive in vitro tests and detailed preclinical investigations to various phases of clinical trials.

Areas covered: SciFinder Scholar, PubMed, ISI web of Knowledge^SM, Espacenet, ClinicalTrials and Google have been used as the main sources for retrieving literature and patents filed since the discovery of β₃-AR through to June 2010. This review discusses the enormous efforts made by private and public research laboratories to uncover β₃-AR ligands and to prove their usefulness as drugs.

Expert opinion: Remarkable knowledge has been gained about the physio-pathological role of the β₃-AR to date. Many highly potent and selective β₃-AR ligands (agonists, antagonists and inverse agonists) have been discovered; however, further investigations are still needed to identify novel compounds acting as β₃-AR ligands in order to adequately treat the diseases in which β₃-AR is involved.     

Reciprocal regulation between M3 muscarinic acetylcholine receptor and protein kinase C-ε in ventricular myocytes during myocardial ischemia in rats

We have studied the association between M₃ muscarinic acetylcholine receptors (M₃-mAChR) and protein kinase C-ε (PKC-ε) during ischemic myocardial injury using Western blot analysis and immunoprecipitation technique. Myocardial ischemia (MI) induced PKC-ε translocation from cytosolic to membrane fractions. This translocation participated in the phosphorylation of M₃-mAChR in membrane fractions, which could be abolished by the inhibitor of PKC, chelerythrine chloride. On the other hand, M₃-mAChR could also regulate the expression of PKC-ε in ischemic myocardium. Choline (choline chloride, an M₃ receptor agonist, administered at 15 min before occlusion) strengthened the association between PKC-ε and M₃-mAChR. However, blockade of M₃-mAChR by 4-diphenylacetoxy-N-methylpiperidine methiodide (an M₃ receptor antagonist, administered at 20 min before occlusion) completely inhibited the effect of choline on the expression of PKC-ε. We conclude that the translocation of PKC-ε is required for the phosphorylation of M₃-mAChR; moreover, increased PKC-ε activity is associated with M₃-mAChR during MI. This reciprocal regulation is likely to play a role in heart signal transduction during ischemia between ventricular myocytes.     

Selective α1B- and α1D-adrenoceptor antagonists suppress noradrenaline-induced activation,proliferation and ECM secretion of rat hepatic stellate cells in vitro

Aim:

To explore the effects of noradrenaline (NA) on hepatic stellate cells (HSCs) in vitro and to determine the adrenoceptor (AR) subtypes and underlying mechanisms.

Methods:

The distribution and expressions of α_1A-, α_1B-, and α_1D-ARs in HSC-T6 cells were analyzed using immunocytochemistry and RT-PCR. Cell proliferation was evaluated with MTT assay. The expression of HSC activation factors [transforming factor-β₁ (TGF-β₁) and α-smooth muscle actin (α-SMA)], extracellular matrix (ECM) secretion factors [tissue inhibitor of metalloproteinase-1 (TIMP-1) and collagen-Ι (ColΙ)] and PKC-PI3K-AKT signaling components (PKC, PI3K, and AKT) in the cells were detected by Western blotting and RT-PCR.

Results:

Both α_1B- and α_1D-AR were expressed in the membrane of HSC-T6 cells, whereas α_1A-AR was not detected. Treatment of the cells with NA concentration-dependently increased cell proliferation (EC₅₀=277 nmol/L), which was suppressed by the α_1B-AR antagonist CEC or by the α_1D-AR antagonist BMY7378. Furthermore, NA (0.001, 0.1, and 10 μmol/L) concentration-dependently increased the expression of TGF-β₁, α-SMA, TIMP-1 and ColΙ, PKC and PI3K, and phosphorylation of AKT in HSC-T6 cells, which were suppressed by CEC or BMY7378, or by pertussis toxin (PT), RO-32-0432 (PKC antagonist), {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 (PI3K antagonist) or GSK690693 (AKT antagonist).

Conclusion:

NA promotes HSC-T6 cell activation, proliferation and secretion of ECM in vitro via activation of G_α-coupled α_1B-AR and α_1D-AR and the PKC-PI3K-AKT signaling pathway.     

