Reactivity of Mesenteric Arteries From Fructose Hypertensive Rats to Endothelin-1

We previously demonstrated that mesenteric arteries from hyperinsulinemic, insulin resistant fructose hypertensive (FH) rats contain a higher absolute amount of ET-1 and exhibit defective endothelium-dependent vasodilation. Furthermore, chronic ET receptor blockade with bosentan completely prevented the rise in blood pressure in these rats. The present study was undertaken to examine 1) whether the reactivity of mesenteric arteries to ET-1 is altered in FH rats, and 2) whether chronic bosentan treatment has any effect on ET-1 responsiveness and endothelium-dependent vasodilation. Male Sprague Dawley rats were divided into four groups: control (C), control bosentan-treated (CB), fructose (F) and fructose bosentan-treated (FB). Chronic oral bosentan treatment (100 mg/kg/day) was initiated in the CB and FB groups 1 week prior to initiating the fructose diet. At week 16, the F group was hyperinsulinemic and hypertensive when compared to the C group (plasma insulin: 5.8 ± 0.3 v C 3.2 ± 0.5 ng/mL, P < .001; systolic BP: 157 ± 5 v C 130 ± 4 mm Hg, P < .001). Treatment of the F group with bosentan prevented the rise in BP (FB: 133 ± 3 mm Hg; P < .001 v F). Analysis of the pressurized mesenteric resistance arterioles demonstrated that the wall thickness as expressed as percentage of internal diameter did not differ between arteries from C and F rats, when measured over a range of transmural pressures. Constrictor responses of resistance arterioles to NE were similar for C and F rats when studied at transmural pressures of either 120 mm Hg or 160 mm Hg, respectively. The maximum contractile response and the sensitivity of superior mesenteric arteries to NE did not differ between the groups, either with or without the endothelium. However, the maximum contractile response to ET-1 was depressed in the F group both with (+) and without (−) the endothelium [(+): 1.50 ± 0.11 v C 1.88 ± 0.1 g/mm³, P < .05, (−): 1.68 ± 0.11 v C 2.05 ± 0.1 g/mm³, P < .05.]. Furthermore, the endothelium intact F arteries exhibited a decreased sensitivity to ET-1 (pD₂ values F 8.36 ± 0.11 v C 8.83 ± 0.07). Chronic bosentan treatment of the F group restored the maximum tension responses of arteries to ET-1 [(+) in the FB group: 1.88 ± 0.12 g/mm³ v C, P > .05, (−): 1.95 ± 0.05 g/mm³ v C, P > .05] but had no effect on the responses of the CB group. In arteries with intact endothelium, bosentan treatment restored the sensitivity of the F arteries to ET-1 (pD₂ values FB 8.82 ± 0.05 v C, P < .05). Endothelium-dependent relaxation responses were diminished in the F group, which were unaffected by bosentan treatment. These data suggest that mesenteric arteries from FH demonstrate a specific alteration towards the reactivity to ET-1, which is restored by long-term bosentan treatment.     

A high sucrose,high linoleic acid diet potentiates hypertension in the dahl salt sensitive rat

Insulin resistance can be induced by diets high in simple carbohydrates or fatty acids. To determine whether these nutrients also affect arterial pressure in genetic models of salt sensitive and salt resistant hypertension, Dahl salt sensitive (S) and salt resistant (R) rats were each fed the following isocaloric diets containing 3% NaCl for 4 weeks (10 rats/group): 1) control; 2) high sucrose (60%); 3) high linoleic acid (LA, provided as 10% safflower oil); and 4) high sucrose plus high LA. Tail systolic blood pressures (SBP) were measured weekly, and at 4 weeks, direct mean arterial pressures (MBP) were measured in conscious animals. Insulin sensitivity was assessed by in vitro uptake of tritiated glucose by adipocytes in response to graded doses of insulin.Weight gain did not differ among groups. High sucrose alone and high LA alone did not affect blood pressure in either strain. However, SBP and MBP were increased (P < .05) by the high sucrose plus high LA diet in Dahl-S but not in Dahl-R rats. Sucrose alone and LA alone decreased (P < .05) insulin sensitivity in Dahl-S and Dahl-R rats. In both strains, sucrose plus LA decreased insulin sensitivity to a greater extent (P < .05) than sucrose alone or LA alone.Thus, the sucrose plus LA diet decreased insulin sensitivity in both Dahl-S and Dahl-R rats, whereas blood pressure was increased only in Dahl-S rats. The phenotype of elevated arterial pressure is influenced both by a genetic-nutrient interaction and by an interaction among specific nutrients resulting in insulin resistance.     

