Vasomotor Responses Of Arteries Research Articles

Metformin does not Enhance Insulin‐Stimulated Vasodilation in Skeletal Muscle Resistance Arteries of the OLETF Rat

To test the hypothesis that chronic metformin treatment enhances insulin-induced vasodilation in skeletal muscle resistance arteries and arterioles. We assessed the effect of metformin treatment (from 20 to 32weeks of age) of obese Otsuka Long Evans Tokushima Fatty (OLETF) rats and lean LETO rats (300mg/kg) on insulin-stimulated vasodilation in isolated skeletal muscle feed arteries and arterioles. Metformin treatment significantly lowered food intake, body weight, percent body fat, and HbA1c in OLETF rats. Metformin resulted in a ~30% reduction in insulin-induced vasodilation of soleus feed arteries (SFA) from OLETF rats. Inhibition of endothelin-1 (ET-1) signaling produced 20% dilation and eliminated the difference between metformin-treated and untreated OLETF rats in insulin-induced dilation of SFA. In contrast to the SFA, metformin did not alter insulin-stimulated vasodilation in gastrocnemius feed arteries (GFA), or second-order arterioles in the red (G2A-R) or white (G2A-W) portions of the gastrocnemius muscle of OLETF rats. Metformin had no effects on vasomotor responses of arteries from LETO. Although metformin exerts favorable effects on body composition and HbA1c, it does not enhance the vasodilatory responses to insulin in the skeletal muscle feed arteries or arterioles of the obese OLETF rat.

Arginase blockade lessens endothelial dysfunction after thrombosis

Acute arterial thrombosis causes endothelial dysfunction due to decreased nitric oxide bioactivity. Increased arginase activity may modulate intracellular L-arginine levels, the substrate for nitric oxide. The purpose of this study was to identify the role of arginase in endothelial dysfunction in cell culture and in the vasomotor response of arteries exposed to thrombus. Rat aortic endothelial cells were exposed to thrombin at different time points. The cell extract was analyzed by immunoblotting and real-time polymerase chain reaction. Adult male rats underwent infrarenal aortic thrombosis by clip ligature for 1 hour. Infrarenal aortic ring segments were harvested and placed in physiologic buffer baths, and a force transducer was used to measure endothelial-dependent relaxation (EDR) and endothelial-independent relaxation (EIR). Arginase blockade was performed by incubating infrarenal aortic ring segments with arginase inhibitors for 1 hour before measuring EDR. Whole tissue extracts also underwent immunoblot analysis. The EDR and EIR curves were compared with analyses of variance. A 6.76 +/- 1.4-fold induction in arginase I message levels (P = .001) was found in rat aortic endothelial cells exposed to thrombin (30 U/mL), and arginase I protein levels increased 2.1 times. The eight infrarenal aortic ring segments exposed to thrombosis for 1 hour had diminished EDR curves compared with 14 nonthrombosed normal segments (controls). The maximum (+/- SEM) EDR (acetylcholine 10(-5)M dose) in control infrarenal aortic ring segments was 108% +/- 4.3% compared with 63% +/- 6.2% for thrombosed infrarenal aortic ring segments (P < .001). Exposure to arterial thrombosis resulted in a 3.8-times increase in arginase I protein levels in infrarenal aortic ring segments. Preincubation of nine infrarenal aortic ring segments with the nonspecific (difluoromethylornithine) and six with specific ([S]-[2-boronoethyl]-L-Cysteine-HCl [BEC]) arginase inhibitor for 1 hour significantly increased the maximum EDR compared with untreated thrombosed segments (104 +/- 5.2, 108 +/- 7.6 vs 63% +/- 6.2, P < .001). EDR curves for difluoromethylornithine- and BEC-treated infrarenal aortic ring segments were superimposed on control EDR curves. The EIR and the vasoconstriction with norepinephrine for all groups were similar. Endothelial cells exposed to thrombin have increased arginase I messenger RNA and protein levels. Arterial thrombosis causes endothelial dysfunction without affecting smooth muscle responsiveness. Arginase blockade can lead to normalization of arterial vasomotor function.

