endothelin-1 and Hyperinsulinism

Two syndromes are called syndromes X: cardiac (effort anginal pain, positive exercise tolerance test and absence of angiographically documented critical stenosis in coronary arteries) and metabolic (according to WHO definition: impaired glucose tolerance and insulin resistance and > or = 2 risk factors from the following list: hypertension, dyslipidaemia, visceral obesity and microalbuminuria). Hyperinsulinaemia and endothelial dysfunction are present in both syndromes. The contribution of endothelial nitric oxide synthase gene mutations to the etiology of these syndromes is also studied. Several mechanisms may be involved in the development of endothelial dysfunction, such as reduced synthesis and release of nitric oxide (NO), enhanced inactivation of NO after its release from endothelial cells or enhanced synthesis of vasoconstricting agents. It has been demonstrated that insulin exerts a direct hypertrophic effect on the vascular endothelium and the smooth muscle cells. The hemodynamic properties of insulin have also been discussed. Some findings suggest that in the skeletal muscle circulation, insulin stimulates both endothelin-1 (ET-1) and nitric oxide activity and an imbalance between the release of these two substances may be involved in the pathophysiology of endothelial dysfunction.

Topics: Albuminuria; Endothelin-1; Humans; Hyperinsulinism; Hyperlipidemias; Hypertension; Insulin; Metabolic Syndrome; Microvascular Angina; Mutation; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Obesity; Risk Factors

Endogenous endothelin action is augmented in human obesity and type 2 diabetes and contributes to endothelial dysfunction and impairs insulin-mediated vasodilation in humans. We hypothesized that insulin resistance-associated hyperinsulinemia could preferentially drive endothelin-mediated vasoconstriction. We applied hyperinsulinemic-euglycemic clamps with higher insulin dosing in obese subjects than lean subjects (30 vs. 10 mU.m(-2).min(-1), respectively), with the goal of matching insulin's nitric oxide (NO)-mediated vascular effects. We predicted that, under these circumstances, insulin-stimulated endothelin-1 (ET-1) action (assessed with the type A endothelin receptor antagonist BQ-123) would be augmented in proportion to hyperinsulinemia. NO bioactivity was assessed using the nitric oxide synthase inhibitor N(G)-monomethyl-l-arginine. Insulin-mediated vasodilation and insulin-stimulated NO bioavailability were well matched across groups by this approach. As expected, steady-state insulin levels were approximately threefold higher in obese than lean subjects (109.2 +/- 10.2 pmol/l vs. 518.4 +/- 84.0, P = 0.03). Despite this, the augmentation of insulin-mediated vasodilation by BQ-123 was not different between groups. ET-1 flux across the leg was not augmented by insulin alone but was increased with the addition of BQ-123 to insulin (P = 0.01 BQ-123 effect, P = not significant comparing groups). Endothelin antagonism augmented insulin-stimulated NO bioavailability and NOx flux, but not differently between groups and not proportional to hyperinsulinemia. These findings do not support the hypothesis that insulin resistance-associated hyperinsulinemia preferentially drives endothelin-mediated vasoconstriction.

Topics: Adult; Antihypertensive Agents; Endothelin Receptor Antagonists; Endothelin-1; Female; Humans; Hyperinsulinism; Insulin; Male; Muscle, Skeletal; Nitric Oxide; Obesity; omega-N-Methylarginine; Peptides, Cyclic; Vasoconstriction

Cardiovascular diseases are characterized by insulin resistance and elevated endothelin (ET)-1 levels. Furthermore, ET-1 induces insulin resistance. To elucidate this mechanism, six healthy subjects were studied during a hyperinsulinemic euglycemic clamp during infusion of (the ET-1 precursor) big ET-1 alone or after ET(A)- or ET(B)-receptor blockade. Insulin levels rose after big ET-1 with or without the ET(B) antagonist BQ-788 (P < 0.05) but were unchanged after the ET(A) antagonist BQ-123 + big ET-1. Infused glucose divided by insulin fell after big ET-1 with or without BQ-788 (P < 0.05). Insulin and infused glucose divided by insulin values were normalized by ET(A) blockade. Mean arterial blood pressure rose during big ET-1 with or without BQ-788 (P < 0.001) but was unchanged after BQ-123. Skeletal muscle, splanchnic, and renal blood flow responses to big ET-1 were abolished by BQ-123. ET-1 levels rose after big ET-1 (P < 0.01) in a similar way after BQ-123 or BQ-788, despite higher elimination capacity after ET(A) blockade. In conclusion, ET-1-induced reduction in insulin sensitivity and clearance as well as splanchnic and renal vasoconstriction are ET(A) mediated. ET(A)-receptor stimulation seems to inhibit the conversion of big ET-1 to ET-1.

Topics: Adult; Antihypertensive Agents; Arteries; Blood Glucose; Blood Pressure; Endothelin Receptor Antagonists; Endothelin-1; Endothelins; Heart Rate; Hepatic Veins; Humans; Hyperinsulinism; Insulin Resistance; Male; Muscle, Skeletal; Oxygen; Peptides, Cyclic; Protein Precursors; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Renal Circulation; Splanchnic Circulation

Cold- and insulin-mediated release of angiotensin II (AII) and endothelin-1 (ET-1), as well as vascular reactivity to exogenous ET-1 and to insulin, were compared in hypertensive and normotensive subjects. Peripheral vascular release of AII and of ET-1 was investigated in 10 hypertensive (H; 29.2+/-5.8 years) and 12 normotensive (N; 29.1+/-4.6 years) men in two separate trials. Net transfemoral balance of AII and of ET-1 was calculated from the respective Arterio-Venous (A-V) differences in plasma concentrations (PC) of the peptides and the regional plasma flow (indocyanine-green dye method), both at baseline conditions and after a cold stimulus (immersion of one hand into ice water) in 7H and 6N, or during short-time hyperinsulinemia (hyperinsulinemic euglycemic clamp: biosynthetic human insulin, 1 mU/kg/min) in 7H and 7N. Moreover, hemodynamic changes to sequential exogenous ET-1 infusion (1, 2.5, 5, 10, 20, 40 ng/min) or during hyperinsulinemic clamp were studied in 7H and 6N and 7H and 7N, respectively. Baseline net-transfemoral balance of ET-1 and of AII were similar in the two subject groups. The cold stimulus provoked a similar increase in transfemoral ET-1 release in H and N (H: 257.0+/-31.7 to 526.2+/-393.7 pg/min; N: 280.2+/-112.7 to 524.0+/-393.7 pg/min, mean +/- SD, P<.05). In contrast, the cold-induced increase in transfemoral AII release was somewhat more pronounced in H than in N (H: 162.2+/-304.6 to 1081.7+/-1037.7 pg/ min, P<.05; N: 83.9+/-166.3 to 317.6+/-187.8 pg/ min, P<.02; maximum value H v. N P<.05). During the hyperinsulinemic clamp the PC of insulin increased from 5.8+/-2.8 to 69.1+/-15.5 microU/ mL in H and from 4.6+/-1.7 to 67.5+/-9,5 microU/mL in N; P<.0005. Hyperinsulinemia induced a similar elevation of norepinephrine PC in H and N, but an increase in transfemoral ET-1 release in N only (219.7+/-161.2 to 512.2+/-279.0 pg/min, P<.02). In contrast, hyperinsulinemia increased transfemoral AII formation in H (730.4+/-554.3 to 1088.6+/-597.9 pg/min, P<.05), but not in N. Insulin-mediated vasodilation was observed only in N, whereas ET-1-induced vasoconstriction was blunted in H. We conclude that the cold-induced increase in peripheral vascular release of AII is more pronounced in H than in N, whereas insulin provokes an increase in AII formation in hypertensives only. Moreover, insulin-mediated vasodilation and ET-1-dependent vasoconstriction are blunted in hypertensive subjects.