High Plasma Immunoreactive Leptin Level in Essential Hypertension

Insulin resistance, the most important factor in metabolic syndrome X, has been considered to raise blood pressure. Recently it was reported that insulin resistance was related to an elevated plasma level of leptin, which is an adipocyte-specific ob gene product and which plays a role in food intake suppression, thermogenesis, and energy expenditure through the activation of the hypothalamus. However there are no reports that deal with the relationship of insulin resistance to plasma leptin and blood pressure.To evaluate the role of leptin in essential hypertensives, two groups of subjects who were carefully matched for body mass index (BMI) were studied; 22 normotensives (NT, age: 46.5 ± 2.6 years, BMI: 23.9 ± 0.4 kg/m², male/female: 14/8) and 45 mild-to-moderate essential hypertensives (EHT, age: 51.9 ± 2.0 years, BMI: 24.5 ± 0.4 kg/m², male/female: 21/24). We applied the euglycemic hyperinsulinemic glucose clamp technique to all subjects and insulin sensitivity was evaluated as the M value. EHT showed a significantly lower M value (160.2 ± 7.4 v 184.3 ± 7.3 mg/m²/min, P < .05) and higher basal plasma immunoreactive leptin level (7.6 ± 0.8 v 5.0 ± 0.8 ng/mL, P < .05) than NT, despite the fact that there was no significant difference between NT and EHT in age, gender, or BMI. The relationship between mean blood pressure and leptin showed a significant positive correlation in all of the subjects (r = 0.31, P < .05), suggesting that leptin may be related to a pathophysiology of essential hypertension.     

Renal Depressor Mechanisms of Physical Training in Patients With Essential Hypertension

To clarify characteristics of the patients in whom exercise training lowers blood pressure and to elucidate the mechanisms by which exercise training lowers blood pressure, we evaluated 24-h blood pressure, glomerular filtration rate (GFR), renal blood flow (RBF), filtration fraction (FF), plasma renin activity (PRA), plasma aldosterone concentration (PAC), plasma norepinephrine concentration (PNE), and incremental area of insulin/glucose (ΣI/ΣG) during 75 g oral glucose tolerance test, and assessed arterial baroreceptor function (BSI) before and after a 3-week exercise training program (four 6-min sessions daily at 75% V̇O₂ max). Patients were classified as responders (n = 15) if they showed statistically significant reduction in the multiple comparison of 24-h mean arterial pressure (MAP), or as nonresponders (n = 15) if they did not. Although there were no significant differences between responders and nonresponders in age, weight, MAP, GFR, RBF, RPF, FF, PNE, ΣI/ΣG, or BSI before exercise, renal vascular resistance (RVR; P < .05), PRA (P < .05), and PAC (P < .05) were significantly higher in responders than in nonresponders. The fractional excretion of sodium (FENa) (P < .05) were significantly lower in responders than in nonresponders. After exercise training, FF (P < .01), RVR (P < .05), PNE (P < .05) PRA (P < .01), and ΣI/ΣG (P < .05) decreased significantly only in responders. The decrease in MAP significantly correlated with the reductions in FF (r = 0.46, P < .05), PNE (r = 0.52, P < .01) and RVR (r = 0.40, P < .05). Thus, in patients who have higher RVR and PRA, exercise training lowered blood pressure in parallel to a reduction in RVR associated with decreases in sympathetic tone and improvement of insulin resistance. Our results suggest that exercise-induced changes in renal hemodynamics may contribute to the reduction in blood pressure in these patients.     

Low dietary magnesium is associated with insulin resistance in a sample of young,nondiabetic black Americans

In both humans and experimental animals, dietary induced magnesium deficiency is correlated with insulin resistance. The purpose of this study was to determine whether dietary magnesium intake is associated with insulin sensitivity or blood pressure in a sample of nondiabetic, young adult black Americans. We also examined dietary calcium, potassium, and sodium intake. The study was conducted on a sample (n = 179) of young adults aged 30 ± 3.4 years who had been followed longitudinally. Nutrient intake was assessed by obtaining a 24-h recall interview of dietary intake. Intake data were entered in a nutrient analysis program (Nutritionist III), which quantitated micronutrients, macronutrients, and minerals. We classified the sample into insulin-sensitive (IS) and insulin-resistant (IR) groups, according to insulin-stimulated glucose use (M) measured during insulin clamp. M correlated positively with magnesium intake in mg/kg of fat-free mass (r = 0.15, P < .05 overall; in men, r = 0.25, P < .02). There was a significant negative correlation of total dietary magnesium intake with the sum of insulin levels measured during an oral glucose tolerance test (OGTT) (r = −0.13, P < .05). When corrected for body fat, in men there was also a significant correlation of dietary magnesium intake, measured in mg/kg of fat-free mass, with the sum of insulin concentrations on the OGTT (r = −0.22, P < .05). When cases were categorically classified as IS versus IR, magnesium intake in mg/kg of fat-free mass was lower in IR (2.97 ± 1.4) than in IS (3.68 ± 2.2; P = .022). These results suggest a possible role for dietary magnesium in insulin resistance.     

