Endothelin-1 inhibits endothelium-dependent vasodilatation in the human forearm: reversal by ETA receptor blockade in patients with atherosclerosis

Several cardiovascular disorders, including atherosclerosis, are associated with endothelial dysfunction and enhanced expression of endothelin-1 (ET-1). The role of ET-1 in the development of endothelial dysfunction in vivo remains unclear. The objective of the present study was to investigate the effect of elevated circulating levels of ET-1 on endothelium-dependent vasodilatation (EDV), and to test the hypothesis that ET(A) receptor antagonism improves EDV in patients with atherosclerosis. EDV and endothelium-independent vasodilatation were determined by brachial artery infusion of acetylcholine and sodium nitroprusside respectively during measurement of forearm blood flow (FBF) with venous occlusion plethysmography. A 60 min intra-arterial infusion of ET-1 (n=10) significantly blunted EDV in young healthy males (33 +/- 13% compared with 271 +/- 74% increase in FBF induced by 10 mug/min acetylcholine; P<0.01). Noradrenaline, which evoked a similar degree of vasoconstriction, did not attenuate EDV. In a separate set of experiments, a 60 min intra-arterial infusion of the selective ET(A) receptor antagonist BQ123 evoked a significant increase in EDV in patients with atherosclerosis (n=10; 109 +/- 45% compared with 255 +/- 101% increase in FBF induced by 10 microg/min acetylcholine; P<0.01), whereas no significant change was observed in healthy age-matched controls (n=9). Endothelium-independent vasodilatation was not affected by ET-1 or BQ123. These observations demonstrate that elevated levels of ET-1 impair EDV in healthy control subjects. Furthermore, ET(A) receptor blockade improves EDV in patients with atherosclerosis, indicating that ET-1 attenuates EDV via an ET(A)-receptor-mediated mechanism.     

The impairment in endothelial function induced by non-esterified fatty acids can be reversed by insulin

Dyslipidaemia, with elevations of circulating triacylglycerols (triglycerides) and non-esterified (free) fatty acids, and hyperinsulinaemia are often found in the same subjects, the so-called 'insulin resistance syndrome'. The present study aims to investigate how elevated levels of non-esterified fatty acids, hyperinsulinaemia and the combination of these factors affects endothelium-dependent vasodilatation (EDV). Ten volunteers were examined on two occasions. Intralipid (plus heparin) or saline (0.9% NaCl) was infused for 4 h. During the final 2 h, euglycaemic hyperinsulinaemia (80+/-4 m-units/l) was imposed. EDV and endothelium-independent vasodilatation were evaluated in the forearm by local intra-arterial infusion of methacholine or sodium nitroprusside at baseline and after 2 and 4 h. Forearm blood flow was measured by venous occlusion plethysmography. Lipid oxidation was determined by measuring plasma malondialdehyde levels. Infusion of Intralipid plus heparin increased the concentration of non-esterified fatty acids to 2.6+/-1.2 mmol/l and decreased EDV from 27.6+/-8.7 to 21.0+/-5.7 ml x min(-1) x 100 ml(-1) tissue (P < 0.01). This effect was completely reversed by hyperinsulinaemia (P < 0.01). Hyperinsulinaemia alone increased EDV (to 30.4+/-9.5 ml x min(-1) x 100 ml(-1) tissue; P < 0.01), while endothelium-independent vasodilatation was unaltered by the interventions. Infusion of Intralipid plus heparin increased malondialdehyde levels from 0.67+/-0.22 to 1.2+/-0.37 micromol/l (P < 0.001), while hyperinsulinaemiadid not change the malondialdehyde level. In conclusion, an acute increase in serum levels of non-esterified fatty acids increased lipid oxidation and decreased EDV. The effect on EDV of non-esterified fatty acids could be reversed by hyperinsulinaemia.     

Endothelin-1 vasoconstriction and the age-related decline in endothelium-dependent vasodilatation in men