Topics: Adult; Angiotensin II; Blood Glucose; Cold Temperature; Endothelin-1; Endothelium, Vascular; Femoral Artery; Glucose Clamp Technique; Humans; Hyperinsulinism; Hypertension; Indocyanine Green; Insulin; Male; Norepinephrine; Pilot Projects; Vascular Resistance; Vasoconstrictor Agents

Insulin and angiotensin II (Ang II) are involved in the regulation of endothelin-1 (ET-1). This study investigates their possible influence on plasma levels of ET-1 in humans. Twenty patients with essential hypertension were included in a randomized, double-blind, placebo-controlled crossover study of 4 weeks' treatment with losartan, a selective type 1 angiotensin (AT1) receptor antagonist. The effect was evaluated in the fasting state and during acute hyperinsulinemia physiologically induced by oral glucose ingestion (OGTT) and by euglycemic glucose clamp. Losartan lowered blood pressure significantly, but did not influence plasma levels of ET-1 in the fasting condition (5.2 +/- 0.2 fmol/mL on placebo and 5.6 +/- 0.3 fmol/mL after losartan treatment). During both models of acute hyperinsulinemia, there was a significant decrease in plasma ET-1. In the OGTT the mean values after placebo treatment decreased from 5.2 +/- 0.2 fmol/mL at time 0 to 4.7 +/- 0.4 (P = .001) and 4.0 +/- 0.5 (P = .001) at 60 and 120 minutes, respectively. During the clamp the mean ET-1 values decreased from 5.7 +/- 0.4 fmol/mL at time 0 to 4.6 +/- 0.2 (P < .001) and 4.3 +/- 0.3 (P = .006) at 60 and 120 minutes, respectively. No differences in these profiles occurred after losartan treatment. Significant inverse correlation between fasting levels of ET-1 and insulin sensitivity index was found, r = -.51, P = .003. In conclusion, losartan did not influence the circulating levels of ET-1 in basal condition or during acute hyperinsulinemia, whereas a significant decrease in plasma ET-1 occurred during acute hyperinsulinemia. A significant inverse correlation demonstrated between basal levels of plasma ET-1 and the insulin-stimulated glucose uptake could point to a possible regulatory influence of ET-1 production on glucose metabolism or vice versa.

Topics: Adult; Aged; Antihypertensive Agents; Cross-Over Studies; Double-Blind Method; Endothelin-1; Fasting; Female; Glucose Clamp Technique; Glucose Tolerance Test; Humans; Hyperinsulinism; Hypertension; Kinetics; Losartan; Male; Middle Aged; Placebos

Impaired glucose tolerance (IGT) is an important prediabetic stage characterized by elevated concentrations of glucose and insulin in the blood. The pathological hyperglycemia and hyperinsulinemia in IGT may regulate the expression of microRNA-21 (miR-21) and affect the downstream insulin signaling pathways, leading to endothelial cell dysfunction and early renal damage.. The individual and combined effects of insulin and glucose were investigated using human glomerular endothelial cells (HGECs). The expression levels of miR-21, and PTEN/AKT/eNOS and MAPK/ET-1 pathway proteins in the treated cells were measured. The levels of nitric oxide (NO) and endothelin-1 (ET-1) secreted by the cells were also measured. The role of miR-21 in mediating the regulatory effects of insulin and glucose was assessed by overexpression/inhibition of this miRNA using mimics/inhibitor.. High (>16.7 mmol/L) concentration of glucose upregulated the expression of miR-21, leading to the activation and inhibition of the PTEN/AKT/eNOS and MAPK/ET-1 pathways, and upregulation of NO and downregulation of ET-1 secretion, respectively. High (>25 ng/mL) concentration of insulin downregulated the expression of miR-21, and lead to the activation of the MAPK/ET-1 and inhibition of the PTEN/AKT/eNOS pathway, thereby upregulating the expression of ET-1 and downregulating the secretion of NO. MiR-21 was observed to play a key role by directly controlling the activation of the insulin signaling pathways when the cells were cotreated with different concentrations of insulin and glucose. The expression of miR-21 was found to be dependent on the relative concentration of insulin and glucose. Under simulated conditions of the IGT stage (8.3 mmol/L glucose + 50 ng/mL insulin), the inhibitory effect of high insulin concentration on miR-21 expression in the cells attenuated the activation by high glucose concentration, resulting in the downregulation of miR-21, upregulation of ET-1 and downregulation of NO secretion.. Taken together, these results indicate that high insulin and glucose concentrations regulate the secretory function of glomerular endothelial cells in opposite ways by regulating the expression of miRNA-21. Pathological concentrations of insulin and glucose in the IGT stage may lead to a decrease in miR-21 expression, thereby disordering the secretion of vasoactive factors, resulting in renal tubule ischemia.

Topics: Endothelial Cells; Endothelin-1; Endothelium, Vascular; Glucose Intolerance; Glucose Tolerance Test; Humans; Hyperglycemia; Hyperinsulinism; Insulin; MicroRNAs; Nitric Oxide; Nitric Oxide Synthase Type III; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; PTEN Phosphohydrolase; Signal Transduction

Fructose administration can induce hypertension, insulin resistance and hypertriglyceridemia. Here, we investigated the possible protective effect of infliximab (IFX), a tumor necrosis factor alpha (TNF-α) inhibitor, or tocilizumab (TOC), an interleukin-6 (IL6) inhibitor, on fructose-induced increase in blood pressure, insulin resistance and hyperlipidemia in rats. The animals were fed a 60% fructose diet in the absence or presence of IFX (5 mg/kg, i.p., once weekly) or TOC (8 mg/kg, i.p., once every two weeks). Fructose significantly increased blood pressure, heart rate and homeostatic model assessment of insulin resistance (HOMA-IR). Fructose also significantly raised the concentrations of fasting plasma insulin, triglycerides, total cholesterol, uric acid, tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), malondialdhyde (MDA) and nitric oxide. Fructose also significantly decreased plasma superoxide dismutase (SOD) and catalase activities. In addition, fructose significantly increased aortic endothelin and nitric oxide concentrations. Both IFX and TOC attenuated the fructose-induced increase in blood pressure, insulin resistance, and the concentrations of uric acid, MDA and IL-6. TOC significantly reduced fructose-induced increase in triglycerides and cholesterol. In addition, IFX increased plasma SOD and catalase activities. Our results showed that both IFX and TOC were partially successful in reversing fructose - induced changes.