Endothelin-1 released by vascular smooth muscle cells enhances vascular responsiveness of rat mesenteric arterial bed exposed to high perfusion flow

Vasodilation of resistance vessels ensues in response to increased perfusion flow to maintain tissue perfusion. The flow-induced vasodilation is mainly dependent on nitric oxide (NO), which also regulates vascular responsiveness to vasoconstrictors. Besides NO, however, high flow increases endothelin-1 (ET-1) production from endothelial cells. It is likely, therefore, that the interaction between NO and ET-1 may play a critical role in the control of arterial vascular tone under high perfusion flow.In this study, the vascular responsiveness (VR) to high flow rate and the role of ET-1 released by vascular smooth muscle cells (VSMC) were evaluated in isolated and in vitro-perfused mesenteric arteries (MA). MA were perfused at constant (3.5 mL/min; CPF) and increased flow rate (4.5, 5.5, 6.5 mL/min; IPF). VR was evaluated by infusing norepinephrine (NE; 5 μmol/L) and potassium chloride (KCl; 80 mmol/L). Mesenteric vascular resistance (MVR), ET-1, and cGMP release were measured under different flow rates. The role of endothelium-derived ET-1 was evaluated by perfusing MA with phosphoramidon (endothelin converting enzyme inhibitor), whereas the role of other endothelium-derived vasoactive substances was excluded by measuring VR in MA without endothelium. Finally, ETA and ETB receptor antagonists were perfused in disendothelized MA. In the IPF group of intact MA, MVR dropped (P < .05) and both ET-1 and cGMP increased in the perfusate (P < .05). VR was enhanced by high flow after NE (101 ± 9 v 56 ± 12 mm Hg in CPF, P < .005) and KCl (119 ± 12 v 51 ± 10 mm Hg in CPF, P < .005) and it was unaffected by either phosphoramidon or endothelium removal. On the contrary, BQ-610 abolished the flow-dependent increase in VR. No further additive effect was achieved with BQ-788. In conclusion, in MA, high flow reduces MVR and concurrently enhances VR, likely through VSMC-derived ET-1.     

Effect of pioglitazone on insulin sensitivity,vascular function and cardiovascular inflammatory markers in insulin‐resistant non‐diabetic Asian Indians

Aims To determine the effects of pioglitazone (30 mg once daily for 16 weeks) on insulin sensitivity, insulin‐mediated vasodilation, vascular inflammatory markers, fat distribution and lipids in Asian Indians and Caucasians of European ancestry. Methods Cross‐sectional study. Eighteen non‐diabetic Asian Indians and 17 Caucasians of comparable age (34 ± 3 vs. 36 ± 3 years) and body mass index (26.0 ± 1.2 vs. 24.7 ± 1.0 kg/m²) had measurements of insulin sensitivity (M, insulin clamp at 6 pmol/kg per min), abdominal fat (computed tomographic scan at L4‐L5), endothelial‐dependent (reactive hyperaemia, RH) and ‐independent (0.4 mg sublingual nitroglycerin, TNG) vasodilation using brachial artery ultrasound before and after the 2‐h clamp at baseline and after pioglitazone therapy. Results Asian Indians were insulin resistant compared with Causasians during the baseline clamp (M = 25.6 ± 1.7 vs. 41.1 ± 2.2 µmol/kg per min, P < 0.0001) and improved significantly after pioglitazone (to 33.9 ± 1.7 µmol/kg per min, P < 0.001). Vasodilatory responses to RH and TNG were similar in Asian Indians and Caucasians at baseline and did not change. Insulin‐mediated vasodilation improved after pioglitazone in Asian Indians, but not in Caucasians, and correlated with the change in insulin sensitivity (r = 0.52, P = 0.03). C‐reactive protein (CRP) was higher in Asian Indians vs. Caucasians (1.6 ± 0.4 vs. 0.9 ± 0.2 mg/l) and was negatively correlated with insulin sensitivity (r = ?0.53, P = 0.02). In the Asian Indian group, CRP and plasminogen activator inhibitor‐1 decreased and adiponectin increased after pioglitazone, but there were no significant changes in total or visceral fat. Conclusions These results demonstrate that insulin‐resistant Asian Indians respond favourably to an insulin sensitizer with improvements in insulin sensitivity, cardiovascular and inflammatory risk markers, and vascular responses to insulin. These agents may have a role in decreasing the risk of diabetes and cardiovascular disease in this high‐risk population.     