ET (endothelin)-1, a potent vasoconstrictor peptide released by the endothelium, plays an important role in vasomotor regulation and has been linked to diminished endothelial vasodilator capacity in several pathologies associated with human aging, including hypertension, Type 2 diabetes and coronary artery disease. However, it is currently unknown whether the decline in endothelial vasodilatation with advancing age is due to elevated ET-1 vasoconstrictor activity. Accordingly, we tested the hypothesis that the age-related impairment in ACh (acetylcholine)-mediated endothelium-dependent vasodilatation is due, at least in part, to increased ET-1-mediated vasoconstrictor tone. FBF (forearm blood flow) responses to ACh, SNP (sodium nitroprusside) and BQ-123 (ET(A) receptor blocker) were determined in 14 young (age, 25 ± 1 years) and 14 older (age, 61 ± 2 years) healthy non-obese men. Additionally, FBF responses to ACh were determined in the presence of ETA blockade. Vasodilatation to ACh was lower (approx. 25%; P<0.05) in the older men (from 4.9 ± 0.2 to 13.9 ± 0.9 ml·100 ml(-1) of tissue·min(-1)) compared with the young men (4.6 ± 0.3 to 17.2 ± 1.0 ml·100 ml(-1) of tissue·min(-1)). There were no differences in FBF responses to SNP between the young (4.8 ± 0.3 to 18.5 ± 0.3 ml·100 ml(-1) of tissue·min(-1)) and older (5.1 ± 0.3 to 17.3 ± 0.8 ml·100 ml(-1) of tissue·min(-1)) men. In the young men, resting FBF was not significantly altered by BQ-123, whereas, in the older men, FBF increased approx. 25% in response to BQ-123 infusion (P<0.05). Co-infusion of ACh with BQ-123 resulted in an approx. 20% increase in the ACh-induced vasodilatation in older men compared with saline. In contrast, FBF responses to ACh were not significantly altered by ET(A) blockade in the young men. In conclusion, these results demonstrate that ET-1 vasoconstrictor activity contributes, at least in part, to diminished endothelium-dependent vasodilatation in older men.     

The endothelin-1 receptor antagonist bosentan protects against ischaemia/reperfusion-induced endothelial dysfunction in humans

Endothelial dysfunction may contribute to the extent of ischaemia/reperfusion injury. ET (endothelin)-1 receptor antagonism protects against myocardial ischaemia/reperfusion injury in animal models. The present study investigated whether oral administration of an ET(A)/ET(B) receptor antagonist protects against ischaemia/reperfusion-induced endothelial dysfunction in humans. FBF (forearm blood flow) was measured with venous occlusion plethysmography in 13 healthy male subjects. Forearm ischaemia was induced for 20 min followed by 60 min of reperfusion. Using a cross-over protocol, the subjects were randomized to oral administration of 500 mg of bosentan or placebo 2 h before ischaemia. Endothelium-dependent and -independent vasodilatation were determined by intra-brachial infusion of acetylcholine (1-10 microg/min) and nitroprusside (0.3-3 microg/min) respectively, before and after ischaemia. Compared with pre-ischaemia, the endothelium-dependent increase in FBF was significantly impaired at 15 and 30 min of reperfusion when the subjects received placebo (P<0.01). When the subjects received bosentan, the endothelium-dependent increase in FBF was not affected by ischaemia/reperfusion. Endothelium-independent vasodilatation was not affected during reperfusion compared with pre-ischaemia. The vaso-constrictor response induced by intra-arterial infusion of ET-1 was attenuated significantly by bosentan (P<0.001). The results suggest that the dual ET(A)/ET(B) receptor antagonist bosentan attenuates ischaemia/reperfusion-induced endothelial dysfunction in humans in vivo. Bosentan may thus be a feasible therapeutic agent in the treatment of ischaemia/reperfusion injury in humans.     

Methodological aspects of the evaluation of endothelium-dependent vasodilatation in the human forearm

The present study, involving 56 healthy subjects from a health screening, was undertaken to address some methodological questions regarding the measurement of endothelial function using local intra-arterial infusions of metacholine (2 and 5 μg min^?1) to evaluate endothelium-dependent vasodilatation, and sodium nitroprusside (SNP, 5 and 10 μg min^?1) to evaluate endothelium-independent vasodilatation. Forearm blood flow (FBF) was measured by venous occlusion plethysmography. The ratio of FBF during the highest dose of metacholine to FBF during the highest dose of SNP was used as an index of endothelial function. In 10 young volunteers the procedure was repeated after 2 h and again after 3 weeks in order to study short-term and long-term reproducibility of the method. Neither the vasodilatatory response to metacholine (r = 0·006) nor that to SNP (r = 0·08) was related to resting FBF. Neither the circumference nor the length of the arm was related to endothelial function (r = 0·01?0·11), as evaluated by the FBF on metacholine to nitroprusside ratio (mean 1·3 ± 0·3 SD). The use of a wrist cuff to exclude hand circulation, or not, did not influence the evaluation of endothelial function significantly. Maximal FBF after 3 min of arterial occlusion of the forearm was significantly related to blood flow during both metacholine (r = 0·53, P < 0·01) and nitroprusside infusion (r = 0·36, P < 0·05), but not to the FBF on metacholine to nitroprusside ratio (r = 0·01). The short-term and long-term reproducibility of FBF during vasodilatation with metacholine and SNP was good (r = 0·89?0·97, P < 0·001), while the individual measurements for resting FBF were less reproducible when repeated after 3 weeks (r = 0·34). In conclusion, endothelial function was not related to resting FBF, nor to the arm circumference or length. No major difference was seen whether endothelial function was evaluated with or without exclusion of the hand circulation. Maximal FBF during reactive hyperaemia was not related to endothelial function.     