Relation of Cumulative Weight Burden to Vascular Endothelial Dysfunction in Obesity

Although excess fat mass is linked to increased cardiovascular risk, the relation between vascular phenotype and degree of obesity in high weight categories is unknown. We examined brachial artery vasomotor responses using ultrasound in 203 consecutive patients with severe obesity (mean age 44 +/- 11 years; body mass index [BMI] 46 +/- 9 kg/m(2), range 30 to 72; and body weight 128 +/- 29 kg, range 69 to 207). We studied a unique population in which 71% of subjects were characterized as morbidly obese (BMI > or =40 kg/m(2)), which included a 31% group of super-obese subjects (BMI > or =50 kg/m(2)). Brachial artery flow-mediated dilation (FMD) and nitroglycerin-mediated dilation were examined as measures of endothelium-dependent and -independent dilation, respectively, in relation to clinical, hemodynamic, and metabolic variables. Endothelial function was significantly impaired in the highest compared with the lowest tertile of body weight (FMD 6.5 +/- 4.6% vs 9.8 +/- 4.8%, p <0.001), whereas nitroglycerin-mediated dilation was similar in all groups. Univariate correlates of FMD were gender, weight, waist circumference, BMI, diastolic blood pressure, and creatinine. In multivariate analysis, weight was a strong independent significant predictor of FMD (beta = -0.23, p = 0.005) in addition to gender. Within an overweight population, cumulative weight burden remains strongly linked to progressive arterial dysfunction. In conclusion, these results suggest that cardiovascular risks intensify with higher degrees of obesity and underscore the importance of therapeutic weight loss interventions.

Differences in resistance artery vasomotor responses in the hypertensive hamster

This study examined whether vasomotor responses in resistance arteries were different between normotensive (CHF-148) and hypertensive hamsters (CHF-H4). Resistance arteries were isolated, cannulated, and pressurized to 80 mm Hg. Thereafter, their concentration-response relationship to endothelial-dependent dilators, endothelial-independent dilators and constrictors was determined. Maximal dilatory (Ca free PBS) and constrictor (65 mM KCl) responses were determined. Dilatory responses to endothelial-dependent (acetylcholine and vasoactive intestinal peptide) and -independent (adenosine and sodium nitroprusside) agonists were not different between strains. However, endothelial-independent responses was <50% of maximal dilation at mM doses. These submaximal responses reflected a diminished response downstream of cGMP (mM 8Br-cGMP elicited ~25% dilation). With respect to constrictors, responses to KCl, norepinephrine, and endothelin-1 were similar between strains. However, angiotensin II (AngII) constriction was amplified in the hypertensive hamster through the AT-1 receptor (losartan 10 μM). At higher AngII concentrations (>3 nM), vessels relaxed via concentration-dependent desensitization. The importance of AngII to the hypertension was evident when losartan infusion (60 mg/kg body weight) normalized blood pressure in the hypertensive hamster. As the hypertensive hamster is a high renin model of hypertension, the greater constriction of the resistance vasculature to AngII likely contributes to the elevated blood pressure in this model of hypertension.

Role of cyclic ADP-ribose in Ca 2+-induced Ca 2+ release and vasoconstriction in small renal arteries

Cyclic-ADP-ribose (cADPR) has been reported to serve as a second messenger to mobilize intracellular Ca 2+ independent of IP 3 in a variety of mammalian cells. This cADPR-mediated Ca 2+ signaling pathway importantly participates in the regulation of various cell functions. The present study determined the role of endogenous cADPR in mediating ryanodine-sensitive Ca 2+-induced Ca 2+ release (CICR) in vascular myocytes from small renal arteries and vasomotor response of these arteries. In freshly-isolated renal arterial myocytes, addition of CaCl 2 (0.01, 0.1, and 1 mM) into the Ca 2+-free bath solution produced a rapid Ca 2+ release response from the sarcoplasmic reticulum (SR), with a maximal increase of 237 ± 25 nM at 1 mM CaCl 2. This CaCl 2 response was significantly blocked by a cell-membrane permeant cADPR antagonist, 8-bromo-cADP-ribose (8-br-cADPR) (30 μM) or ryanodine (50 μM). Caffeine, a classical CICR or ryanodine receptor activator was found to stimulate the SR Ca 2+ release (Δ[Ca 2+] i: 253 ± 35 nM), which was also attenuated by 8-br-cADPR or ryanodine. Using isolated and pressurized small renal arteries bathed with Ca 2+-free solution, both CaCl 2 and caffeine-induced vasoconstrictions were significantly attenuated by either 8-br-cADPR or ryanodine. Biochemical analyses demonstrated that CaCl 2 and caffeine did not increase cADPR production in these renal arterial myocytes, but confocal microscopy showed that a dissociation of the accessory protein, FK506 binding protein 12.6 (FKBP12.6) from ryanodine receptors was induced by CaCl 2. We conclude that cADPR importantly contributes to CICR and vasomotor responses of small renal arteries through enhanced dissociation of ryanodine receptors from their accessory protein.

