Impaired endothelium-dependent and independent vasodilation in patients with Type 2 (non-insulin-dependent) diabetes mellitus

Summary The endothelium plays a pivotal role in modulating the reactivity of vascular smooth muscle through the formation of several vasoactive substances. We examined the effects of endothelium-dependent and independent vasodilators on forearm blood flow in 29 patients with Type 2 (non-insulin-dependent) diabetes mellitus and in 21 control subjects, using venous occlusion plethysmography. Via a brachial artery cannula, increasing amounts of acetylcholine and glyceryl trinitrate were infused in doses of 60, 120, 180 and 240 mmol per min and 3, 6 and 9 nmol per min respectively. N^G monomethyl-l-arginine, a stereospecific inhibitor of endothelium derived relaxing factor, was infused to inhibit basal and stimulated release of this dilator substance. Reactive hyperaemic forearm blood flow did not differ between groups. Forearm blood flow responses to each dose of acetylcholine were significantly greater in control than diabetic subjects (p<0.01 for all doses). N^G monomethyl-l-arginine attenuated forearm blood flow from maximal stimulated values when responses were compared with the natural decline to acetylcholine in forearm flow in both control and diabetic subjects (p<0.05 for both groups), but had no effect on basal blood flow responses. Forearm blood flow responses to each dose of glyceryl trinitrate were significantly greater in control than diabetic subjects (p<0.05 for all). These data provide evidence for endothelial and smooth muscle dysfunction in diabetes which may have important therapeutic implications.     

Abnormal vascular responses in human chronic cardiac failure are both endothelium dependent and endothelium independent

Objective—To study underlying vascular responses in chronic heart failure in patients without ACE inhibitor treatment, and to compare them with age matched controls.
Design—Forearm blood flow was studied using venous occlusion plethysmography in patients with chronic heart failure (n = 12) and matched controls (n = 13), after infusion of L-NMMA (a nitric oxide synthase inhibitor), glyceryl trinitrate (an endothelium independent vasodilator), and serotonin (an endothelium dependent vasodilator).
Results—L-NMMA produced significant vasoconstriction in normal subjects (forearm blood flow reduced by 24%), but not in patients (6%; difference between groups p < 0.03). The vasodilator responses to glyceryl trinitrate were impaired in patients (p < 0.02). In normal controls, serotonin produced initial dilatation, followed by vasoconstriction at high doses. In patients, no vasodilator responses were observed, only late vasoconstriction (p < 0.03).
Conclusions—The vascular responses of patients are confirmed as being abnormal. The lack of response to L-NMMA suggests that nitric oxide does not contribute to basal vascular tone in patients with chronic heart failure. The responses to glyceryl trinitrate and to serotonin suggest that there is both smooth muscle and endothelial dysfunction in patients with chronic heart failure.

Keywords: heart failure;  endothelium;  nitrates;  serotonin     

Cyclosporine A and control of vascular tone in the human forearm: influence of post-transplant hypertension

OBJECTIVE: The use of cyclosporine A after organ transplantation is associated with a high incidence of hypertension, but the underlying mechanisms for this process are not clear. We investigated the effects of blockade of basal release of endothelial nitric oxide and the effects of endothelium-independent and -dependent vasodilators and vasoconstrictors in patients treated with cyclosporine A after heart transplantation. DESIGN: We measured blood pressure and forearm blood flow responses to brachial artery infusions of NG-monomethyl-L-arginine (L-NMMA), sodium nitroprusside, acetylcholine, norepinephrine and vasodilating and vasoconstricting doses of endothelin-1 in eight patients early (< 3 months) and in 11 patients late (> 18 months) after transplantation. RESULTS: Diastolic blood pressure was higher late after transplantation, but calculated forearm vascular resistance was lower (P < 0.01). Thus, increased forearm vascular resistance does not contribute to the increase in blood pressure. The vasoconstrictor response to L-NMMA was similar in both groups but a reduced endothelium-dependent vasodilator response to acetylcholine was seen late after transplantation. However, impaired smooth muscle responsiveness to nitric oxide may have contributed to this finding, since the response to sodium nitroprusside tended to be reduced. Vasoconstrictor responses to norepinephrine and endothelin-1 were comparable but no vasodilation was seen with low doses of endothelin-1 late compared with early after transplantation (P < 0.05). CONCLUSIONS: The findings in the forearm circulation question the concept of generalized increases in vasoconstrictor responses or a disturbance of tonic, basal release nitric oxide in the pathogenesis of cyclosporine-A-induced hypertension. Although the forearm vasodilator responses to the stimulation of endothelial nitric oxide production and release by acetylcholine, and to low doses of endothelin-1, were impaired, these findings could be explained by the increase in blood pressure rather than cyclosporine A itself.     