Forearm vasoconstriction in response to noradrenaline and NG-monomethyl-L-arginine in essential hypertension.

A role for abnormal NO production in essential hypertension remains controversial. Blunted vasoconstriction of forearm resistance vasculature in response to N(G)-monomethyl-L-arginine (L-NMMA; an inhibitor of NO biosynthesis), relative to the response to noradrenaline, has been reported in hypertensive patients and interpreted as evidence of reduced basal NO biosynthesis. We sought to determine whether reduced sensitivity of forearm vasculature to the vasoconstrictor action of L-NMMA relative to that of noradrenaline is a consistent finding in essential hypertension. We studied a group of patients (n=32; blood pressure 176+/-4/102+/-2 mmHg; means+/-S.E.M.) and a group of healthy normotensive controls (n=32; blood pressure 130+/-2/75+/-1 mmHg). Noradrenaline (60-240 pmol.min(-1)) and L-NMMA (1-4 micromol.min(-1)) were infused into the brachial artery, and forearm blood flow was measured by venous occlusion plethysmography. The effects of each vasoconstrictor were similar in hypertensive and control subjects. The highest dose of L-NMMA reduced forearm blood flow by 0.75+/-0.12 ml.min(-1).dl(-1) in the control group and by 0.89+/-0.10 ml.min(-1).dl(-1) in the hypertensive group. The study had 90% power (with P=0.05) to detect a 10% difference in forearm blood flow response between the hypertensive and control groups. We conclude that reduced sensitivity of forearm resistance vasculature to the vasoconstrictor action of L-NMMA is not a universal feature of essential hypertension. This argues against a primary role for reduced basal NO biosynthesis in skeletal muscle resistance vessels in the pathogenesis of essential hypertension.     

Effect of glycyrrhetinic acid on 11 beta-hydroxysteroid dehydrogenase activity in normotensive and hypertensive subjects

The 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) isoenzymes catalyse the interconversion of cortisol and cortisone. Type 1 11 beta-HSD mainly converts cortisone into active cortisol. Type 2 11 beta-HSD inactivates cortisol in mineralocorticoid target tissues, and its activity can be inhibited by glycyrrhetinic acid (GA). Inactivation of cortisol to cortisone is impaired in a subgroup of patients with primary hypertension. To study where this defect is located, we measured cortisol and cortisone concentrations in arterial plasma, in saliva and across the forearm at baseline and after administration of GA in normotensive and hypertensive subjects. GA (500 mg) or placebo was administered orally to 20 normotensive subjects in a placebo-controlled double-blind fashion. Further, we compared the effect of GA in 20 patients with primary hypertension with that in 20 normotensive subjects. Cortisol and cortisone were measured in plasma from the brachial artery and vein and in saliva. Samples were obtained at 0, 90 and 150 min. Forearm blood flow (FBF) was measured simultaneously. Forearm production of corticosteroid hormones was assessed by multiplying the arteriovenous difference in corticosteroid concentration by FBF. The cortisol/cortisone ratio in arterial plasma remained at baseline levels after placebo (4.9 +/- 1.2; mean +/- S.D.), while after GA the ratio increased similarly in normotensive subjects (12.3 +/- 3.4) and in hypertensive patients (12.2 +/- 3.7). A similar effect of GA on the salivary cortisol/cortisone ratio was found. In both normotensive subjects and hypertensive patients no forearm production of cortisol or cortisone could be demonstrated, either at baseline or after administration of GA. Thus, both before and after GA administration, we did not find any difference in systemic and salivary 11 beta-HSD type 2 activity between subjects with primary hypertension and normotensive controls. Further, both at baseline and after GA administration we were not able to demonstrate net inactivation or re-activation of cortisol and cortisone by the 11 beta-HSD isoenzymes in the forearm in either normotensive or primary hypertensive subjects.     

Biphasic forearm vascular responses to intraarterial arginine vasopressin.