Pioglitazone attenuates basal and postprandial insulin concentrations and blood pressure in the spontaneously hypertensive rat

Subjects with hypertension are hyperinsulinemic and resistant to insulin-stimulated glucose uptake. A similar paradigm is found in the spontaneously hypertensive rat (SHR). These findings suggest the possibility that insulin resistance and hyperinsulinemia may play an important role in blood pressure regulation. Pioglitazone, a thiazolidinedione derivative, sensitizes target tissues to insulin and decreases hyperglycemia and hyperinsulinemia in various insulin-resistant animals. The purpose of this study was to assess the influence of pioglitazone administration on pre- and postprandial glucose and insulin concentrations and determine whether changes in β-cell secretion resulted in any change in blood pressure measurements. Twelve SHR were fed custom diets ad libitum, six with and six without pioglitazone (20 mg/kg chow). Fasting and postprandial glucose levels were unaltered by pioglitazone treatment. Fasting insulin concentrations were similar at week 1, but were significantly lower (P < .01) in the pioglitazone group at weeks 3 (1.89 ± 0.3 v7.94 ± 1.5 ng/mL) and 4 (4.5 ± 1.4 v9.1 ± 0.7 ng/mL), compared with the control group. Pioglitazone also significantly (P < .01) lowered postprandial insulin concentrations after an oral glucose challenge. Systolic, mean, and diastolic blood pressures were significantly lower (P < .01), 177 ± 3 v190 ± 4.7 mm Hg, 162 ± 2.1 v175 ± 5.9 mm Hg, and 156 ± 2.1 v168 ± 6.2 mm Hg, respectively, in the animals receiving pioglitazone versus the control group. Heart rate, body weight, serum cholesterol, and triglyceride levels were comparable between the two groups. In conclusion, pioglitazone significantly decreased fasting and postprandial insulin concentrations and effectively lowered blood pressure in the SHR.     

Impairment of Endothelial Function in Salt-Sensitive Hypertension in Humans

In this study, we evaluated the relationship between the endothelium-dependent vasodilation and salt sensitivity in patients with essential hypertension. Fifteen untreated hypertensive male patients (age, 29 to 54 years) were sodium restricted (5 g/day) for 1 week, and placed on a high salt diet (20 g/day) the second week. At the end of each period, measurements of forearm vascular responses to drugs (acetylcholine, 3 to 24 μg/min; sodium nitroprusside, 0.15 to 1.2 μg/min; norepinephrine, 0.15 to 1.2 μg/min; and N^G-monomethyl-l-arginine [L-NMMA], 1 to 8 μmol/min) were obtained by using strain-gauge venous plethysmography. Subjects were divided into two groups according to the blood pressure response to sodium loading: salt-sensitive hypertensive group (24-h mean increase of arterial pressure ≥10%; n = 6) and salt-resistant group (<10%; n = 9). The two groups showed no significant difference in clinical data or mean arterial pressure during low salt intake. The dose-dependent vasodilation induced by acetylcholine was significantly reduced (P < .05) in the salt-sensitive hypertensive patients v the salt-resistant patients regardless of sodium loading. There were no differences between the two groups in response to sodium nitroprusside, norepinephrine, or L-NMMA. These results indicate that vasodilation to acetylcholine is reduced in salt-sensitive hypertensive patients even on restricted sodium diets. This may contribute to blood pressure elevation when sodium intake is increased.     

Erythropoietin impairs endothelium-dependent vasorelaxation through cyclooxygenase-dependent mechanisms in humans

Hypertension is a major complication of recombinant human erythropoietin therapy in patients with end-stage renal disease. Although the mechanisms for this pressor effect remain unknown, in vitro and ex vivo experiments suggest that erythropoietin stimulates release of cyclooxygenase-dependent endothelium-derived contracting factors (EDCFs) and attenuates endothelium-dependent vasorelaxation. To investigate the effect of erythropoietin on human endothelial function, we measured forearm blood flow by strain gauge plethysmography before and after intraarterial incremental administration of erythropoietin (10 to 300 IU/min, total 3000 U), while infusing acetylcholine (4 to 24 μg/min) and sodium nitroprusside (0.2 to 1.2 μg/min) in healthy male volunteers (n = 12). To examine a possible role of EDCFs, we repeated the same protocol under the pretreatment with oral indomethacin (50 mg), a cyclooxygenase inhibitor (n = 8). Infusion of erythropoietin into the brachial artery increased the erythropoietin blood concentration of venous effluents significantly (P < .0001) without changes in blood pressure and basal forearm blood flow. Acetylcholine and sodium nitroprusside increased forearm blood flow dose dependently before and after erythropoietin administration. However, acetylcholine-induced vasodilation (endothelium dependent) was significantly attenuated (P < .001) after erythropoietin administration, whereas vasodilation to sodium nitroprusside (endothelium independent) was unchanged. After indomethacin pretreatment, erythropoietin no longer attenuated endothelium-dependent vasorelaxation. Our results indicate that erythropoietin may impair endothelial function acutely, probably through cyclooxygenase-dependent EDCFs in humans. Long-term effects of erythropoietin on endothelial function in uremic patients remain to be elucidated.     