Reversal by L-arginine of a dysfunctional arginine/nitric oxide pathway in the endothelium of the genetic diabetic BB rat

Summary We examined the effects of acute supplementation with arginine in vitro on endothelium-dependent relaxation in aortic rings taken from female genetic, diabetes-prone BB rats. Sensitivity to norepinephrine-induced contraction was unaltered in rings of diabetic BB rats compared to rings from non-diabetic littermates. In precontracted rings, acetylcholine produced a concentration-dependent relaxation which was impaired by diabetes. This relaxation was blocked by l-nitroarginine in both control and diabetic rings. Addition of 3 mmol/l l-arginine (but not d-arginine) enhanced relaxation in diabetic rings similar to that seen in control rings without arginine. l-arginine had no effect on acetylcholine-induced relaxation in control rings. In contrast, relaxation-induced by nitroglycerin in diabetic rings without endothelium was not altered by l-arginine treatment. Thus, a defect in the utilization of arginine by nitric oxide synthase exists in the endothelium of the diabetic BB rat. [Diabetologia (1997) 40: 910–915] Received: 24 February 1997 and in revised form: 17 April 1997     

Tetrahydrobiopterin improves endothelium-dependent vasodilation by increasing nitric oxide activity in patients with Type II diabetes mellitus

Aims/hypothesis. Tetrahydrobiopterin is an essential cofactor of nitric oxide synthase, and its deficiency decreases nitric oxide bioactivity. Our aim was to find whether supplementation of tetrahydrobiopterin could improve endothelial dysfunction in diabetic patients.¶Methods. Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine (0.75– 3.0 μg · 100 ml^–1· min^–1) and to the endothelium-independent vasodilator sodium nitroprusside (0.1–1.0 μg · 100 ml^–1· min^–1) before and during concomitant intra-arterial infusion of tetrahydrobiopterin (500 μg/min) were measured by venous occlusion plethysmography in 12 control subjects and 23 patients with Type II (non-insulin-dependent) diabetes mellitus.¶Results. In control subjects, tetrahydrobiopterin had no effect on the dose-response curves to acetylcholine and sodium nitroprusside. In contrast, in diabetic patients, the attenuated endothelium-dependent vasodilation to acetylcholine was considerably improved by concomitant treatment with tetrahydrobiopterin, whereas the endothelium-independent vasodilation was not affected. This beneficial effect of tetrahydrobiopterin in diabetic patients could be completely blocked by N ^G-monomethyl-l-arginine.¶Conclusion/interpretation. These findings suggest the possibility that endothelial dysfunction in Type II diabetes might be related to decreased availability of tetrahydrobiopterin. [Diabetologia (2000) 43: 1435–1438]     

5-Hydroxytryptamine mediates endothelium dependent coronary vasodilatation in the isolated rat heart by the release of nitric oxide

STUDY OBJECTIVE--The aim was to investigate further the endothelium dependent vasodilator action of 5-hydroxytryptamine (5-HT) on the rat coronary circulation. DESIGN--Using saponin to damage the endothelium and L-NMMA (NG-monomethyl-L-arginine), the selective inhibitor of nitric oxide formation, we examined the role of endothelium and nitric oxide in causing 5-HT induced vasodilatation in the isolated rat heart. EXPERIMENTAL MATERIAL--56 rat hearts were excised and perfused on a Langendorff preparation. MEASUREMENTS AND MAIN RESULTS--5-HT at (10(-9) to 10(-5) M) and glyceryl trinitrate at (10(-5) to 10(-3) M) (n = 24) induced a dose dependent increase in coronary flow. Chemical removal of the endothelium by exposure to saponin (30 micrograms.ml-1) (n = 8) abolished the 5-HT induced vasodilatation but had no effect on the response to glyceryl trinitrate. Pretreatment of rats (n = 8) with L-NMMA (100 mg.kg-1) unmasked a strong vasoconstrictor effect of 5-HT but did not affect the glyceryl trinitrate induced vasodilatation. Perfusion of L-NMMA pretreated hearts with L-arginine at 10(-4) M (n = 8) restored the vasodilatation induced by 5-HT but L-arginine perfusion had no effect on the extent of 5-HT or glyceryl trinitrate induced vasodilatation in normal hearts (n = 8). CONCLUSIONS--In the coronary circulation of the isolated rat heart, 5-HT mediates its vasodilator effect via endothelium dependent release of nitric oxide.     