Forearm vascular responses to arginine vasopressin (AVP) infused into a brachial artery in a wide range of infusion rates (0.05-2.0 ng/kg per min) were examined in 20 young healthy volunteers. Intraarterial AVP at lower doses (0.05 and 0.1 ng/kg per min) caused forearm vasoconstriction, whereas AVP at a dose of 0.2 ng/kg per min or higher caused forearm vasodilatation. The maximal forearm vasoconstriction was induced at the venous plasma AVP level of 76.3 +/- 8.8 pg/ml. Forearm vasodilatation was associated with the venous plasma AVP level of 369 +/- 43 pg/ml or higher. Forearm vasodilatation was the result of the direct effect of AVP since forearm blood flow and vascular resistance in the contralateral arm did not change. We attempted to explore the mechanisms involved in AVP-induced direct vasodilatation. The treatment with indomethacin, 75 mg/d for 3 d, did not alter AVP-induced forearm vasodilatation. In contrast, intraarterial infusion of isoosmolar CaCl2 totally prevented AVP-induced forearm vasodilatation. Intra-arterial CaCl2 also markedly attenuated forearm vasodilatation induced by intraarterial sodium nitroprusside, but did not alter forearm vasodilatation induced by intraarterial isoproterenol. These results indicate that the direct vascular effects of intra-arterial AVP on the forearm vessels are biphasic, causing vasoconstriction at lower doses and vasodilatation at higher doses. The direct vasodilatation induced by intraarterial AVP at higher doses is not mediated by prostaglandins but may involve cGMP-related mechanisms.     

Basal nitric oxide production is impaired in offspring of patients with essential hypertension.

There is considerable evidence that endothelium-dependent nitric oxide (NO)-mediated vasodilatation in response to acetylcholine is impaired in essential hypertension, whereas the endothelium-independent response to sodium nitroprusside is normal. More limited data have suggested that there is also reduced vasoconstriction in response to N(G)-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of basal NO release. As it is not known whether endothelial dysfunction in hypertension, if indeed present, is a cause or consequence of the condition, we have studied the normotensive offspring of parents with essential hypertension. Both basal and stimulated vascular responses were examined in 12 normotensive offspring [mean age (+/-S.E.M.) 26.1+/-1.4 years] of parents with essential hypertension and compared with those in 12 age-matched offspring (mean age 25.6+/-1.1 years) of normotensive subjects. Forearm blood flow was measured simultaneously in both arms by venous occlusion plethysmography, both at baseline and during intra-arterial brachial infusion of increasing doses of acetylcholine, sodium nitroprusside, noradrenaline and L-NMMA. There were no significant differences between the groups in the responses to acetylcholine, sodium nitroprusside or noradrenaline. In contrast, the vasoconstrictor response to L-NMMA was significantly blunted in the offspring of hypertensive parents compared with that in the offspring of normotensive parents (P=0.005). Thus endothelial dysfunction, as demonstrated by impaired basal production of NO, is present in subjects at high risk of essential hypertension, and does not occur simply as a consequence of the condition.     

Activation of the ATP-dependent potassium channel attenuates norepinephrine-induced vasoconstriction in the human forearm

Sepsis-induced vasodilation is characterized by an attenuated sensitivity to vasoconstrictor substances such as norepinephrine, possibly mediated by activation of vascular potassium channels. We determined whether vasodilation associated with potassium channel activation resulted in an attenuated vasoconstrictive response to norepinephrine in humans and whether the vasodilation associated with potassium channel activation could be inhibited by pharmacological potassium channel blockers. In 30 volunteers, the brachial artery was cannulated for infusion of drugs. Forearm blood flow (FBF) was measured in both arms using strain-gauge venous occlusion plethysmography. Forearm vascular resistance (FVR, mean arterial pressure/FBF) was calculated. The effects of vasodilation induced by sodium nitroprusside (SNP, nitric oxide donor) or diazoxide (activator of the ATP-dependent potassium channel) on norepinephrine-mediated vasoconstriction were examined. Also, the effects of potassium channel blockers on vasodilation associated with potassium channel activation were determined. Intraarterial SNP infusion (2 microg/min/dL) increased forearm blood flow by 235%, from (mean +/- SEM) 2.8 +/- 0.7 to 9.4 +/- 1.5 mL/min/dL (P < 0.0001). Subsequent norepinephrine infusion (10, 30, 100, 300, 1000 ng/min/dL) increased FVR dose-dependently from 13 +/- 4 AU to 249 +/- 45 AU at the highest norepinephrine infusion. Intraarterial diazoxide infusion (1 mg/min/dL) increased FBF by 209% from 2.2 +/- 0.3 to 6.8 +/- 1.0 mL/min/dL (P < 0.001). Subsequent norepinephrine infusion increased FVR from 18 +/- 5 to 51 +/- 6 AU at the highest norepinephrine infusion rate (n = 10), significantly different from the norepinephrine-induced effects during SNP coinfusion (P < 0.001). Diazoxide-induced fall in FVR in the infused forearm was inhibited by potassium channel blockers tetraethyl ammonium (1 mg/min/dL, n = 10, P = 0.004) and quinine (50 microg/min/dL, n = 10, P = 0.016). Vasodilation induced by vascular potassium channel activation is associated with an impressive reduction in the vasoconstrictor response to norepinephrine in humans. In accordance with animal experiments, this indicates that potassium channel activation could account for the diminished norepinephrine sensitivity in septic patients. Vasodilation associated with potassium channel activation can be inhibited by pharmacological potassium channel blockade. The possible role of potassium channel blockers during sepsis-induced potassium channel activation and vasodilation in humans needs further elucidation.     