Pro-apoptotic effect of anti-β1-adrenergic receptor antibodies in periodontitis patients

An anti-β₁-adrenergic antibody from the sera of periodontitis patients (anti-β₁-AR IgG) against the second extracellular loop of the human β₁-adrenoceptor (β₁-AR) has been shown to cause rat atria apoptosis. The anti-β₁-AR IgG binds and activates atria β₁-AR, increasing the intracellular calcium concentration, which, in turn, activates caspases-3, -8, and -9. The β₁-AR and the post-receptor activation of calcium/calmodulin (CaM) lead to increased inducible nitric oxide synthase (iNOS) activity, with an increase in cyclic GMP (cGMP) accumulation as well as increased JNK phosphorylation and cyclic AMP (cAMP) production. We also observed an apoptotic effect of anti-β₁-AR IgG, with increased generation of PGE₂. Comparatively, xamoterol, an authentic β₁-AR agonist, mimicked the autoantibody effect on rat atria β₁-AR apoptosis. Our results suggest that autoantibodies from the sera of periodontitis patients bind and interact with rat atria β₁-AR, provoking apoptosis. This implicates a series of modulatory cardiac signaling events that could alter normal heart function and may occur with chronic stimulation of the atria β₁-AR, which could lead to heart failure. These results suggest an important link between periodontitis and cardiovascular disease.     

Protein kinase C isozymes in prostatic epithelial cells from normal,diabetic and insulin-treated diabetic rats

• 1.1. Immunoblot experiments in rat prostatic epithelium using a non-selective antibody against protein kinase C (PKC) allowed to detect three PKC subspecies of 87.5, 55.5 and 34.6 kDa that showed higher, similar and lower immunoreactivity in the membrane than in the cytosolic compartment, respectively.
• 2.2. Specific monoclonal antisera revealed that the PKC-γ isozyme is not expressed in the rat prostatic epithelium, whereas the PKC-β isozyme was noted only in the cytosolic fraction showing an apparent molecular weight of 75.5 kDa.
• 3.3. Induction of diabetes by streptozotocin led to modifications in the expression of PKC isozymes so that the immunoreactivities of the 87.5- and 55.5-kDa PKC forms decreased in both cytosolic and membrane subcellular fractions to different extents.
• 4.4. The most important decrease was that of the 55.5-kDa PKC form in cytosol that returned to control values by insulin therapy, whereas PKC-β suffered also some decrease in diabetes and increased again with insulin treatment.

     

Relation between β-adrenoceptor stimulation and nitric oxide synthesis in vascular control

This commentary reviews recent evidence that implicates nitric oxide (NO) as a mediator of β₂-adrenoceptor (β₂-AR)-initiated vasodilatation. Emphasis is placed on the following: 1) in vivo studies that demonstrate potential physiological importance, 2) mechanistic studies performed in vitro in human umbilical vein endothelial cells (HUVEC), 3) effects of β₂ agonists on arterial pulse wave reflection, and 4) therapeutic opportunities offered by the combination of β₂ agonist action with selective β₁ antagonism. Vascular β₂-AR-initiated mechanisms provide a physiologically important control mechanism during exercise. Activation of β₂-AR in HUVEC leads to vasodilatation that is partly NO-mediated via activation of protein kinase A (PKA) and of phosphatidylinositol-3 kinase (PI3K)/Akt pathways, leading to serine phosphorylation of the endothelial NO synthase (eNOS). In vivo, β₂-AR activation limits the rise in blood pressure during exercise and reduces arterial pulse wave reflection. Nebivolol is a selective β₁-AR antagonist with vasodilator actions operating through these pathways, offering novel therapeutic opportunities.

     

Effect of glipizide GITS on insulin sensitivity,glycemic indices,and abdominal fat composition in NIDDM

Glipizide in a once daily formulation utilizing the gastrointestinal therapeutic system (GITS) has been shown in preliminary studies to improve insulin sensitivity as assessed with meal tolerance testing. To evaluate the ability of glipizide GITS to specifically improve clinical insulin sensitivity in vivo, a double–blind, placebo-controlled trial randomized 40 NIDDM subjects to either glipizide GITS or placebo. The study was designed to evaluate NIDDM subjects whose fasting blood glucose was <190 mg% and Ghb <11% to avoid the adverse effects of hyperglycemia on insulin resistance and secretion. After screening, oral hypoglycemic agents were discontinued for one month, at which time a meal tolerance test with glucose and insulin response, glycated hemoglobin, and fructosamine were obtained. Insulin sensitivity (S_I) and glucose effectiveness (S_g) were determined with a 4–h frequently sampled intravenous tolerance test (modified minimal model – 3rd phase insulin infusion) at baseline. Specific abdominal fat depots were quantitated by MRI scans. Patients were then randomized to receive placebo or active drug and all parameters were repeated at 1, 2, 5, and 8 months after randomization. Glipizide GITS significantly improved meal tolerance, reduced glycated blood proteins, and increased insulin sensitivity (P < .001). No change was seen for S_G. There was no significant change in abdominal fat distribution during the trial. Glipizide GITS is effective in lowering glucose tolerance and improving insulin sensitivity without an increase in fasting insulin, weight gain, or change in abdominal fat composition. Drug Dev. Res. 44:1–7, 1998. © 1998 Wiley-Liss, Inc.     