Treatment of Chronic Anal Fissure by Application of l-Arginine Gel: A Phase II Study in 15 Patients

PURPOSE Local application of exogenous nitric oxide donors, such as isosorbide dinitrate and glyceryl trinitrate, promotes fissure healing by reducing anal resting pressure and improving anodermal blood flow. The major drawback of these nitric oxide donors is headache. The overall incidence of this side effect is approximately 40 percent. Recently we have shown in healthy volunteers that l-arginine, being an intrinsic precursor of nitric oxide, reduces anal resting pressure without headache as a side effect. The aim of the pres-ent study was to evaluate the effect of l-arginine on anal resting pressure, anodermal blood flow, and fissure healing in patients with chronic anal fissure.METHODS Fifteen patients with a chronic anal fissure were included in the present study. Before entering the study 10 patients were unsuccessfully treated by local application of isosorbide dinitrate. Six of these patients experienced severe headache during treatment with isosorbide dinitrate. All patients were treated for at least 12 weeks by local application of a gel containing l-arginine 400 mg/ml five times a day. In patients with a persistent fissure, treatment was continued until 18 weeks. Anal manometry and laser Doppler flowmetry of the anoderm were performed before treatment, 20 minutes after local application of the first dose, and after 12 weeks of treatment. A visual analog scale was used to assess fissure-related pain and headache.RESULTS One patient dropped out after one day of treatment, and one was excluded because of violation of the study protocol. After 12 weeks of treatment complete fissure healing was observed in 3 of 13 (23 percent) patients, and after 18 weeks the healing rate was 8 of 13 (62 percent) patients. None of the 13 patients experienced typical nitric oxide-induced headache. The pressure recordings showed a significant reduction of maximum anal resting pressure (mean ± SD): pretreatment 89 ± 17 mmHg; 20 minutes after application of the first dose 67 ± 17 mmHg; 12 weeks after treatment 74 ± 14 mmHg (P < 0.005). Recordings of anodermal blood flow showed a significant increase in flow: pretreatment 0.36 ± 0.25 volts; 20 minutes after application of the first dose 0.59 ± 0.27; 12 weeks after treatment 0.64 ± 0.33 (P < 0.005).CONCLUSIONS Local application of l-arginine promotes fissure healing without headache as a side effect, and l-arginine is effective even in patients not responding to isosorbide dinitrate treatment.Norgine Research Ltd. Northwood, United Kingdom, financially supported the study.Reprints are not available.Read at the annual meeting of The American Society of Colon and Rectal Surgeons, Chicago, Illinois, June 3 to 8, 2002.     

Effects of exercise training on conduit and resistance vessel function in treated and untreated hypercholesterolaemic subjects.

AIMS: Despite the importance of both lipid metabolism and physical activity to cardiovascular health, few studies have examined the effect of exercise training on vascular function in hypercholesterolaemic humans. METHODS AND RESULTS: A randomized, cross-over design investigated the effect of 8 weeks of combined aerobic and resistance exercise training on conduit and resistance vessel function in 11 untreated subjects with hypercholesterolaemia and 11 subjects taking lipid-lowering medication. High-resolution vascular ultrasonography following forearm ischaemia and glyceryl trinitrate administration determined conduit vessel endothelium-dependent and independent function. Strain-gauge plethysmography, with intra-aerial infusions of acetylcholine, sodium nitroprusside and N(G)-monomethyl-L-arginine, determined resistance vessel function. Flow-mediated dilation and the forearm blood flow response to acetylcholine improved significantly following training in the treated subgroup (both P<0.05) but not the untreated, although the blood flow response to N(G)-monomethyl-L-arginine was augmented following training in the untreated subjects (P<0.05), indicating greater basal nitric oxide bioactivity. Training did not alter responsiveness to glyceryl trinitrate or sodium nitroprusside. CONCLUSIONS: Combined aerobic and resistance training improves endothelium-dependent conduit and resistance vessel function in hypercholesterolaemic subjects taking lipid-lowering medications and basal nitric oxide bioactivity in untreated hypercholesterolaemic subjects. Exercise training may provide additional cardiovascular benefits for hypercholesterolaemic patients including those taking lipid-lowering medication.     