Reduction of Capillary Permeability in the Fructose-Induced Hypertensive Rat

Impaired insulin transcapillary transport and the subsequent decrease in insulin delivery to target organs have been suggested to play a role in insulin resistance. These defects were studied in fructose-fed rats, an animal model with insulin resistance. For this study, male Sprague-Dawley rats were fed with either a 60% fructose enriched (F) or a standard chow diet (N) for a total of 2, 4, or 8 weeks. Capillary permeability to albumin was assessed at the end of each dietary period by quantifying the extravasation of albumin-bound Evans blue (EB) dye in different organs. Unanesthetized animals were injected with Evans blue dye (20 mg/kg) in the caudal vein 10 min before being killed and EB dye was extracted by formamide from selected organs collected after exsanguination. As expected, rats had an increase in blood pressure upon feeding with fructose at 4 and 8 weeks (F, 149 ± 3 mm Hg; N, 139 ± 3 mm Hg; P < .05). Using this technique, we showed a 56% and a 51% reduction in capillary permeability in skeletal muscles at 4 and 8 weeks of fructose feeding, respectively (4 weeks: N, 44.5 ± 5.0 μg/g of dry tissue; F, 19.8 ± 4.2 μg/g of dry tissue; P < .01 and 8 weeks: N, 23.3 ± 3.7 μg/g of dry tissue; F, 11.3 ± 4.0 μg/g of dry tissue; P < .05). Similar changes were observed at 4 weeks in the thoracic aorta (N, 82.8 ± 8.8 μg/g of dry tissue; F, 53.0 ± 5.1 μg/g of dry tissue; P < .02) and skin (N, 36.0 ± 5.3 μg of dry tissue; F, 15.0 ± 2.3 μg/g of dry tissue; P < .02) and at 8 weeks in the liver (N, 107.5 ± 4.3 μg/g of dry tissue; F, 80.9 ± 3.2 μg/g of dry tissue; P < .01). In conclusion, fructose feeding is accompanied by a significant and selective reduction of Evans blue leakage primarily in skeletal muscle and liver, and transiently in the skin and aorta, consistent with a role for decreased tissue insulin delivery in insulin resistance.     

Impact of α- Versus β-Blockers on Hypertensive Target Organ Damage: Results of a Double-Blind,Randomized, Controlled Clinical Trial

In hypertensive disease, the extent of target organ damage determines the prognosis. We conducted a 6-month, double-blind randomized study to compare the effects of an α₁-adrenoreceptor blocker (bunazosin) with those of a β₁-adrenoreceptor blocker (metoprolol) on early hypertensive target organ damage at a similar level of blood pressure reduction. The study consisted of 43 patients (29 men and 14 women) of varying ages (mean age 52 ± 9 years) with essential hypertension World Health Organization stage I–II. Both the α- and the β-blocker lowered blood pressure to a similar extent measured by 24-h blood pressure monitoring. The left ventricular mass was comparably reduced in both cohorts (α-blocker 284 ± 80 v 259 ± 67 g, P < .05, β-blocker 282 ± 74 v 254 ± 70 g, P < .05). Treatment with the α-blocker led to reduced total peripheral resistance (22.9 ± 8.0 v 19.9 ± 5.3 U, P < .05), whereas therapy with the β-blocker resulted in an elevated total peripheral resistance (25.5 ± 8.4 v 28.5 ± 9.3 U, P < .10; P < .05 for the difference in both groups). Renal plasma flow remained constant in the α-blocker treated group but decreased in the β-blocker treated group (508 ± 141 v 477 ± 134 mL/min/1.73 m², P < .05). Glomerular filtration rate as measured by inulin clearance tended to increase after treatment with the α-blocker (112 ± 20 v 115 ± 18 mL/min/1.73 m², P < .10) in accordance with a decrease of serum creatinine (1.00 ± 0.14 v 0.93 ± 0.12 mg/dL, P < .001). Plasma cholesterol and LDL cholesterol was lowered after treatment with the α-blocker (238 ± 48 v 312 ± 37 mg/dL; P < .001, and 153 ± 32 v 130 ± 25 mg/dL; P < .05) while remaining unchanged in group treated with the β-blocker. Left ventricular hypertrophy was similarily reduced with α- and with β-blockade at a comparable reduction of 24-h blood pressure. α-Blockers effected a more favorable renal and systemic hemodynamic profile than β-blockers, but only long-term prospective studies will answer the question whether these hemodynamic effects result into a better cardiovascular prognosis.     