Effects of tumour necrosis factor-alpha in the human forearm: blood flow and endothelin-1 release

Increased circulating concentrations of tumour necrosis factor-alpha (TNF-alpha) are seen in several pathological conditions associated with vascular disease. TNF-alpha induces the synthesis of endothelin-1 (ET-1), a potent vasoconstictor, by the endothelium. However, there is profound vasodilatation in sepsis, where circulating levels of both ET-1 and TNF-alpha are elevated. The details of the interaction between ET-1 and TNF-alpha and the predominant resulting haemodynamic effect in healthy humans are unclear. The aim of the present study was to determine the effects of intra-arterial TNF-alpha on ET-1 spillover, vascular tone and endothelial function in the healthy human forearm. Brachial arterial and deep venous blood samples, forearm plasma flow measurements and blood flow responses to acetylcholine and sodium nitroprusside were obtained in six healthy subjects before and during a 6 h infusion of TNF-alpha into the brachial artery. Forearm blood flow was significantly greater than baseline during exposure to TNF-alpha [median (lower quartile, upper quartile): baseline, 2.6 (2.1, 2.8) ml.min(-1).100 ml(-1); TNF-alpha, 4.6 (4.5, 5.1) ml.min(-1).100 ml(-1); P <0.05]. The rate of release of ET-1 was significantly greater than baseline after 30 and 260 min of TNF-alpha infusion [median (lower quartile, upper quartile): baseline, 0.8 (0.6, 1.1) pg.min(-1).100 ml(-1); 30 min, 2.4 (1.9, 3.2) pg.min(-1).100 ml(-1); 260 min, 4.1 (3.1, 4.2) pg.min(-1).100 ml(-1); P <0.05]. The vasodilatory response to acetylcholine was diminished during TNF-alpha infusion, whereas the response to sodium nitroprusside remained unchanged. We thus demonstrate for the first time that local TNF-alpha increases ET-1 spillover from the human forearm and impairs endothelium-dependent vasodilatation. In spite of this action, TNF-alpha has a vasodilatory effect, resulting in an increase in forearm blood flow.     

Intra-arterial vasodilator agents to reverse human finger vasoconstriction

Persistent vasospasm of the digits is difficult to attenuate or reverse. We studied the effect of intra-arterial nitroprusside on humoral and neurogenic digital vasoconstriction. Fingertip blood flow (FBF) was measured by venous occlusion plethysmography and capillary flow (CF) by the disappearance rate of a local injection of radioisotope. Small doses of nitroprusside (1 to 2 micrograms/min) increased FBF in fingers vasoconstricted by intra-arterial norepinephrine (4.7 +/- SE 1.7 to 38.4 +/- 26 ml min-1 100 ml-1 of tissue). Large doses of nitroprusside (up to 40 micrograms/min) did not increase FBF (11.8 +/- 6.0 ml to 6.6 +/- 3.9 ml) in fingers vasoconstricted by sympathetic nerve stimulation (body cooling). Forearm blood flow was measured in six subjects in the cool room and all showed an increase in flow with nitroprusside (6.7 +/- 1.1 ml to 26.0 +/- 6.0 ml), demonstrating that effective doses were used. Nitroglycerin (2.5 to 5 micrograms/min) significantly increased FBF from 5.1 +/- 1.9 ml to 14.8 +/- 6.9 ml as did phentolamine (50 to 100 micrograms/min) from 6.7 +/- 2.8 ml to 36.0 +/- 11.3 ml in sympathetically vasoconstricted subjects. Only phentolamine increased CF significantly (0.8 +/- 0.2 ml to 2.8 +/- 0.6 ml). Nitroprusside is an effective vasodilator for humorally induced vasoconstriction, but sympathetic digital vasoconstriction is resistant to nitroprusside and nitroglycerin is less effective than phentolamine. Phentolamine is the preferred agent because it increased FBF and CF.     