Chronic vitamin E treatment prevents defective endothelium-dependent relaxation in diabetic rat aorta

Summary We examined the effect in rats of 2 months of streptozotocin-induced diabetes mellitus on relaxation and contraction of aortas in vitro. A further diabetic group was treated from time of diabetes induction with a 1% dietary supplement of vitamin E. Diabetes caused a 26.5% deficit (p<0.001) in maximum endothelium-dependent relaxation to acetylcholine in phenylephrine-precontracted aortas. This was 64.3% attenuated (p<0.01) by vitamin E treatment; maximum relaxation was not significantly altered compared to non-diabetic rats. Vitamin E treatment of non-diabetic rats did not significantly affect acetylcholine-induced relaxation. Diabetes or treatment did not significantly alter acetylcholine sensitivity. Endothelium-independent relaxation response to glyceryl trinitrate was not affected by diabetes or vitamin E treatment, indicating that vascular smooth muscle responses to nitric oxide remained unaltered. There was a 35.4% reduction in the maximum contractile response to phenylephrine with diabetes (p<0.05) which was unaffected by vitamin E treatment. The data suggest that the chronic deficit in nitric oxide-mediated endothelium-dependent relaxation in diabetes depends largely upon excess activity of reactive oxygen species. Treatment with vitamin E to increase free radical scavenging specifically protected vascular endothelium although it had no effect on deficits in vascular smooth muscle contractile responses.Abbreviations NO Nitric oxide - ARI aldose reductase inhibitor - ACH acetylcholine - GTN glyceryl trinitrate - GSH reduced form of glutathione - EC₅₀ effective concentration for 50% of the maximal response     

Nitric oxide synthesised from L-arginine mediates endothelium dependent dilatation in human veins in vivo

Endothelium derived relaxing factor (EDRF) has been identified as nitric oxide, synthesised from the amino acid L-arginine, a process which is inhibited by the L-arginine analogue NG-monomethyl L-arginine (L-NMMA). We have studied the effect of local infusions of L-NMMA on venous reactivity in healthy volunteers. Studies were performed using the veins on the back of the hand. The diameter of a single dorsal hand vein was measured in healthy subjects who had taken 600 mg of aspirin 30 min before the experiment. Changes in diameter were recorded during local infusions of noradrenaline, bradykinin, acetylcholine, glyceryl trinitrate, L- and D-arginine and its NG-monomethyl derivatives. L-NMMA (100 nmol.min-1) stereospecifically inhibited vasodilatation induced by acetylcholine and bradykinin (p less than 0.02) but not that induced by the endothelium independent vasodilator glyceryl trinitrate. L-NMMA (100 nmol.min-1) potentiated the venoconstrictor effect of a high dose of acetylcholine (100 nmol.min-1) without affecting the action of noradrenaline and without having a direct venoconstrictor effect in doses up to 10 mumol.min-1. These results show that the venous effects of certain vasodilators in man are mediated through the release of nitric oxide (EDRF) synthesised from L-arginine. They also highlight differences in basal and stimulated production of nitric oxide between arteries and veins.     

Changes in endothelium-dependent vasodilatation and alpha-adrenergic responses in resistance vessels during the menstrual cycle in healthy women