A low-calorie diet improves endothelium-dependent vasodilation in obese patients with essential hypertension

BackgroundBoth obesity and hypertension are associated with endothelial dysfunction. The purpose of this study was to investigate the effects of a low-calorie diet on endothelial function in obese patients with essential hypertension.MethodsWe measured forearm blood flow (FBF) during intra-arterial infusion of acetylcholine (ACh; 7.5, 15, 30 μg/min), an index of endothelium-dependent vasodilation, and isosorbide dinitrate (ISDN; 0.75, 1.5, 3.0 μg/min), an index of endothelium-independent vasodilation, in obese patients with essential hypertension before and after 2 weeks on a low-calorie diet (800 kcal/d). The study included 11 obese hypertensive Japanese patients (mean body mass index, 30.8 ± 3.6 kg/m²). Fifteen healthy Japanese normotensive individuals were recruited as a control group.ResultsIn obese patients with hypertension, the response of FBF to ACh was attenuated compared to healthy individuals (P < .001). Caloric restriction reduced body weight from 77.5 ± 15.0 to 73.2 ± 13.5 kg (P < .01), the mean blood pressure from 118.4 ± 8.7 to 105.7 ± 8.5 mm Hg (P < .01), fasting plasma insulin from 85.8 ± 22.8 to 64.8 ± 27.0 pmol/L (P < .05), serum total cholesterol from 5.30 ± 0.76 to 4.67 ± 0.58 mmol/L (P < .05), and low density lipoprotein cholesterol from 3.80 ± 0.48 to 3.29 ± 0.44 mmol/L (P < .05). Basal FBF was similar before and after weight reduction. Caloric restriction enhanced the response of FBF to ACh (P < .05), but did not alter the response to ISDN. The intra-arterial infusion of N^G-monomethyl-l-arginine (8 μmol/min), a nitric oxide synthase inhibitor, decreased the enhanced ACh-induced blood flow response induced by caloric restriction.ConclusionsThe present findings suggest that the caloric restriction improves endothelial-dependent vasodilation through an increased release of nitric oxide in obese hypertensive patients.     

Adipose triglyceride lipase expression in human adipose tissue and muscle. Role in insulin resistance and response to training and pioglitazone

Adipose triglyceride lipase (ATGL) catalyzes the first step in adipocyte and muscle triglyceride hydrolysis, and comparative gene identification-58 (CGI-58) is an essential cofactor. We studied the expression of ATGL and CGI-58 in human adipose and muscle and examined correlations with markers of muscle fatty acid oxidation. Nondiabetic volunteers were studied. Subjects with impaired glucose tolerance were treated with pioglitazone or metformin for 10 weeks. Subjects with normal glucose tolerance underwent a 12-week training program. We examined changes in ATGL and CGI-58 with obesity and insulin resistance, and effects of exercise and pioglitazone. Adipose triglyceride lipase messenger RNA (mRNA) expression showed no correlation with either body mass index or insulin sensitivity index in either adipose or muscle. However, adipose ATGL protein levels were inversely correlated with body mass index (r = −0.64, P < .02) and positively correlated with insulin sensitivity index (r = 0.67, P < .02). In muscle, ATGL mRNA demonstrated a strong positive relationship with carnitine palmitoyltransferase I mRNA (r = 0.82, P < .0001) and the adiponectin receptors AdipoR1 mRNA (r = 0.71, P < .0001) and AdipoR2 mRNA (r = 0.74, P < .0001). Muscle CGI-58 mRNA was inversely correlated with intramyocellular triglyceride in both type 1 (r = −0.35, P < .05) and type 2 (r = −0.40, P < .05) fibers. Exercise training resulted in increased muscle ATGL, and pioglitazone increased adipose ATGL by 31% (P < .05). Pioglitazone also increased ATGL in adipocytes. Adipose ATGL protein is decreased with insulin resistance and obesity; and muscle ATGL mRNA is associated with markers of fatty acid oxidation in muscle, as is CGI-58. The regulation of ATGL and CGI-58 has important implications for the control of lipotoxicity.     