Basal and exercise-induced skeletal muscle blood flow is augmented in type I diabetes mellitus

Hyperaemia occurs early in the renal and retinal microcirculation of patients with type I (insulin-dependent) diabetes mellitus, and may be critical in the development of nephropathy and retinopathy. We therefore sought to determine whether resting and exercise-induced hyperaemia was also apparent in the skeletal muscle circulation of young subjects with type I diabetes. Blood flow was assessed by venous occlusion plethysmography in 18 diabetic (DM) subjects and 20 matched controls. Exercise entailed 2 min of isotonic exercise against no load. Endothelium-dependent and -independent vasodilator function was assessed following intra-arterial infusion of acetylcholine and sodium nitroprusside respectively. Forearm blood flow (FBF) was higher in DM subjects than in controls (3.3+/-0.3 and 2.2+/-0.2 ml x min(-1) x 100 ml(-1) forearm respectively; P<0.005). This was not due to differences in forearm or body size, blood pressure, heart rate, lipid status or glycaemic control. Peripheral insulin levels were higher in DM subjects than in controls (48.5+/-8 and 15.5+/-1.5 micro-units/ml respectively; P<0.005). Resting FBF was closely correlated with insulin levels (r(2)=0.4; P<0.005). Parameters of exercise-induced hyperaemia [including peak flow (16.4+/-1.4 and 12.0+/-0.7 ml x min(-1) x 100 ml(-1) forearm in DM and control subjects respectively; P<0.01) and the volume repaid to the forearm at 5 min post-exercise (32.1+/-3.1 and 23.1+/-1.4 ml x 100 ml(-1) forearm respectively; P<0.05)] were also significantly greater in DM subjects, even when differences in resting FBF were taken into account. Peak hyperaemic blood flow and the volume repaid at 5 min were also related to insulin levels (r(2)=0.16; P<0.05 and r(2)=0.27; P<0.005 respectively). The vasodilator response to acetylcholine was reduced in DM subjects (P<0.05; analysis of variance), and the slope of this dose-flow relationship was inversely related to insulin levels (r(2)=0.2; P<0.05). These data show that both resting and exercise-induced skeletal muscle blood flow are augmented in young patients with type I diabetes, possibly due to the vasodilatory effect of increased insulin levels. Diminished vasodilator responses to acetylcholine may also, in part, be a consequence of insulin-augmented resting muscle blood flow.     

Forearm vascular response to nitric oxide and calcitonin gene-related peptide: comparison between migraine patients and control subjects

The forearm vascular response to nitric oxide (NO) and calcitonin gene-related peptide (CGRP) was investigated in 10 migraine patients and 10 matched control subjects. Changes in forearm blood flow (FBF) during intrabrachial infusion of: (i) serotonin (releasing endogenous NO), (ii) sodium nitroprusside (SNP, exogenous NO-donor), and (iii) CGRP were measured using venous occlusion plethysmography. Flow-mediated dilation (FMD) of the brachial artery, a measure for the endogenous release of NO reactive to occlusion, was measured using ultrasound and expressed as percentage change vs. baseline diameter. FBF ratio (i.e. FBF in the infused over the control arm) at baseline (1.1 +/- 0.1) did not differ between both populations. Serotonin, SNP and CGRP induced a dose-dependent increase (P < 0.001) in FBF ratio in controls (to 2.8 +/- 0.3, 6.7 +/- 1.4 and 6.9 +/- 1.2 at the highest dose, respectively) and migraineurs (2.5 +/- 0.4, 5.6 +/- 0.8 and 6.5 +/- 1.3, respectively); these ratios did not differ between both groups. FMD was comparable in control subjects (5.8 +/- 1%) and migraine patients (5.2 +/- 1%). Based on the forearm vascular response to NO and CGRP, migraine patients do not display generalized changes in vascular function.     