Topics: Animals; Antibodies, Monoclonal, Humanized; Aorta; Biomarkers; Blood Glucose; Blood Pressure; Catalase; Cholesterol; Endothelin-1; Fructose; Heart Rate; Hyperinsulinism; Hypertension; Inflammation Mediators; Infliximab; Insulin; Male; Malondialdehyde; Nitric Oxide; Oxidative Stress; Rats, Wistar; Superoxide Dismutase; Triglycerides

Topics: Adult; Arterioles; Cross-Sectional Studies; Diabetes Mellitus, Type 2; Endothelin-1; Female; Humans; Hyperinsulinism; Insulin; Middle Aged; Muscle, Skeletal; Nitric Oxide; Nitric Oxide Synthase Type III; Obesity; Vasoconstriction; Vasodilation

Cumulative evidence suggests that moderate red wine consumption protects the cardiovascular system. The effect of cultured cells derived from red grape berry (RGC) on blood pressure (BP) has not been investigated. We therefore studied the antihypertensive effects of oral consumption of RGC in experimental rat model of metabolic-like syndrome and assessed its effect on human umbilical vein endothelial cells (HUVECs).. Forty male Sprague-Dawley rats were fed for 5 weeks with either a high fructose diet (HFD) (n = 10) or HFD supplemented, during the last 2 weeks, with different doses (200, 400 and 800 mg/kg/day) of RGC suspended in their food (n = 30). BP, plasma triglycerides, insulin and adiponectin levels were measured at the beginning and after 3 and 5 weeks of diet. RGC effect on vasodilatation was evaluated by its ability to affect endothelin-1 (ET-1) production and endothelial nitric oxide synthase (eNOS) expression in HUVECs.. BP, plasma triglycerides, insulin and adiponectin increased significantly in rats fed with a HFD. The increase in BP, plasma triglycerides and insulin was attenuated by RGC supplementation. Incubation of HUVECs with RGC demonstrated a concentration-dependent inhibition of ET-1 secretion and increase in the level of eNOS, signaling a positive effect of RGC on vasodilatation.. In rats with metabolic-like syndrome, RGC decreased BP and improved metabolic parameters. These beneficial effects may be mediated by the cell constituents, highly rich with polyphenols and resveratrol, reside in their natural state.

Topics: Animals; Antihypertensive Agents; Cells, Cultured; Dietary Supplements; Endothelin-1; Fruit; Human Umbilical Vein Endothelial Cells; Humans; Hyperinsulinism; Hypertension; Hypertriglyceridemia; Hypolipidemic Agents; Male; Metabolic Syndrome; Nitric Oxide Synthase Type III; Pigments, Biological; Plant Extracts; Rats, Sprague-Dawley; Vasodilator Agents; Vitis

Insulin leads to overexpression of endothelin-1 (ET-1) in the endothelium of insulin-resistant rodents. If this is also the case in equine laminar tissue, this could explain the predisposition of insulin-resistant horses to laminitis.. To investigate the effect of hyperinsulinaemia on metabolism and vascular resistance of the isolated equine digit in a model of extracorporeal perfusion.. Randomised, controlled study with interventional group, with blinded evaluation of histology results.. After exsanguination, equine digits (n = 11) and autologous blood were collected at an abattoir. One digit served as a hyperinsulinaemic pilot limb, 5 digits were assigned to the hyperinsulinaemic perfusion (IP) group and 5 to the control perfusion (CP) group. Digits were perfused for 10 h at a defined perfusion rate of 12 ml/min/kg. After the first hour of perfusion (equilibration period), insulin was added to the reservoir of the IP digits. Perfusion pressure, glucose consumption, lactate and lactate dehydrogenase were monitored. Vascular resistance was calculated as perfusion pressure (in millimetres of mercury) in relation to the flow rate (in millilitres per minute). After perfusion, histology samples of the dorsal hoof wall (haematoxylin & eosin or periodic acid-Schiff) were evaluated. Immunohistology with a polyclonal rabbit-derived anti-endothelin antibody was used for detection of ET-1.. In the IP group, the mean insulin concentration in the plasma of the perfusate was 142 ± 81 μiu/ml, while insulin concentration was <3 μiu/ml in the CP group. Mean vascular resistance was significantly higher (P<0.01) in the IP group (2.04 ± 1.13 mmHg/ml/min) than in the CP group (1.31 ± 0.55 mmHg/ml/min). Histology of the IP group samples showed significantly more vessels with an open lumen, increased width of the secondary epidermal lamellae and formation of oedema. In the lamellar vessels (veins and arteries) and nerve fibres, ET-1 expression was much more prominent in the IP group than in the CP group samples.. Short-term hyperinsulinaemia leads to increased vascular resistance in the equine digit and increased expression of ET-1 in the laminar tissue.

Topics: Animals; Cadaver; Endothelin-1; Gene Expression Regulation; Horses; Hyperinsulinism; Insulin; Perfusion

Rosmarinic acid (RA), a caffeic acid ester, has insulin-sensitizing and antioxidant effects in high fructose-fed model of insulin resistance (IR). This study investigated whether RA supplementation prevents cardiac abnormalities and hypertension in fructose-fed rats (FFR). Rats fed with fructose diet (60 g/100 g) for 60 days exhibited metabolic abnormalities and rise in plasma and cardiac lipids and whole body IR. The levels of cardiac antioxidants and plasma ferric reducing antioxidant power were significantly reduced in FFR concomitant with increased levels of lipid peroxidation and protein oxidation products. A significant rise in troponin T, creatine kinase-MB, aspartate transaminase, and lactate dehydrogenase in plasma of FFR was noted. RA supplementation to FFR (10 mg/kg from the 16th day) significantly improved insulin sensitivity, reduced lipid levels, oxidative damage, and the expression of p22phox subunit of nicotinamide adenine dinucleotide phosphate reduced oxidase, and prevented cardiac hypertrophy. Fructose-induced rise in blood pressure was also lowered by RA through decrease in endothelin-1 and angiotensin-converting enzyme activity and increase in nitric oxide levels. Histology revealed a reduction in myocardial damage in RA-supplemented FFR. These findings suggest that RA acts as a vasoactive substance and a cardioprotector through its antioxidant property. Thus, RA may be useful in reducing the cardiovascular risk associated with IR.

Topics: Animals; Antioxidants; Aspartate Aminotransferases; Blood Glucose; Blood Pressure; Body Weight; Cinnamates; Creatine Kinase, MB Form; Depsides; Dietary Carbohydrates; Endothelin-1; Fructose; Gene Expression; Heart; Hyperinsulinism; Hypertension; Insulin; Insulin Resistance; Kallikreins; L-Lactate Dehydrogenase; Lipid Metabolism; Lipids; Male; Myocardium; NADPH Oxidases; Nitrates; Nitric Oxide Synthase Type III; Organ Size; Oxidative Stress; Peptidyl-Dipeptidase A; Rats; Rats, Wistar; Rosmarinic Acid; Troponin C