Effects of α1-Blockade on the Forearm Vascular Resistance Responses to Lower Body Negative Pressure in Young Borderline Hypertensives

To determine whether α₁-blockade affects the forearm vascular resistance responses to lower body negative pressure (LBNP) in borderline hypertensives, six hypertensives (HTN; mean arterial pressure [MAP] = 109.9 ± 1.7 mm Hg, mean ± SE) and seven normotensives (NTN; MAP = 81.5 ± 1.4 mm Hg) underwent exposures of LBNP at pressures of −10, −20, and −40 mm Hg during systemic α₁-receptor blockade (BLK) and during placebo (PLA). Resting forearm vascular resistance (FVR) was greater in HTN than in NTN during PLA (34.8 ± 5.4 v 17.5 ± 3.1 units; P < .05), but not during BLK (28.1 ± 5.2 v 25.3 ± 9.9 units). When expressed as a percentage of resting FVR, LBNP evoked an increased FVR (P < .001) that did not differ significantly between BLK and PLA in either group. FVR was higher (P < .001) in HTN than in NTN throughout both trials; at −40 mm Hg of LBNP during BLK, the increase in FVR was greater (P < .05) in HTN than in NTN (131 ± 42 v 48 ± 15%). MAP (relative to resting) was maintained throughout LBNP during PLA but, at −40 mm Hg, was lower (P < .01) during BLK for both groups. HR was elevated in BLK and was increased at −40 mm Hg (P < .01) for each group in each trial. This increase was greater during BLK (P < .05). These data suggest that borderline hypertensives have a greater vasoconstrictor response to LBNP than do normotensives and α₁-blockade does not appear to attenuate this response.     

Angiotensin II stimulates left ventricular hypertrophy in hypertensive patients independently of blood pressure

Angiotensin II (AII) is known to be a growth stimulating factor for myocardial cells. We examined whether an exaggerated responsiveness to AII might aggravate left ventricular (LV) hypertrophy in human essential hypertension. To determine the responsiveness to AII in humans, we examined changes in mean arterial pressure (MAP), renal blood flow (RBF), and glomerular filtration rate (GFR) (steady state input clearance technique with para-aminohippurate and inulin, respectively) and aldosterone secretion to AII infusions (0.5 and 3.0 ng/kg/min) in 71 normotensive male and 48 hypertensive male subjects (age: 26 ± 3 years; 24-h ambulatory blood pressure: 121 ± 5/71 ± 4 mmHg v 138 ± 7/82 ± 7 mmHg, P < .001). In addition, each patient underwent two-dimensional guided M-mode echocardiography at rest to assess cardiac structure and function. When given AII 3.0, a greater increase of MAP (13 ± 7 v 17 ± 8 mm Hg, P < .022) and a more marked decrease of RBF (−203 ± 123 mL/min v −270 ± 137 mL/min, P < .007) were found in hypertensives than in normotensives, whereas changes in GFR and aldosterone concentration were similar in both groups. Most important, changes in GFR to AII correlated with echocardiographically determined LV mass (normotensives: AII 0.5: r = 0.33, P < .006, AII 3.0: r = 0.28, P < .05; hypertensives: AII 0.5: r = 0.41, P < .006, AII 3.0: r = 0.32, P < .05). After taking baseline MAP and body mass index into account, the increase in GFR to AII 0.5 in hypertensives still correlated with LV mass (partial r = 0.37, P < .01). Inasmuch as the increase of GFR is a marker of the responsiveness to AII (related to vasoconstriction at the postglomerular site), our data suggest that increased sensitivity to AII is linked to LV hypertrophy in early essential hypertension, independently of the level of blood pressure.     

Fructose and insulin sensitivity in patients with type 2 diabetes

Abstract. The effect of dietary fructose (20% of carbohydrate calories, 45–65 g day^?1 for 4 weeks) on glycaemic control, serum lipid, lipoprotein and apoprotein A-I and A-II concentrations and on insulin sensitivity was studied in 10 type 2 diabetic patients. The study was done in a randomized, double-blind fashion with crystalline fructose or placebo administered evenly during 4 meals or snacks per day. The patients were hospitalized throughout the study periods. The fasting plasma glucose concentration decreased during the fructose (from 10.7 ± 1.4 mmol l^?1 to 8.0 ± 0.8 mmol l^?1, P < 0.02) and the control diet (from 10.1 ± 0.9 mmol l^?1 to 8.0 ± 0.7 mmol l^?1 P < 0.05). The mean diurnal blood glucose concentration also fell both during the fructose (from 10.8± 0.5 mmol l^?1 to 8.4 ± 0.3 mmol l^?1, P < 0.001) and the control diet (from 10.3 ± 0.3 mmol l^?1 to 8.8 ± 0.9 mmol l^?1, P < 0.01). The HbA₁ concentration improved (P < 0.02) only during the fructose diet. Insulin sensitivity increased by 34% (P < 0.05) during the fructose diet, but remained unchanged during the control period. Serum insulin, triglyceride, apoprotein A-I and A-II concentrations, body weight, blood pressure and blood lactate remained unchanged during both diets. In conclusion, substitution of moderate amounts of fructose for complex carbohydrates can improve glycaemic control and insulin sensitivity in patients with type 2 diabetes.     