Endothelium-dependent vasodilation and structural and functional changes in the cardiovascular system are dependent on age in healthy subjects

The aim of this study was to evaluate possible associations between endothelium-dependent vasodilatation (EDV) and cardiovascular structure and function. EDV could influence peripheral resistance and be affected by atherosclerosis and might thereby influence indices of cardiovascular structure and function. In a group of 31 apparently healthy men and 25 women (age range 20–69 years), EDV was evaluated by infusion of metacholine (4 μg min^–1), and endothelium-independent vasodilatation (EIDV) was assessed by nitroprusside infusion (SNP, 10 μg min^–1) in the brachial artery. Forearm blood flow (FBF) was measured by venous occlusion plethysmography. Left ventricular (LV) geometry and function and the intima-media thickness in the carotid artery were assessed by ultrasonography. The stroke index to pulse pressure ratio was used to evaluate arterial compliance. Several indices of cardiovascular structure and function were found to be related to an index of endothelial function, the EDV to EIDV ratio. Furthermore, left ventricular mass (LVM), the atrio-ventricular plane displacement, E/A ratio, IVRT, the intima-media thickness of the carotid artery and arterial compliance were all significantly related to both EDV and EIDV in women. However, most indices of cardiovascular structure and function, as well as endothelial function, change with age and only the relation between LV diastolic function and endothelial function in men remained significant (P<0·05) after including age in multiple regression analysis. Age was related to both cardiovascular structure and function, as well as to endothelial function. Multiple regression analysis showed that ageing generally affects cardiovascular characteristics and endothelial function in parallel in these healthy subjects.     

Local forearm vasodilation with intra-arterial administration of enalaprilat in humans.

To determine whether converting enzyme inhibitors could produce peripheral vasodilation through a local mechanism, we infused enalaprilat, 2 micrograms/min/dl forearm volume (FAV), into the brachial artery of normal subjects and measured changes in forearm blood flow (FBF) with strain-gauge plethysmography. Enalaprilat produced a peak increase in FBF of 2.82 +/- 0.54 ml/min/dl FAV (78% increase) at 1 minute (p less than 0.01 versus vehicle) and an increase of 1.11 +/- 0.28 ml/min/dl FAV at 4 minutes (p less than 0.05 versus vehicle). Blood pressure and plasma renin activity measured at the completion of infusion did not change. Intravenous enalaprilat infusion at the same dose in seven additional normal subjects did not increase FBF. Pretreatment of seven subjects with 75 mg oral indomethacin attenuated the peak response to enalaprilat (4.13 +/- 1.52 versus 0.58 +/- 0.32 ml/min/dl; p less than 0.05). We conclude that intra-arterial enalaprilat produces an increase in FBF in normal subjects. This peripheral vasodilation is caused by a local effect independent of circulating renin-angiotensin system inhibition. This response is attenuated by indomethacin, suggesting that prostaglandins contribute to the vasodilator response.     

Ageing impairs insulin-mediated vasodilatation but not forearm glucose uptake

BACKGROUND: It is unclear if insulin-mediated vasodilatation is altered by ageing and if this affects insulin-mediated glucose uptake. MATERIAL AND METHODS: A 2-h euglycaemic hyperinsulinaemic clamp (56 mU m(-2) min(-1)) was performed in 10 healthy, nonobese elderly men (70-75 years) and 13 young men (23-28 years). Forearm blood flow (FBF) was measured by venous occlusion plethysmography and forearm glucose uptake was calculated by arterial and venous serum glucose determinations in the forearm. RESULTS: Insulin induced an increase in FBF in the younger men (from 3.9 +/- 1.1 SD to 5.9 +/- 2.2 mL min(-1) 100(-1)mL tissue, P < 0.001), but this insulin-mediated vasodilatation was completely blunted in the elderly subjects. Glucose extraction during the clamp was significantly higher in the elderly subjects (1.2 +/- 0.76 vs. 0.82 +/- 0.37 mmol L(-1) at 120 min, P < 0.01), resulting in a similar forearm glucose uptake in the two groups. On the other hand, whole-body glucose uptake was significantly decreased in the elderly subjects (5.3 +/- 1.8 vs. 8.0 +/- 1.1 mg kg(-1) min(-1), P < 0.001). CONCLUSION: The present study showed that the ability of insulin to induce vasodilatation is blunted in the forearm in healthy, nonobese elderly subjects. However, the elderly compensate for this impairment with an increased glucose extraction from arterial blood to maintain an unaltered forearm glucose uptake.     

Direct and sympathetically mediated venoconstriction in essential hypertension. Enhanced responses to endothelin-1.