Hypoglycemia is associated with increased cardiovascular mortality, but the reason for this association is poorly understood. We tested the hypothesis that the myocardial blood flow reserve (MBFR) is decreased during hypoglycemia using myocardial contrast echocardiography in patients with type 1 diabetes mellitus (DM) and in healthy control subjects.. Twenty-eight volunteers with DM and 19 control subjects underwent hyperinsulinemic clamps with maintained sequential hyperinsulinemic euglycemia (plasma glucose, 90 mg/dL [5.0 mmol/L]) followed by hyperinsulinemic hypoglycemia (plasma glucose, 50 mg/dL [2.8 mmol/L]) for 60 minutes each. Low-power real-time myocardial contrast echocardiography was performed with flash impulse imaging using low-dose dipyridamole stress at baseline and during hyperinsulinemic euglycemia and hyperinsulinemic hypoglycemia. In control subjects, MBFR increased during hyperinsulinemic euglycemia by 0.57 U (22%) above baseline (B coefficient, 0.57; 95% confidence interval, 0.38 to 0.75; P<0.0001) and decreased during hyperinsulinemic hypoglycemia by 0.36 U (14%) below baseline values (B coefficient, -0.36; 95% confidence interval, -0.50 to -0.23; P<0.0001). Although MBFR was lower in patients with DM at baseline by 0.37 U (14%; B coefficient, -0.37; 95% confidence interval, -0.55 to -0.19; P=0.0002) compared with control subjects at baseline, the subsequent changes in MBFR during hyperinsulinemic euglycemia and hyperinsulinemic hypoglycemia in DM patients were similar to that observed in control subjects. Finally, the presence of microvascular complications in the patients with DM was associated with a reduction in MBFR of 0.52 U (24%; B coefficient, -0.52; 95% confidence interval, -0.70 to -0.34; P<0.0001).. Hypoglycemia decreases MBFR in both healthy humans and patients with DM. This finding may explain the association between hypoglycemia and increased cardiovascular mortality in susceptible individuals.

Topics: Acute Disease; Adult; Blood Glucose; C-Reactive Protein; Coronary Circulation; Diabetes Mellitus, Type 1; Echocardiography; Endothelin-1; Epinephrine; Female; Glucose Clamp Technique; Humans; Hyperinsulinism; Hypoglycemia; Insulin; Male; Microbubbles; Single-Blind Method; Young Adult

Endothelial dysfunction and decreased production of nitric oxide (NO) by endothelial NO synthase (eNOS) are implicated in the pathogenesis of hypertension and insulin resistance. Because the potential influence of increased eNOS expression/activity on these parameters is unclear, the present study examined the effects of eNOS gene therapy on insulin resistance and blood pressure alterations in a fructose-induced hypertension model in rats. As predicted, 2 weeks of fructose consumption in the drinking water resulted in elevated systolic blood pressure and insulin resistance. These and other physiologic alterations were reversed within 2 weeks after a single intravenous injection of a vector containing the human eNOS cDNA (pcDNA3.1-eNOS), whereas injection of an empty vector (pcDNA3.1) was without effect. In support of the beneficial effects of pcDNA3.1-eNOS treatment being because of enhanced eNOS expression and activity, increased eNOS protein levels were documented in aorta, liver, kidney, and heart of fructose-treated rats injected with pcDNA3.1-eNOS, and corresponding elevations in nitrite/nitrate and cGMP concentrations were observed in urine. Furthermore, pcDNA3.1-eNOS treatment prevented fructose-induced decreases in expression levels of insulin receptor substrate-1, the p110 catalytic subunit of phosphatidylinositol 3-kinase, phosphorylated Akt, and phosphorylated AMP-activated protein kinases in liver, aorta, and skeletal muscle. The results of this study cumulatively indicate that gene therapy with human eNOS decreased fructose-induced hypertension and insulin resistance in rats and suggest potential signaling pathways that mediate these effects. These data highlight the potential utility of eNOS gene therapy in the treatment of hypertension and insulin resistance.

Topics: AMP-Activated Protein Kinase Kinases; Animals; Endothelin-1; Fructose; Gene Expression; Gene Transfer Techniques; Humans; Hyperinsulinism; Hypertension; Insulin; Male; Mitogen-Activated Protein Kinase 1; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Protein Kinases; Rats; Rats, Sprague-Dawley; RNA, Messenger; Urine

To estimate the influence of anthocyanins from Aronia melanocarpa on blood pressure, concentration of endothelin-1 (ET-1), serum lipids, fasting glucose, uric acid and membrane cholesterol in erythrocytes of patients (pts) with metabolic syndrome (MS).. The study comprised 22 healthy volunteers and 25 pts with MS treated with anthocyanins (3 x 100 mg/d) for 2 months. Waist circumference (> or = 80 cm for women and > or =94 cm for men), triglicerydes (TG) level >150 mg/dl (1.7 mmol/l), cholesterol-HDL (HDL-C) level < 40 mg/dl (1.0 mmol/l) for men and <50 mg/dl (1.3 mmol/l) for women, systolic blood pressure (SBP) >130 mmHg and/or diastolic blood pressure (DBP) >85 mmHg were inclusion criteria for patients with MS. Before and after 2 months of treatment the following parameters were determined: SBP, DBP, serum lipids (total cholesterol--TC, cholesterol LDL--LDL-C, cholesterol HDL--HDL-C, TG--by enzymatic method), membrane cholesterol in erythrocytes (method of IIcy), ET-1 (immunoenzymatic method), fasting glucose level was (colorimetric method), uric acid (enzymatic--colorimetric method).. After two months therapy of anthocyanins from Aronia melanocarpa in comparison with baseline it was observed a significant decrease of: SBP (144.20 +/- 9.97 vs. 131.83 +/- 12.24 mmHg, p < 0.001) and DBP (87.20 +/- 9.9 vs. 82.13 +/- 10.33 mmHg, p < 0.05), TC (242.80 +/- 34.48 vs. 227.96 +/- 33.07 mg/dl, p < 0.001), LDL-C (158.71 +/- 35.78 vs. 146.21 +/- 34.63 mg/dl, p < 0.01), TG (215.92 +/- 63.61 vs. 187.58 +/- 90 mg/dl, p < 0.05), ET-1 (2.44 +/- 0.51 vs. 1.74 +/- 0.42 pg/ml, p < 0.001) and membrane cholesterol (4.85 +/- 0.65 vs. 2.81 +/- 0.54 mmol/Lpc, p < 0.001), uric acid and fasting blood glucose levels did not change significantly after study cessation.. The results of our study show that anthocyanins from Aronia melanocarpa may be of benefit to patients with MS as for as atherosclerosis prevention is concerned. It seems to result from anthocyanins influence on blood pressure, serum lipid and endothelin-1 level.