During the menstrual cycle, changes in endothelium-dependent vasodilatation have been demonstrated in conduit vessels in vivo, but responses in resistance vessels have not been studied. The aim of this study was to examine endothelium-dependent vasodilatation, the effects of local nitric oxide synthesis, and alpha-adrenergic constriction in resistance vessels during the menstrual cycle in 15 healthy female volunteers (mean age, 28.07 +/- 2.1 yr). Forearm blood flow in response to intrabrachial infusion of bradykinin (10, 30, and 100 pmol/min; endothelium-dependent vasodilator), glyceryl trinitrate (4, 8, and 16 nmol/min; endothelium-independent vasodilator), noradrenaline (60, 120, and 240 pmol/min; alpha-adrenergic receptor agonist), and N(G)-monomethyl-L-arginine (1, 2, and 4 micromol/min; nitric oxide synthase inhibitor) was assessed by venous occlusion plethysmography. All subjects were studied in early menstrual phase (days 1--4) and midcycle (days 10-13). Vasodilator response to bradykinin, expressed as the within-subject mean difference in the area under the dose-response curve between phases, was significantly increased at midcycle compared with that in the early menstrual phase (486.5 +/- 165.0; P = 0.01), whereas there was no significant difference in response to glyceryl trinitrate (185.8 +/- 239.0; P = 0.45). The vasoconstrictor response to noradrenaline was significantly greater at midcycle (97.1 +/- 39.4; P = 0.027), but the response to N(G)-monomethyl-L-arginine was not significantly different (17.5 +/- 35.2; P = 0.63). Serum estradiol was approximately 3-fold higher at midcycle, with a mean difference of 252.3 +/- 56.0 pmol/L (P = 0.0005). Progesterone concentrations were not significantly different (-0.11 +/- 0.1 nmol/L; P = 0.28). Differences in endogenous estrogen levels between menstrual phases may underlie changes in bradykinin and noradrenaline responses. If exogenous estrogens have similar effects, the balance of these two opposing actions may determine whether estrogen replacement in postmenopausal women has beneficial or harmful effects on the vasculature.     

Insulin secretion in rats with chronic nitric oxide synthase blockade

Summary Nitric oxide, which is produced from l-arginine by a nitric oxide-synthase enzyme, has been shown to be a ubiquitous messenger molecule. Recently, it has been suggested that nitric oxide might influence insulin secretion by activating the soluble guanylate cyclase and generating cyclic guanosine monophosphate (cGMP). We have investigated the role of the nitric oxide pathway in insulin secretion by evaluating the insulin response to several secretagogues in rats in which nitric oxide-synthase was chronically inhibited by oral administration of the l-arginine analogue, N^G-nitro-l-arginine methyl ester (l-NAME). Blood pressure and aortic wall cGMP content were used as indices of nitric oxide-synthase blockade. Insulin secretion was evaluated after an intravenous bolus of d-glucose, l-arginine or d-arginine. Chronic l-NAME administration induced a 30% increase in blood pressure and a seven-fold drop in arterial cGMP content. Body weight, fasting plasma glucose and insulin were not influenced by l-NAME administration. First-phase insulin secretion (1+3 min) in response to glucose was not significantly different in l-NAME and control rats. The areas under the insulin curve were similar in both groups. Insulin secretion in response to d-arginine or l-arginine in l-NAME-treated and control rats were also similar. In conclusion, chronic nitric oxide-synthase blockade increases blood pressure and decreases aortic cGMP content, but does not alter insulin secretion in response to several secretagogues. Chronic oral administration of l-NAME in the rat provides an adequate animal model for studying the l-arginine nitric oxide-pathway.Abbreviations NO Nitric oxide - cGMP guanosine 3: 5 cyclic monophosphate - l-NMMA N^G-monomethyl-l-arginine - l-NAME N^G-nitro-l-arginine-methyl-ester - NOD mice non obese diabetic mice     

The impaired renal vasodilator response attributed to endothelium-derived hyperpolarizing factor in streptozotocin – induced diabetic rats is restored by 5-methyltetrahydrofolate