Functional reconstitution of endothelial nitric oxide synthase reveals the importance of serine 1179 in endothelium-dependent vasomotion.

Phosphorylation of endothelial nitric oxide synthase (eNOS) at serine 1179 can activate the enzyme, leading to NO release. Because eNOS is important in regulating vascular tone, we investigated whether phosphorylation of this residue is involved in vasomotion. Adenoviral transduction of endothelial cells (ECs) with the phosphomimetic S1179DeNOS markedly increased basal and vascular endothelial cell growth factor (VEGF)-stimulated NO release compared with cells transduced with wild-type virus. Conversely, adenoviral transduction of ECs with the non-phosphorylatable S1179AeNOS suppressed basal and stimulated NO release. Using a novel method for luminal delivery of adenovirus, transduction of the endothelium of carotid arteries from eNOS knockout mice with S1179DeNOS completely restored NO-mediated dilatation to acetylcholine (ACh), whereas vasomotor responses in arteries transduced with S1179AeNOS were significantly attenuated. Basal NO release was also significantly reduced in arteries transduced with S1179AeNOS, compared with S1179DeNOS. Thus, our data directly demonstrate that phosphorylation of eNOS at serine 1179 is an important regulator of basal and stimulated NO release in ECs and in intact blood vessels.

Estrogen Replacement Reverses Endothelial Dysfunction in Postmenopausal Women

Purpose: To measure the effect of long-term clinical hormone replacement therapy on brachial artery vasomotor responses, and to compare these responses in premenopausal and postmenopausal women. Patients and Methods: We studied 23 postmenopausal women, including 18 who were evaluated prior to starting clinically indicated oral hormone replacement therapy. Twelve postmenopausal women received estrogen alone, the other 6 were treated with estrogen/medroxyprogesterone combinations. Eleven premenopausal volunteers served as a comparison group. Change in brachial artery diameter in response to postischemic hyperemic flow and sublingual nitroglycerin was measured by ultrasound. Results: The 18 postmenopausal subjects receiving hormone replacement showed a progressive improvement in their postischemic vasodilation. Mean (±SD) postischemic vasodilation was 0.4% ± 7.1% prior to estrogen replacement. There were significant increases in postischemic vasodilation of 4.8% ± 6.6% after 1 month and 8.3% ± 3.4% after 6 months of estrogen replacement. The response to nitroglycerin was similar at all time points studied. Women with the most abnormal responses to hyperemic flow at baseline demonstrated the greatest improvement after 6 months of hormone replacement therapy. Premenopausal and postmenopausal subjects differed in their response to hyperemic flow, with premenopausal women showing 5.8% vasodilatation compared with a 0.6% vasodilation in postmenopausal women ( P = 0.046). Conclusions: Endothelial function is abnormal in many postmenopausal women compared with premenopausal women, and in some postmenopausal women it can be enhanced by estrogen replacement therapy. This effect may increase with prolonged use.

Determinants of coronary artery reactivity in premenopausal female cynomolgus monkeys with diet-induced atherosclerosis.

The purpose of this study was to identify determinants of coronary artery reactivity among premenopausal female monkeys. Estrogen replacement therapy in postmenopausal females modulates reactivity of atherosclerotic coronary arteries. However, no studies have evaluated the factors that modulate coronary artery reactivity among premenopausal females. Twenty-five adult premenopausal female monkeys were fed an atherogenic diet for 32 months. During this time, monkeys were housed in small social groups and determined to be socially dominant (associated with normal ovarian function) or subordinate (associated with impaired ovarian function). After 32 months, coronary artery vasomotor responses to intracoronary acetylcholine, nitroglycerin, and serotonin were assessed by computer-assisted quantitative coronary angiography. Coronary arteries of dominant monkeys dilated (+9 +/- 2%), whereas those of subordinate monkeys constricted (-6 +/- 2%) in response to acetylcholine (P < .05). There was no effect of social status on vascular response to nitroglycerin or serotonin (P > .10). Vascular responses to acetylcholine were independent of social status effects on plasma lipids, blood pressure, and atherosclerosis extent. The correlation between acetylcholine responses and plasma estradiol concentration measured on the day of angiography was r = .7 (P = < .01). Furthermore, dilation occurred only if plasma estradiol concentrations were greater than 60 pg/mL. Psychosocial factors and endogenous estrogen production are important modulators of acetylcholine-mediated dilation of atherosclerotic coronary arteries among premenopausal female monkeys.