Topics: Anthocyanins; Blood Glucose; Blood Pressure; Case-Control Studies; Cholesterol, HDL; Cholesterol, LDL; Endothelin-1; Female; Humans; Hyperinsulinism; Hypertension; Lipids; Lipoproteins; Male; Metabolic Syndrome; Middle Aged; Photinia; Plant Extracts; Triglycerides; Waist-Hip Ratio

This study was designed to investigate the effects of a sucrose diet on vascular and metabolic actions of insulin in spontaneously hypertensive rats (SHR). Male SHR were randomized to receive a sucrose or regular chow diet for 4 wk. Age-matched, chow-fed Wistar-Kyoto (WKY) rats were used as normotensive control. In a first series of experiments, the three groups of rats had pulsed Doppler flow probes and intravascular catheters implanted to determine blood pressure, heart rate, and blood flows. Insulin sensitivity was assessed during a euglycemic hyperinsulinemic clamp performed in conscious rats. In a second series of experiments, new groups of rats were used to examine glucose transport activity in isolated muscles and to determine endothelial nitric oxide synthase (eNOS) protein expression in muscles and endothelin content in vascular tissues. Sucrose feeding was shown to markedly enhance the pressor response to insulin and its hindquarter vasoconstrictor effect when compared with chow-fed SHR. A reduction in eNOS protein content in muscle, but no change in vascular endothelin-1 protein, was noted in sucrose-fed SHR when compared with WKY rats, but these changes were not different from those noted in chow-fed SHR. Similar reductions in insulin-stimulated glucose transport were observed in soleus muscles from both groups of SHR when compared with WKY rats. In extensor digitorum longus muscles, a significant reduction in insulin-stimulated glucose transport was only seen in sucrose-fed rats when compared with the other two groups. Environmental factors, that is, high intake of simple sugars, could possibly potentiate the genetic predisposition in SHR to endothelial dysfunction and insulin resistance.

Topics: Animals; Blotting, Western; Deoxyglucose; Dose-Response Relationship, Drug; Endothelin-1; Fructose; Glucose Clamp Technique; Hemodynamics; Hyperinsulinism; Hypertension; Hypoglycemic Agents; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Nitric Oxide Synthase Type III; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Regional Blood Flow; Sucrose

Low adipocyte IRS-1 protein expression is a biomarker for insulin resistance and early atherosclerosis. However, whether IRS-1 protein expression is related to systemic arterial stiffness, is unknown.. Ten non-diabetic male subjects with low adipocyte IRS-1 protein expression (LIRS) were matched with 10 non-diabetic males with normal IRS-1 protein expression (NIRS). Augmentation index (AIx) and time for reflection of pulse wave (Tr) were studied with pulse wave analysis, both in the fasting state and during a euglycemic hyperinsulinemic clamp. The LIRS-group showed an increased fasting insulin concentration (fP-insulin 71+/-4 pmol/L versus 58+/-5 pmol/L; p=0.02 (mean+/-S.E.)), whereas glucose disposal rate during the clamp (8.7+/-0.8 mg/kg LBM/min versus 10.3+/-1.3 mg/kg LBM/min; n.s.) did not differ significantly. Blood pressure, lipid parameters, adiponectin, endothelin-1 and CRP concentrations were similar. However, in the basal state, AIx was increased (129+/-4% versus 116+/-2%; p<0.02) and Tr was decreased (150+/-3 ms versus 171+/-5 ms; p<0.01), suggesting stiffer vessels in the LIRS-group. The LIRS-group exhibited an attenuated AIx response to hyperinsulinemia compared to the NIRS-group.. The data suggest that non-obese non-diabetic men with a low adipocyte IRS-1 protein expression have an increased systemic arterial stiffness.

Topics: Adipocytes; Adiponectin; Adult; Arteriosclerosis; Biomarkers; Blood Glucose; C-Reactive Protein; Diabetes Mellitus; Endothelin-1; Fasting; Female; Glucose Clamp Technique; Humans; Hyperinsulinism; Insulin Receptor Substrate Proteins; Insulin Resistance; Intercellular Signaling Peptides and Proteins; Male; Middle Aged; Phosphoproteins

We previously showed that chronic insulin infusion induces insulin resistance, hyperendothelinemia, and hypertension in rats (C. C. Juan, V. S. Fang, C. F. Kwok, J. C. Perng, Y. C. Chou, and L. T. Ho. Metabolism 48: 465-471, 1999). Endothelin-1 (ET-1), a potent vasoconstrictor, is suggested to play an important role in maintaining vascular tone and regulating blood pressure, and insulin increases ET-1 production in vivo and in vitro. In the present study, BQ-610, a selective endothelin A receptor antagonist, was used to examine the role of ET-1 in insulin-induced hypertension in rats. BQ-610 (0.7 mg/ml; 0.5 ml/kg body wt) or normal saline was given intraperitoneally two times daily for 25 days to groups of rats infused with either saline or insulin (2 U/day via sc-implanted osmotic pumps), and changes in plasma levels of insulin, glucose, and ET-1 and the systolic blood pressure were measured over the experimental period, whereas changes in insulin sensitivity were examined at the end of the experimental period. Plasma insulin and ET-1 levels were measured by RIA, plasma glucose levels using a glucose analyzer, systolic blood pressure by the tail-cuff method, and insulin sensitivity by an oral glucose tolerance test. Our studies showed that insulin infusion caused sustained hyperinsulinemia in both saline- and BQ-610-injected rats over the infusion period. After pump implantation (2 wk), the systolic blood pressure was significantly higher in insulin-infused rats than in saline-infused rats in the saline-injected group (133 +/- 3.1 vs. 113 +/- 1.1 mmHg, P < 0.05) but not in the BQ-610-injected group (117 +/- 1.2 vs. 117 +/- 1.8 mmHg). Plasma ET-1 levels in both sets of insulin-infused rats were higher than in saline-infused controls (2.5 +/- 0.6 and 2.5 +/- 0.8 vs. 1.8 +/- 0.4 and 1.7 +/- 0.3 pmol/l, P < 0.05). Oral glucose tolerance tests showed that BQ-610 treatment did not prevent the insulin resistance caused by chronic insulin infusion. No significant changes were found in insulin sensitivity and blood pressure in saline-infused rats treated with BQ-610. In a separate experiment, insulin infusion induced the increase in arterial ET-1 content, hypertension, and subsequent plasma ET-1 elevation in rats. These results suggest that, in the insulin infusion rat model, ET-1 plays a mediating role in the development of hypertension, but not of insulin resistance.

Topics: Animals; Blood Glucose; Disease Models, Animal; Drug Administration Schedule; Endothelin A Receptor Antagonists; Endothelin-1; Hyperinsulinism; Hypertension; Infusions, Intravenous; Insulin; Insulin Resistance; Male; Oligopeptides; Rats; Rats, Sprague-Dawley

Endothelial expression of cell adhesion molecules (CAMs) plays an important role in atherosclerosis. Atherosclerosis is increased in hyperinsulinemic states, but whether insulin per se is proatherogenic remains unclear. To investigate the effects of hyperinsulinemia on CAM expression, plasma levels of ICAM-1, VCAM-1 and E-selectin were measured before and after forearm infusion of insulin in healthy subjects. Insulin administration for 2h resulted in significant hyperinsulinemia, whereas no significant change was observed in soluble CAMs (all p > 0.05). Because insulin stimulates endothelial release of both endothelin-1 (ET-1) and nitric oxide (NO), which may modulate the expression of CAMs, we also investigated the response of CAMs to ET-1 receptor blockade, alone and in combination with NO synthesis inhibition. ET-1 receptor blockade during hyperinsulinemia resulted in a vasodilator response, but did not affect soluble CAMs (all p > 0.05). Superimposition of NO inhibition by L-NMMA reversed the vasodilator effect of ET-1 blockade, without affecting soluble CAMs (all p > 0.05). In conclusion, acute hyperinsulinemia, alone or during ET-1 and NO pathway blockade, does not affect soluble CAMs. These results do not support a direct effect of insulin on endothelial cells to affect leukocyte adhesiveness to the vascular wall.