Aims/hypothesis. Endothelial dysfunction contributes to the development of diabetic vascular complications. A better understanding of the pathophysiology of endothelial dysfunction in diabetes could lead to new approaches to prevent microvascular disease. Methods. Endothelium-dependent and endothelium-independent vasodilator responses were investigated in the renal microcirculation of streptozotocin-induced diabetic rats. We measured renal blood flow changes with an electromagnetic flow probe. In addition, the responses of the different segments of the renal microcirculation were evaluated with videomicroscopy using the hydronephrotic kidney technique. Because endothelial cells release different relaxing factors (nitric oxide, prostacyclin and an unidentified endothelium-derived hyperpolarizing factor), responses to acetylcholine were measured before and after treatment with the nitric oxide synthase inhibitor l-N ^G-nitroarginine methylester HCI (l-NAME) and the cyclooxygenase inhibitor indomethacin. We evaluated with the effect of 5-methyltetrahydrofolate, the active form of folate, on the responses. Results. The l-NAME- and indomethacin-resistant vasodilation to intra-renal acetylcholine was significantly reduced in the diabetic compared with control rats, suggesting impaired endothelium-derived hyperpolarizing factor-mediated vasodilation. The responses to the nitric oxide donor (Z)-1-[-2-(aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate) and to the K⁺-channel opener pinacidil were similar in diabetics and controls, indicating intact endothelium-independent vasodilator mechanisms. The contribution of endothelium-derived hyperpolarizing factor to vasodilation induced by acetylcholine was greatest in the smallest arterioles. In diabetic rats, the response to acetylcholine was increasingly impared as vessel size decreased. Defective vasodilation in diabetic kidneys was rapidly normalized by 5-methyltetrahydrofolate. Conclusion-interpretation. Endothelium-derived hyperpolarizing factor-mediated vasodilation is impaired in the renal microcirculation of diabetic rats, in particular in the smallest arteries. Treatment with folate restores the impaired endothelial function in diabetes. [Diabetologia (2000) 43: 1116–1125] Received: 27 March 2000 and in revised from: 29 May 2000     

Pycnogenol, French maritime pine bark extract, augments endothelium-dependent vasodilation in humans.

Pycnogenol, an extract of bark from the French maritime pine, Pinus pinaster Ait., consists of a concentrate of water-soluble polyphenols. Pycnogenol contains the bioflavonoids catechin and taxifolin as well as phenolcarbonic acids. Antioxidants, such as bioflavonoids, enhance endothelial nitric oxide (NO) synthase expression and subsequent NO release from endothelial cells. The purpose of this study was to determine Pycnogenol's effects on endothelium-dependent vasodilation in humans. This was a double-blind, randomized, placebo and active drug study. We evaluated forearm blood flow (FBF) responses to acetylcholine (ACh), an endothelium-dependent vasodilator, and to sodium nitroprusside (SNP), an endothelium-independent vasodilator, in healthy young men before and after 2 weeks of daily oral administration of Pycnogenol (180 mg/day) (n=8) or placebo (n=8). FBF was measured by using strain-gauge plethysmography. Neither the placebo nor Pycnogenol altered forearm or systemic hemodynamics. Pycnogenol, but not placebo, augmented FBF response to ACh, from 13.1 +/- 7.0 to 18.5 +/- 4.0 mL/min per 100 mL tissue (p<0.05). SNP-stimulated vasodilation was similar before and after 2 weeks of treatment in the control and Pycnogenol groups. The administration of N(G)-monomethyl-L-arginine, an NO synthase inhibitor, completely abolished Pycnogenol-induced augmentation of the FBF response to ACh. These findings suggest that Pycnogenol augments endothelium-dependent vasodilation by increasing in NO production. Pycnogenol would be useful for treating various diseases whose pathogeneses involve endothelial dysfunction.     

Aging-Associated Endothelial Dysfunction in Humans Is Reversed by

Aldosterone has rapid nongenomic effects in the human vasculature. However, data are not uniform and little is known about chronic effects of aldosterone. Therefore, we investigated acute and chronic effects of elevated aldosterone levels on endothelial function in the forearm vasculature of healthy men. In a first crossover study, the effects of arterial aldosterone infusion in ascending doses (3.3 to 55 pmol/min per 1000 mL forearm volume) on forearm blood flow were investigated in 8 healthy men (26+/-2 years). In a second study, endothelium-dependent (acetylcholine; 0.08, 0.275, and 2.75 micromol/min per 1000 mL) and endothelium-independent (sodium nitroprusside 0.02 micromol/min per 1000 mL) vasodilation and basal nitric oxide formation (forearm blood flow response to blockade by N(G)-monomethyl-l-arginine 8 micromol/min per 1000 mL) were tested in 10 healthy men (age 30+/-5 years) at baseline, during infusion of 55 pmol/1000 mL per min aldosterone (acute effects), and after 0.3 mg/d oral fludrocortisone for 2 weeks (chronic effects) on separate days. Forearm blood flow was assessed by venous occlusion plethysmography. No change in forearm blood flow was seen with aldosterone infusion alone. Acute coinfusion of aldosterone increased vasodilation to sodium nitroprusside by 93% (P<0.01) and to acetylcholine by 60% (P=0.14). Response to N(G)-monomethyl-l-arginine did not change. After 2 weeks of oral fludrocortisone, response to acetylcholine was enhanced by 72% compared with baseline (P=0.03). Additionally, response to N(G)-monomethyl-l-arginine was enhanced by 80% compared with baseline (P=0.05). Aldosterone acutely enhances vasodilation to exogenous nitric oxide whereas mineralocorticoid excess for 2 weeks enhances basal nitric oxide bioactivity and improves endothelium dependent, nitric oxide-mediated vasodilation in the forearm vasculature of healthy men.     