Role of vascular endothelium in exercise-induced dilation of large epicardial coronary arteries in conscious dogs.

The role of vascular endothelium in the control of epicardial coronary artery vasomotion during treadmill exercise remains unclear. Therefore, we examined the consequences of in vivo balloon endothelial denudation on external coronary diameter of the left circumflex artery during exercise in conscious dogs. Seven dogs instrumented for the measurement of arterial blood pressure, external coronary artery diameter, and coronary blood flow were studied during exercise before and up to 21 days after balloon endothelial denudation of the proximal left circumflex artery. Endothelial denudation was confirmed by abolition of the epicardial coronary artery dilation induced by acetylcholine (0.3 microgram/kg IV) and reactive hyperemia. Epicardial coronary vasodilation was observed in the control state during treadmill exercise (+5.2 +/- 1.0%). In contrast, a marked vasoconstriction was observed 3 (-4.6 +/- 0.6%) and up to 6 days after endothelial denudation. Complete epicardial coronary artery dilation in response to acetylcholine and exercise was restored 9 days after endothelial denudation. In addition, epicardial coronary artery vasomotor responses to acetylcholine and treadmill exercise were closely correlated (r = .82, P < .001). Reactive dilation was not completely restored 21 days after endothelial denudation, but reactive hyperemia and exercise vasomotor responses during the 21 days follow-up were correlated (r = .70, P < .001). Vasodilation induced by nitroglycerin (1 microgram/kg IV) was reduced by 25% (P < .01) 3 days after endothelial denudation and returned to its corresponding control level 3 days later. Prazosin (50 micrograms/kg IV) significantly attenuated the exercise-induced coronary artery constriction after endothelial denudation (+1.5 +/- 1.4% versus -4.6 +/- 1.0%). These data demonstrate that endothelium is essential for the mediation of epicardial coronary dilation during exercise and may protect these vessels against the vasoconstrictor effect of endogenous catecholamines.

Effects of Sodium Pentothal and Sufentanil on Serotonin Induced Constriction of Canine Coronary Artery Rings Without Endothelium

Abstract 1. 1. The individual and combined effects of sufentanil and sodium pentothal on canine coronary artery vasomotor responses to 5-HT were studied in an isolated vascular ring preparation. 2. 2. Clinical concentrations of sufentanil have little effect on basal coronary tension or constriction induced by either 5-HT or sodium pentothal individually, until very high doses > 0.26 μM are reached. 3. 3. Sodium pentothal causes coronary constriction at clinical concentrations and this effect is additive and possibly potentiated when combined with 5-HT. 4. 4. Sufentanil inhibits coronary constriction induced by the combination of sodium pentothal and 5-HT.

Effects of sodium pentothal and sufentanil on serotonin induced constriction of canine coronary artery rings without endothelium

1. 1. The individual and combined effects of sufentanil and sodium pentothal on canine coronary artery vasomotor responses to 5-HT were studied in an isolated vascular ring preparation. 2. 2. Clinical concentrations of sufentanil have little effect on basal coronary tension or constriction induced by either 5-HT or sodium pentothal individually, until very high doses > 0.26 μM are reached. 3. 3. Sodium pentothal causes coronary constriction at clinical concentrations and this effect is additive and possibly potentiated when combined with 5-HT. 4. 4. Sufentanil inhibits coronary constriction induced by the combination of sodium pentothal and 5-HT.

The feline carotid rete: vasomotor reactivity of isolated arteries.

Vasomotor responses of arteries from the feline carotid rete were examined using a sensitive in vitro system. The vessel segments constricted in response to several vasoactive agents and putative neurotransmitters. Sympathomimetic agents (noradrenaline, adrenaline, oxymetazoline, phenylephrine), 5-hydroxytryptamine, histamine, angiotensin II, and prostaglandin F2 alpha all induced concentration-dependent contractile responses. The contractions induced by noradrenaline, 5-hydroxytryptamine, and histamine could be antagonized by phentolamine, methysergide, and mepyramine, respectively. Cholinomimetics (acetylcholine, carbacholine), vasoactive intestinal peptide and papaverine induced potent dilatory responses. The effect of carbacholine was shifted towards higher agonist concentrations by atropine. Dilatations, though small in magnitude, were found by application of adenosine, isoproterenol, and histamine. These results correlate well with the recent demonstration of autonomic nerves and indicate the occurrence of corresponding receptor sites in the walls of the carotid rete arteries.