Topics: Biomarkers; E-Selectin; Endothelin A Receptor Antagonists; Endothelin-1; Endothelium, Vascular; Enzyme Inhibitors; Forearm; Humans; Hyperinsulinism; Hypoglycemic Agents; Insulin; Intercellular Adhesion Molecule-1; Nitric Oxide; omega-N-Methylarginine; Reference Values; Regional Blood Flow; Vascular Cell Adhesion Molecule-1; Vasodilation

The aim of the study was to evaluate the relationship between exercise tolerance, glucose and insulin levels and biochemical parameters related to endothelial function [endothelin-1 (ET-1), nitrite/nitrate (NOx)] in patients with cardiological syndrome X in comparison with healthy volunteers. The decrease of NOx level and NOx / ET-1 ratio suggests that endothelial dysfunction is present in cardiological syndrome X. Exercise tolerance correlated positively with NOx and negatively with insulin concentrations.

Topics: Adult; Biomarkers; Blood Glucose; Case-Control Studies; Endothelin-1; Endothelium, Vascular; Exercise Tolerance; Female; Glucose Tolerance Test; Humans; Hyperinsulinism; Insulin; Male; Microvascular Angina; Middle Aged; Nitric Oxide

Insulin is not only a growth factor for vascular cells, but also an inducer of other vasoactive substances such as endothelin-1 (ET-1) in vascular cells. The aim of the present study was to assess the role of endothelial cells (EC) in insulin mediated vascular smooth muscle cell (VSMC) proliferation. Cultured human aortic EC and VSMC were separately incubated. EC were stimulated with insulin (0 to 1000 microU/mL) for 24 h, in the presence or absence of anti-insulin-growth factor-1 (anti-IGF-1) receptor antibody (alphaIR(3)) or a nonselective ET-1 receptor antagonist (TAK044). Cell proliferation was measured by determining (3)H-thymidine uptake. Although 10 microU/mL insulin did not affect ET-1 production in the EC culture medium, a higher concentration of insulin stimulated it. Production of ET-1 in EC was activated by insulin via the IGF-1 receptor, inasmuch as alphaIR(3) blocked insulin mediated upregulation of ET-1. There was no significant difference in (3)H-thymidine incorporation in the presence of insulin (up to 1000 microU/mL) or TAK044. Culture medium from EC stimulated with insulin enhanced VSMC proliferation, which was almost totally suppressed by TAK044. Insulin induced VSMC growth dose dependently when VSMC were cultured alone. In contrast, insulin at concentrations of 100 microU/mL or lower failed to stimulate growth of co-cultured VSMC, but only at 330 microU/mL or higher concentrations stimulated VSMC growth in this system. Of interest, VSMC proliferation was greatest when L-NAME was added and co-cultured with EC. In summary, a severely hyperinsulinemic state may regulate VSMC and EC proliferation via activation of vasoactive substances such as ET-1 and nitric oxide induced by insulin.

Topics: Aorta; Cell Division; Cells, Cultured; Coculture Techniques; Endothelin-1; Endothelium, Vascular; Humans; Hyperinsulinism; Hypoglycemic Agents; Insulin; Muscle, Smooth, Vascular; Nitric Oxide

In order to determine the effects of increasing insulin resistance on endothelin-1 (ET-1) levels, Zucker lean and fatty rats were studied at basal and during a complete nutrient meal tolerance test (MTT) at 7, 12, and 15 weeks of age. The fatty rats were mildly hyperglycemic, severely hyperinsulinemic and glucose-intolerant at all ages versus lean animals and this progressed with age within groups, as previously published. Basal ET-1 levels, at 7 weeks, were significantly increased in fatty versus lean rats (3.2+/-0.5 v 2.0+/-0.3 pg/mL, respectively; P<.05); however, we did not observe any significant basal difference at 12 or 15 weeks. At 7 weeks, ET-1 levels between fatty and lean rats were not different during the MTT (15 minutes: 2.9+/-0.4 v 2.7+/-0.7; 120 minutes: 6.5+/-0.8 v 6.6+/-0.5 pg/mL, fatty v lean, respectively). At 12 weeks, though there was no difference in basal levels, fatty rats had higher ET-1 levels during the MTT compared to lean animals (15 minutes: 6.9+/-1.4 v 1.8+/-0.4; 120 minutes: 9.4+/-1.7 v 3.2+/-0.5 pg/mL, respectively; P<.01). At 15 weeks, ET-1 levels during the MTT receded to levels similar to those observed at 7 weeks, which were significantly higher in fatty versus lean rats 15 minutes following the challenge (3.4+/-0.4 v 2.4+/-0.2 pg/mL, respectively; P<.05). In conclusion, ET-1 levels in the Zucker fatty rat: (1) were increased in the early stages of the progression of insulin resistance at 7 weeks, but were unchanged under basal conditions with age thereafter, and (2) were increased under nutrient challenge conditions with advanced insulin resistance up to 12 weeks, and were still significantly but to a lesser degree increased at 15 weeks of age. The explanation for these results and their relationship to the observed insulin resistance is unclear and will require further investigation.

Topics: Aging; Animals; Blood Glucose; Endothelin-1; Fasting; Food; Glucose Intolerance; Hyperglycemia; Hyperinsulinism; Insulin; Insulin Resistance; Obesity; Rats; Rats, Zucker

Hyperinsulinemia, a primary feature of insulin resistance, is associated with increased endothelin-1 (ET-1) activity. This study determined the vascular response to ET-1 and receptor binding characteristics in small mesenteric arteries of insulin-resistant (IR) rats. Rats were randomized to control (C) (n = 32) or IR (n = 32) groups. The response to ET-1 was assessed (in vitro) in arteries with (Endo+) and without (Endo-) endothelium. In addition, arteries (Endo+) were pretreated with the ET(B) antagonist A-192621 or the ET(A) antagonist A-127722. Finally, binding characteristics of [(125)I]ET-1 were determined. Results showed that in Endo+ arteries the maximal relaxation (E(max)) to ET-1 was similar between C and IR groups; however, the concentration at 50% of maximum relaxation (EC(50)) was decreased in IR arteries. In Endo- arteries, the E(max) to ET-1 was enhanced in both groups. Pretreatment with A-192621 enhanced the E(max) and EC(50) to ET-1 in both groups. In contrast, A-127722 inhibited the ET-1 response in all arteries in a concentration-dependent manner; however, a greater ET-1 response was seen at each concentration in IR arteries. Maximal binding of [(125)I]ET-1 was increased in IR versus C arteries although the dissociation constant values were similar. In conclusion, we found the vasoconstrictor response to ET-1 is enhanced in IR arteries due to an enhanced expression of ET receptors and underlying endothelial dysfunction.