Influence of acute and chronic mineralocorticoid excess on endothelial function in healthy men

Aldosterone has rapid nongenomic effects in the human vasculature. However, data are not uniform and little is known about chronic effects of aldosterone. Therefore, we investigated acute and chronic effects of elevated aldosterone levels on endothelial function in the forearm vasculature of healthy men. In a first crossover study, the effects of arterial aldosterone infusion in ascending doses (3.3 to 55 pmol/min per 1000 mL forearm volume) on forearm blood flow were investigated in 8 healthy men (26+/-2 years). In a second study, endothelium-dependent (acetylcholine; 0.08, 0.275, and 2.75 micromol/min per 1000 mL) and endothelium-independent (sodium nitroprusside 0.02 micromol/min per 1000 mL) vasodilation and basal nitric oxide formation (forearm blood flow response to blockade by N(G)-monomethyl-l-arginine 8 micromol/min per 1000 mL) were tested in 10 healthy men (age 30+/-5 years) at baseline, during infusion of 55 pmol/1000 mL per min aldosterone (acute effects), and after 0.3 mg/d oral fludrocortisone for 2 weeks (chronic effects) on separate days. Forearm blood flow was assessed by venous occlusion plethysmography. No change in forearm blood flow was seen with aldosterone infusion alone. Acute coinfusion of aldosterone increased vasodilation to sodium nitroprusside by 93% (P<0.01) and to acetylcholine by 60% (P=0.14). Response to N(G)-monomethyl-l-arginine did not change. After 2 weeks of oral fludrocortisone, response to acetylcholine was enhanced by 72% compared with baseline (P=0.03). Additionally, response to N(G)-monomethyl-l-arginine was enhanced by 80% compared with baseline (P=0.05). Aldosterone acutely enhances vasodilation to exogenous nitric oxide whereas mineralocorticoid excess for 2 weeks enhances basal nitric oxide bioactivity and improves endothelium dependent, nitric oxide-mediated vasodilation in the forearm vasculature of healthy men.     

Oral L-arginine supplementation and cutaneous vascular responses in patients with primary Raynaud's phenomenon

Objective. To assess the effects of oral L-arginine supplementation on cutaneous vascular responses in patients with primary Raynaud's phenomenon (RP). Methods. Double-blind, crossover comparison of placebo versus L-arginine (8 gm/day for 28 days). Cutaneous vascular responses in the fingers were assessed during iontophoresis of acetylcholine and sodium nitroprusside, which are endothelium-dependent and endothelium-independent vasodilators. Results. In comparison with control subjects, patients with primary RP had diminished endothelium-dependent and -independent vasodilatation (P < 0.05, and P < 0.005, respectively, by analysis of variance). At the 3 doses used, vascular responses to acetylcholine were reduced by 71%, 64%, and 63%, respectively, and responses to sodium nitroprusside were reduced by 67%, 73%, and 66%, respectively. L-arginine had no significant effect on cutaneous vascular responses to acetylcholine or sodium nitroprusside in control subjects or patients with primary RP. Conclusion. Reduced vasodilator ability in primary RP is unlikely to be due to an impairment in the L-arginine/nitric oxide pathway.     