The time course of cardioprotection induced by GR79236, a selective adenosine A1-receptor agonist, in myocardial ischaemia-reperfusion injury in the pig

The cardioprotective effects of the selective adenosine A1-receptor agonist, GR79236 (N-[(1S, trans)-2-hydroxycyclopentyl]adenosine), were examined in a porcine model of myocardial ischaemia-reperfusion injury. When pigs were subjected to a 50-min coronary artery occlusion followed by 3-h reperfusion, GR79236 (10 nmol/kg, i.v.) significantly reduced infarct size whether given 10 min before the onset of ischaemia or reperfusion. This effect was independent of the bradycardia induced by GR79236, as it was also observed in animals in which heart rate was maintained by electrical pacing. However, GR79236 administered 10 min after reperfusion did not reduce infarct size. GR79236 had no effect on the incidence or outcome of ventricular dysrhythmias in this pig model of infarction. Similarly, ischaemic preconditioning (IPC, 2 x 10-min ischaemia and 10-min reperfusion) significantly reduced infarct size. The selective adenosine A1-receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 3.3 micromol/kg, i.v.), abolished the haemodynamic and cardioprotective effects of GR79236 and the cardioprotective effects of IPC in anaesthetised pigs. In conclusion, GR79236 exerted a marked cardioprotective effect in a porcine model of myocardial ischaemia-reperfusion injury, provided that it was administered before reperfusion. This suggests that GR79236 may have clinical utility in the treatment of various aspects of ischaemic heart disease.     

二苯乙烯类化合物E1的降糖作用及其机制的初步研究

目的　观察灌胃给予二苯乙烯类化合物E1对实验性非胰岛素依赖性糖尿病 (NIDDM )大鼠的降糖作用。方法　通过尾静脉注射小剂量链佐菌素 (streptozotocin ,STZ)来损伤大鼠胰岛细胞造成其糖耐量异常 ,继而喂以高糖 -高脂饲料来诱发动物肥胖形成的Ⅱ型糖尿病大鼠模型。结果　灌胃给予二苯乙烯类化合物E1能明显降低NIDDM大鼠空腹血糖、葡萄糖耐量实验 (OGTT)各时间点的血糖值 ;二苯乙烯类化合物E1.0 1mmol·L-1及 0 0 0 1mmol·L-1对βTC3 细胞无刺激其分泌胰岛素作用。结论　二苯乙烯类化合物E1的降糖作用并非通过刺激胰岛素的分泌 ,而可能是通过增加胰岛素作用效率     

Effect of Lycium barbarum polysaccharide on the improvement of insulin resistance in NIDDM rats

Lycium barbarum is one of the traditional oriental medicines. It has been reported to reduce blood glucose levels. In this study, the effect of Lycium barbarum polysaccharide (LBP) on the improvement of insulin resistance and lipid profile was studied in rats, a model for non-insulin dependent diabetes mellitus (NIDDM). The rats were divided into three groups: control, NIDDM control, and NIDDM+LBP. Diabetes model groups were made by feeding high-fat diet and subjecting to i.p. streptozotocin (50 mg/kg). LBP treatment for 3 weeks resulted in a significant decrease in the concentration of plasma triglyceride and weight in NIDDM rats. Furthermore, LBP markedly decreased the plasma cholesterol levels and fasting plasma insulin levels, and the postprandial glucose level at 30 min during oral glucose tolerance test and significantly increased the Insulin Sensitive Index in NIDDM rats. In the present study, we have tested that LBP can alleviate insulin resistance and the effect of LBP is associated with increasing cell-surface level of glucose transporter 4 (GLUT4) in skeletal muscle of NIDDM rats. Under insulin stimulus, GLUT4 content in plasma membrane in NIDDM control rats was significantly lower than that of control (p<0.01), and GLUT4 content in the plasma membrane in NIDDM+LBP rats was higher than that of NIDDM control rats (p<0.01). In conclusion, LBP can ameliorate insulin resistance, and the mechanism may be involved in increasing cell-surface level of GLUT4, improving GLUT4 trafficking and intracellular insulin signaling.