Topics: Animals; Body Weight; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelin-1; Hyperinsulinism; In Vitro Techniques; Insulin Resistance; Iodine Radioisotopes; Male; Mesenteric Arteries; Muscle, Smooth, Vascular; Pyrrolidines; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin

There is growing evidence that hypertriglyceridemia exacerbates ischemic injury. We tested the hypothesis that triglycerides impair myocardial recovery from low-flow ischemia in an ex vivo model and that such an effect is related to endothelin-1. Hyperglycemic (glucose concentration = 12 mmol/l) and hyperinsulinemic (insulin concentration = 1.2 micromol/l) isolated rat hearts were perfused with Krebs-Henseleit buffer (PO(2) = 670 mmHg, pH 7.4, 37 degrees C) added with increasing triglycerides (0, 1,000, 2,000, and 4,000 mg/dl, n = 6-9 rats/group). Hearts were exposed to 60 min of low-flow ischemia (10% of basal coronary flow), followed by 30 min of reperfusion. We found that increasing triglycerides impaired both the diastolic (P < 0.005) and systolic (P < 0.02) recovery. The release of endothelin-1 during reperfusion increased linearly with triglyceride concentration (P = 0.0009). Elevated triglycerides also increased the release of nitrite and nitrate (NO(x)), the end products of nitric oxide, up to 6 micromol/min. Trimetazidine (1 micromol) further increased NO(x) release, blunted endothelin-1 release, and protected myocardial function during recovery. We conclude that high triglyceride levels impair myocardial recovery after low-flow ischemia in association with endothelin-1 release. The endothelium-mediated effect of triglycerides on both contractile recovery and endothelin-1 release is prevented by 1 microM trimetazidine.

Topics: Animals; Dose-Response Relationship, Drug; Endothelin-1; Glucose; Heart Rate; Hyperglycemia; Hyperinsulinism; In Vitro Techniques; Insulin; Male; Myocardial Ischemia; Myocardial Reperfusion; Oxygen Consumption; Rats; Rats, Sprague-Dawley; Recovery of Function; Reperfusion Injury; Triglycerides; Trimetazidine; Vasodilator Agents; Ventricular Function, Left

The effect of contractions elicited with ET1 and AVP after preincubating rat aortic and tail artery rings with a hyperinsulinemic dose (3 nM) of insulin were studied. Insulin preincubation (120 min), in the presence of 0.1 mM L-NAME, depressed contraction of aortic rings to 0.01 microM ET1 (132 +/- 6 vs. 161 +/- 9 mg/mm2 in control, n = 25; p < 0.05) and to 1 microM AVP (84 +/- 7 vs. 110 +/- 9 mg/mm2 in control, n = 16; p < 0.05), but did not modify 45Ca influx to the cell. Insulin-induced relaxation was inhibited by indomethacin 10 microM, an antagonist of prostaglandin synthesis, and also by blockade of insulin receptors with 30 microM genistein. A short insulin preincubation (15 min) did not modify ET1 contractions. In rat tail artery, insulin preincubation (120 min) increased the force developed by ET1 (847 +/- 45 vs. 596 +/- 99 mgF/mgW in controls, n = 14) by stimulating TXA2 release and/or actions. In summary, the present results suggest that endothelial factors are involved in both the vasoconstrictor and vasodilator effects of insulin on rat vessels.

Topics: Animals; Aorta; Arginine Vasopressin; Drug Interactions; Endothelin-1; Endothelium, Vascular; Enzyme Inhibitors; Hyperinsulinism; Insulin; Male; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Prostaglandin-Endoperoxide Synthases; Protein-Tyrosine Kinases; Rats; Rats, Wistar; Receptors, Thromboxane; Tail; Vasoconstriction

In the present work, we studied the possible mechanisms involved in the insulin-induced acceleration of ET1 contractions. We observed a shortening of the half-life needed to achieve maximal developed force (t(1/2)) at 10(-7) M ET1 in rat aortic rings preincubated for 120 min with 3 nM insulin (control 380 +/- 15 s vs. 319 +/- 8 s with insulin, n = 28, p < 0.05). A tyrosine kinase linked receptor was involved in this effect because it was abolished by 30 microM genistein. Endothelium denudation and 10 microM indomethacin treatment did not effect this insulin effect, suggesting its independence of endothelial-derived factors. The effect was still present when the only source of Ca2+ was intracellular (t(1/2) values in the absence of external Ca2+: control 467 +/- 68 s vs. 213 +/- 28 s with insulin, n = 16, p < 0.05), but was blunted if the sarcoplasmic reticulum (SR) Ca2+ source was suppressed by exposure to 10 microM thapsigargin or 10 microM ryanodine. Preincubation with insulin did not potentiate either SR 45Ca2+ uptake or contractions evoked by caffeine-sensitive SR Ca2+ release. Since 30 microM cheleritrine abolished insulin-induced acceleration of ET1 contractions, we propose that the hormone might enhance a signal pathway related to PKC in order to produce a faster Ca2+ release from the SR.

Topics: Animals; Aorta; Caffeine; Calcium; Endothelin-1; Endothelium, Vascular; Enzyme Inhibitors; Hyperinsulinism; Insulin; Male; Protein Kinase C; Rats; Rats, Wistar; Sarcoplasmic Reticulum; Vasoconstriction

Earlier, we reported that high insulin incubation in vitro leads to increased ETA receptor expression in cultured rat aortic smooth muscle cells (Diabetes 1998, 47: 934-944). Our later observation of enhanced endothelin-1 evoked vasoconstriction in aorta from the hyperinsulinemic obese Zucker rat indicated that this interaction might also be relevant in vivo. To further examine the relationship between insulinemia and endothelin, we characterized endothelin receptor expression and endothelin-1 peptide levels in vascular tissues and plasma from young and old obese Zucker rats.. 12 and 40-week-old Zucker obese and lean rats were used. Plasma endothelin-1 levels and endothelin-1 peptide content in the mesenteric artery and in the thoracic aorta were examined by radioimmunoassay. Messenger RNA levels of endothelin-1 peptide and ETA and ETB receptors were examined in the aortic and mesenteric vessels using RT-PCR.. Obese rats from both age groups had significantly higher plasma levels of insulin (4-10 fold), total cholesterol (2-3 fold), triglycerides (10-fold), and glucose (approximately 1.5 fold) than their lean counterparts. There was a trend toward worsening lipoproteinemia and glycemia, but improved insulinemia with age in the obese rats. In association with these changes, obese rats exhibited attenuated endothelin-1 peptide and preproET-1 mRNA levels, but conversely elevated ETA and ETB receptor mRNA levels in both aortic and mesenteric vessels.. These data suggest that vascular tissue from the metabolically dysregulated obese Zucker rat exhibits attenuated endothelin-1 peptide production and elevated endothelin receptor levels. Since elevated insulin levels have been linked to increased endothelin receptor expression, it is plausible that hyperinsulinemia upregulates endothelin receptors contributing to elevated vasoconstrictor responses to endothelin-1 in this model of obesity and hypertension.