Failure of acute hyperinsulinemia to alter blood pressure is not due to baroreceptor feedback

It is well documented that acute insulin administration stimulates the sympathetic nervous system in both humans and animals. Despite marked sympathetic activation during acute hyperinsulinemia, blood pressure is generally not increased because it is overridden by the vasodilator action of insulin. The maintenance of blood pressure in the face of sympathetic activation is unknown. A possible mechanism includes feedback regulation by the baroreceptor reflex arc. In normotensive states, hyperinsulinemic-induced sympathetic activation may tend to elevate blood pressure, but this change is rapidly sensed by the baroreceptors in the carotid arteries (and aortic arch), and a counterbalancing increase in vasodilation could return blood pressure to normal. Thus, it can be speculated that, in the event of diminished baroreceptor sensitivity and suppressed vasodilator actions of insulin, common abnormalities in hypertension, acute insulin infusion would be expected to increase blood pressure.We undertook the present study to determine whether the baroreceptor reflex arc modulated the blood pressure response to acute hyperinsulinemia. To this end, six normotensive dogs underwent saline or insulin infusions before and after deactivation of the carotid and aortic baroreceptors. Baroreceptor dysfunction was documented after denervation in all cases by an abnormal response to phenylephrine injections. Before denervation, insulin infusions caused a slight but nonsignificant rise in mean arterial pressure (MAP; 110 ± 5 to 120 ± 5 mm Hg; P = 0.13). Baroreceptor denervation caused a marked variability in blood pressure. However, basal mean arterial pressure was not significantly altered. Neither saline nor insulin infusions (105 ± 10 v 105 ± 8 mm Hg, basal v steady state) caused a significant change in MAP in denervated dogs. Likewise, insulin and saline did not change heart rates significantly in intact or denervated animals. Furthermore, glucose metabolism was similar in both groups of animals. This study demonstrates that the baroreceptor reflex arc does not mediate the blood pressure response to acute hyperinsulinemia.     

Resistance to activated protein C and FV Leiden mutation in patients with a history of acute myocardial infarction or primary hypertension

This study was designed to investigate both resistance to activated protein C (APC-R) and the factor FV Q506 mutation incidence in patients with a history of acute myocardial infarction (AMI) and patients with primary hypertension (PH), a high-risk group for arterial thrombosis. Eighty patients with a history of AMI (group A), 160 patients with a history of PH (group B), and 124 age-matched controls without arterial disease (group C) were studied. APC-R was determined using the Coatest APC Resistance Kit of Chromagenix, Sweden. The prevalence of the FV Q506 mutation was estimated by DNA analysis (Bertina method). The prevalence of the FV Q506 mutation was 20%, 13.75%, and 8% in groups A, B, and C, respectively (A v C P = .0466). The prevalence of APC-R was 47.5% in group A v 13% in group C (P < .0001) and 36.25% in group B v 13% in group C (P < .0001). The response to activated protein C expressed as mean value ± SD was 2.05 ± 0.33 in group A v 2.56 ± 0.46 in group C (P < .05) and 2 ± 0.22 in group B v 2.56 ± 0.46 in group C (P < .05). These findings suggest that patients with a history of AMI or PH have a significantly increased incidence of both APC-R and FV Q506 mutation compared with the control group. These findings support the hypothesis that these anticoagulant defects may be risk factors for arterial thrombosis.     

Effects of l-arginine on blood pressure and metabolic changes in fructose-hypertensive rats

In the present study, we examined the effects of chronic l-arginine treatment on plasma insulin levels and systolic blood pressure (SBP) in fructose-fed (F) rats. Fructose feeding resulted in hyperinsulinemia and elevated blood pressure when compared with that in controls (plasma insulin, 311.3 ± 11.4 v control 164.4 ± 11.8 pmol/L, P < .05; SBP, 135.4 ± 4.2 v control 105.5 ± 1.3 mm Hg, P < .05). l-arginine treatment of fructose-hypertensive rats prevented the development of hyperinsulinemia and hypertension (plasma insulin, 200.1 ± 7.5 pmol/L; P < .05 compared with that in F rats; SBP, 108.0 ± 0.9 mm Hg; P < .05 compared with F rats). However, treatment with l-arginine did not influence any of these parameters in control rats. Statistical analysis of the data of plasma insulin level and SBP, revealed a significant correlation between these two variables. On the other hand, l-arginine treatment of F rats prevented the increased glucose and insulin concentrations in response to oral glucose challenge. l-arginine treatment also prevented the decrease in insulin sensitivity of F rats. These results indicate that l-arginine treatment is able to prevent fructose-induced hypertension and hyperinsulinemia. Our data also suggest a strong relationship between hyperinsulinemia and hypertension in this hypertensive rat model. Therefore, the antihypertensive effect of l-arginine could be, at least in part, the result of the restoration of plasma insulin levels by its vasodilator ability to increase blood flow to insulin sensitive tissues.