Acute effects of glucose and insulin on vascular endothelium

Aims/hypothesis Chronic exposure to high concentrations of glucose has consistently been demonstrated to impair endothelium-dependent, nitric oxide (NO)-mediated vasodilation. In contrast, several clinical investigations have reported that acute exposure to high glucose, alone or in combination with insulin, triggers vasodilation. The aim of this study was to examine whether elevated glucose itself stimulates endothelial NO formation or enhances insulin-mediated endothelial NO release.Methods We measured NO release and vessel tone ex vivo in porcine coronary conduit arteries (PCAs). Intracellular Ca²⁺ was monitored in porcine aortic endothelial cells (PAECs) by fura-2 fluorescence. Expression of the Na⁺/glucose cotransporter-1 (SGLT-1) was assayed in PAECs and PCA endothelium by RT-PCR.Results Stimulation of PCAs with d-glucose, but not the osmotic control l-glucose, induced a transient increase in NO release (EC₅₀10 mmol/l), mediated by a rise in intracellular Ca²⁺ levels due to an influx from the extracellular space. This effect was abolished by inhibitors of the plasmalemmal Na⁺/Ca²⁺ exchanger (dichlorobenzamil) and the SGLT-1 (phlorizin), which was found to be expressed in aortic and coronary endothelium. Alone, d-glucose did not relax PCA, but did augment the effect of insulin on NO release and vasodilation.Conclusions/interpretation An increased supply of extracellular d-glucose appears to enhance the activity of the endothelial isoform of nitric oxide synthase by increasing intracellular Na⁺ concentrations via SGLT-1, which in turn stimulates an extracellular Ca²⁺ influx through the Na⁺/Ca²⁺ exchanger. This mechanism may be responsible for glucose-enhanced, insulin-dependent increases in tissue perfusion (including coronary blood-flow), thus accelerating glucose extraction from the blood circulation to limit the adverse vascular effects of prolonged hyperglycaemia.     

Evidence of partially preserved endothelial dilator function in diseased coronary arteries

OBJECTIVE—To examine the effects of substance P (endothelium dependent vasodilator) and glyceryl trinitrate (endothelium independent vasodilator) on epicardial coronary arteries in patients with normal coronary angiograms and patients with coronary artery disease.
DESIGN—Intracoronary infusions of normal saline, the receptor mediated nitric oxide stimulant substance P (5.6 and 27.8 pmol/min each for five minutes), and glyceryl trinitrate (250 µg bolus) were given in 24 patients with coronary artery disease and stable angina, and in nine patients with normal angiograms. The diameter of proximal and distal coronary segments was measured by computerised quantitative angiography
RESULTS—Proximal segments of patients with coronary artery disease dilated less than those of patients with normal angiograms in response to 27.8 pmol/min substance P (mean (SEM): 7.9 (1.3)% v 15 (2.3)% respectively, p < 0.01). The proximal segments of diseased arteries also dilated less than those of "normal" arteries in response to glyceryl trinitrate (10.2 (1.6)% v 18.4 (2.9)%, respectively, p < 0.01). The responses of distal segments to substance P and glyceryl trinitrate were similar in the two patient groups. There were correlations (all p < 0.001) between the coronary diameter after substance P and after glyceryl trinitrate in normal proximal segments (r = 0.94) and normal distal segments (r = 0.64), in diseased proximal segments (r = 0.95) and diseased distal segments (r = 0.89), and for coronary stenoses (r = 0.93).
CONCLUSIONS—Proximal segments of patients with coronary disease dilated less than the proximal segments of "normal" patients in response to substance P and glyceryl trinitrate. The response to substance P is substantial and closely correlated with the response to glyceryl trinitrate in both "normal" patients and those with coronary disease. This suggests that although the proximal segments of diseased coronary arteries have a reduced capacity to dilate in response to direct stimulation of smooth muscle cell relaxation, they retain much of their endothelium dependent vasodilator function.


Keywords: endothelium; nitric oxide; coronary artery disease; glyceryl trinitrate     

Pathogenetic Factors in Hypertension Endothelial Factors

In normotensive humans, endothelium modulates vascular tone mainly by the production of nitric oxide. In human essential hypertension the basal release of nitric oxide is reduced and forearm vasodilation to the endothelium-dependent agonists acetylcholine or bradykinin is blunted. Defective basal release of nitric oxide seems to be secondary to blood pressure increase while impaired agonist-evoked endothelium-dependent vasodilation is probably a primary phenomenum. This latter endothelial dysfunction seems to be caused by the simultaneous presence of an alteration in the L-arginine-nitric oxide pathway and the production of constrictor prostanoids. Defective nitric oxide production is already detectable in normotensive offspring of hypertensive patients and young essential hypertensives. In contrast, vasoconstrictor prostanoid production seems to be associated with aging.In essential hypertensive patients, although only scanty data are available, chronic effective pharmacological treatment seems to restore impaired basal production of nitric oxide but does not improve vascular response to endothelial agonists.