Topics: Animals; Aorta, Thoracic; Blotting, Southern; Endothelin-1; Hyperinsulinism; Insulin Resistance; Male; Mesenteric Arteries; Obesity; Paracrine Communication; Rats; Rats, Zucker; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

In many clinical and animal studies, hypertension and insulin resistance coexist, but their mechanistic relationship is unclear. We explored the causal link between these two parameters in a rat model with chronic hyperinsulinemia induced with human insulin (1 U/d) released from subcutaneously implanted minipumps. Rats with saline minipumps served as a control. During the first experiment, plasma levels of insulin and glucose and the systolic blood pressure of the two groups were continuously monitored for 17 days. In the subsequent four experiments, rats were killed on days 10 and 13 to measure plasma endothelin-1 (ET-1) levels and the glucose transport into and insulin and ET-1 binding of isolated adipocytes. In one experiment, rats were tested for oral glucose tolerance on days 10 and 13. In another experiment, ET-1 binding to the aortic plasma membrane was also determined. The results showed that rats became hyperinsulinemic throughout the experimental period by the instillation of exogenous insulin. Hyperinsulinemic rats were consistently hypoglycemic during the first day, but they became euglycemic thereafter, indicating an insulin-resistant state. Glucose intolerance was obvious by day 10, but significant hypertension was not detected until the 11th day on insulin infusion. Compared with the saline controls, insulin-infused rats had an increase of plasma ET-1 levels but a decrease of both basal and insulin-stimulated glucose transport into adipocytes. ET-1 binding to adipocytes of the insulin-infused group was elevated significantly from day 10 through day 13. ET-1 binding to the aortic membranes, supposedly downregulated by the increased plasma ET-1 and hypertension, was similar to that found in the controls on day 13. These results imply that hyperinsulinemia in rats could lead to hypertension via the elevation of plasma ET-1 levels together with an unaltered vascular binding of ET-1, which was probably unrelated to the insulin resistance.

Topics: Adipocytes; Animals; Blood Glucose; Blood Pressure; Cell Membrane; Endothelin-1; Endothelium, Vascular; Glucose Tolerance Test; Hyperinsulinism; Hypertension; Hypoglycemic Agents; Insulin; Insulin Infusion Systems; Insulin Resistance; Male; Rats; Rats, Sprague-Dawley

Insulin stimulates the production of endothelin-1 (ET-1) and nitric oxide (NO) by isolated endothelial cells. Additionally, insulin-dependent glucose transport and insulin-mediated NO production partially share common elements in signal transduction. There are discordant data on plasma ET-1 levels during acute euglycemic systemic hyperinsulinemia in normotensive men and men with essential hypertension (EH) (known to be insulin-resistant), as well as on the relations between insulin sensitivity and vascular function. Our aim was to assess the response of approximate measures of whole-body generation of NO and ET-1 to acute euglycemic hyperinsulinemia in EH patients and controls. We studied 17 newly diagnosed untreated men with uncomplicated EH and 10 normotensive controls. Plasma ET-1 and urinary excretion of nitrite plus nitrate, stable NO metabolites (Uno(x)), were measured before and during a 3-hour hyperinsulinemic-euglycemic clamp. Both in hypertensives and normotensives, plasma ET-1 levels were reduced after 2 hours of the clamp (EH: baseline, 3.1+/-1.9 pg/mL; 2 hours, 1.9+/-1.2 pg/mL, P = .04 v baseline; controls: baseline, 4.2+/-2.6 pg/mL; 2 hours, 2.8+/-1.4 pg/mL, P = .04 v baseline). No significant changes in Uno(x) during the clamp were observed. Changes in Uno(x) during the clamp (deltaUno(x)) and differences in plasma ET-1 measured before the end and before the beginning of the clamp (deltaET-1) were correlated in the controls (r = .75, P = .01) but not in EH (r = -.01, P = .97). No parameter of glucose metabolism correlated with basal Uno(x), basal plasma ET-1, deltaUno(x), and deltaET-1, whether absolute or percent values, in either group. Thus, acute euglycemic hyperinsulinemia produces a decrease in plasma ET-1 in both EH patients and controls. The lack of correlation between deltaUno(x) and deltaET-1 under these conditions in EH may suggest an impairment of systems governing interactions between the NO-dependent pathway and ET-1. In addition, insulin actions on glucose metabolism and on the endothelial mediators appear dissociated.

Topics: Acute Disease; Adult; Blood Glucose; Endothelin-1; Humans; Hyperinsulinism; Hypertension; Male; Middle Aged; Nitrates; Nitrites; Reference Values

We evaluated venous plasma ET-1 concentrations in 18 never-treated obese men (body mass index 31.0 +/- 0.5 kg/m2; age 45.4 +/- 4.3 years) showing the whole features of the above syndrome and 12 control men (age 44.1 +/- 3.6 years). Circulating ET-1 levels were significantly higher in patients than in controls (p < 0.05), and were directly correlated with fasting insulin levels (r = 0.564, p = 0.015) and erythrocyte Na+/Li+ counter-transport activity (r = 0.504, p = 0.033). In conclusion, venous plasma ET-1 levels are elevated in obese men manifesting the whole features of the metabolic syndrome. Due to the biological properties of ET-1, our findings suggest the peptide as a further component of the cluster of cardiovascular risk factors which characterizes this syndrome.

Topics: Adult; Blood Glucose; Blood Urea Nitrogen; Cholesterol; Diastole; Endothelin-1; Heart Rate; Humans; Hyperinsulinism; Insulin; Insulin Resistance; Lipoproteins; Male; Middle Aged; Obesity; Reference Values; Regression Analysis; Syndrome; Systole

Elevations in circulating levels of both endothelin-1 (ET-1) and insulin are found in coronary heart disease and chronic heart failure. Although several studies have shown that insulin can stimulate ET-1 release from endothelial cell cultures, in vivo studies have yielded equivocal results. We sought to determine whether endogenous insulin at physiological concentrations leads to alterations in venous plasma ET-1 levels in healthy subjects. In addition, we investigated the effects of physiological and supraphysiological doses of insulin on the release of ET-1 from human umbilical vein endothelial cells (HUVECs) in vitro. In the in vitro experiment, ET-1 and insulin levels were measured during an intravenous glucose tolerance test (IVGTT) in 10 healthy subjects. In the in vitro experiment, HUVECs were incubated in the absence of serum and with different concentrations of insulin (25 pmol/L to 1 mumol/L) for 4 hours before measurement of secreted ET-1. The in vivo study showed no significant alterations in venous plasma ET-1 levels during IVGTTs (maximum plasma insulin, 616.9 +/- 147.0 pmol/L [mean +/- SEM]). In the in vitro experiment, increases in ET-1 release were observed under serum-free conditions at 100 pmol/L (physiological) and 1 mumol/L (supraphysiological) insulin (ET-1, 22.4% and 46.4% higher than control cultures, respectively, both P < .05). Our results show that insulin at physiological concentrations does not alter plasma ET-1 levels in healthy individuals, but does stimulate its secretion from vascular endothelial cells in vitro. This may have implications for the study of elevated ET-1 in hyperinsulinemic states.

Topics: Blood Glucose; Cells, Cultured; Dietary Carbohydrates; Endothelin-1; Endothelium, Vascular; Fasting; Female; Glucose Tolerance Test; Humans; Hyperinsulinism; Insulin; Male; Umbilical Veins

Acute hyperinsulinemia does not increase circulating ET-1 levels in subjects with normal and deranged glucose metabolism.

Topics: Adolescent; Adult; Aged; Diabetes Mellitus, Type 2; Endothelin-1; Female; Glucose Clamp Technique; Humans; Hyperinsulinism; Hypoglycemic Agents; Infusions, Intravenous; Insulin; Male; Middle Aged