Endothelin-1 is a potent endothelium-derived vasoconstrictor peptide. Although circulating concentrations are not increased in essential hypertension, enhanced sensitivity to endothelin-1 has been observed in animal models of hypertension. We investigated dorsal hand vein responses to local infusion of endothelin-1 and norepinephrine in 12 patients with essential hypertension who had never received treatment and in 12 age and sex matched normotensive control subjects. The maximal venoconstriction and the geometric mean of the dose of norepinephrine that caused 50% of maximal venoconstriction were similar in hypertensive (mean +/- SE; 80 +/- 4%; 31 +/- 8 pmol/min) and normotensive subjects (87 +/- 5%, 22 +/- 9 pmol/min). In contrast, mean venoconstriction to endothelin-1 was significantly greater in hypertensive (49 +/- 5%) than in normotensive subjects (27 +/- 2%; P = 0.004). Sympathetically mediated venoconstriction elicited by deep breath was substantially potentiated by endothelin-1 in hypertensive (67 +/- 7% at 90 min) but not normotensive subjects (11 +/- 3% at 90 min; P = 0.001). Venoconstriction to endothelin-1 correlated positively with mean arterial pressure in the hypertensive subjects (r = 0.82; p = 0.001) but negatively in the normotensive subjects (r = -0.58; p = 0.047). Endothelin-1 may contribute to the reduction of venous compliance occurring in the early stages of essential hypertension and to the altered systemic hemodynamics in this condition.     

Short-term cortisol infusion in the brachial artery,with and without inhibiting 11 beta-hydroxysteroid dehydrogenase,does not alter forearm vascular resistance in normotensive and hypertensive subjects

BACKGROUND: Vascular tone is increased in primary hypertension, and glucocorticoids affect vascular tone. Local cortisol availability is modulated by activity of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD). As this activity may be decreased in patients with primary hypertension, vascular sensitivity to cortisol may be increased in these patients. We studied the acute effect of cortisol on forearm vascular resistance (FVR) by infusing cortisol directly into the brachial artery, both with and without inhibition of 11 beta-HSD, in normotensive and hypertensive subjects. DESIGN: Twenty normotensive volunteers and 20 patients with primary hypertension participated in the study. After a 10-min infusion of vehicle (glucose 5%), cortisol was infused into the brachial artery in three stepwise increasing doses (3.5, 10.5 and 35 microg per 100 mL of forearm volume), each for 10 min. Next, the participants received placebo or 500 mg glycyrrhetinic acid (GA) orally, and 150 min later the same infusion schedule was repeated. Forearm vascular resistance was measured during the last 5 min of the infused vehicle and of each dose. Arterial and forearm venous plasma samples for measurement of cortisol and cortisone were taken at the end of the infusions of glucose 5% and the highest cortisol dose. RESULTS: In both normotensive and hypertensive subjects, neither the infusion of cortisol nor the administration of GA changed FVR. Also 2 h after the cortisol infusion there remained no change in FVR in both the normotensive and hypertensive groups who received placebo. Following the infusion of the highest cortisol dose, total plasma cortisone levels in the venous plasma were decreased compared with levels in the arterial plasma (36 +/- 3 and 49 +/- 4 nmol L-1, respectively, P < 0.05). The protein-bound venous cortisone was 37.1 +/- 4.8 nmol L-1 during the vehicle compared with 23.9 +/- 3.7 nmol L-1 during the cortisol infusion (P < 0.01), whereas the free cortisone level was not altered by the cortisol infusion. CONCLUSIONS: In both normotensive and hypertensive subjects, high-dose cortisol infusion both with and without 11 beta-HSD inhibition did not change FVR either immediately or after 2 h. We could not demonstrate in vivo 11 beta-HSD activity in the forearm vascular tissues. When binding of cortisone to CBG is changed, e.g. during cortisol infusion, arterio-venous changes in cortisone cannot reliably be used to assess (alterations in) local 11 beta-HSD activity.     

Hysteresis of the venous pressure-volume relationship in the forearm of borderline hypertensive subjects.

1. The forearm venous pressure-volume relationship was studied in 14 young men with borderline hypertension and in 16 control subjects of the same age and sex. Strain-gauge plethysmography was used to evaluate volume changes after slow increases and decreases in distention, in order to estimate the amplitude of the hysteresis curve. 2. Compared with normotensive control subjects, subjects with borderline hypertension had significantly higher values of blood pressure, heart rate and forearm blood flow. 3. Baseline forearm venous tone was slightly, but not significantly, increased in borderline hypertensive subjects (21.35 +/- 6.53 versus 18.75 +/- 5.95 mmHg ml-1 100 ml-1) and was significantly enhanced after a cold pressor test. The increase was no higher in the borderline hypertensive subjects than in the normotensive control subjects. 4. The area of the hysteresis curve was significantly decreased (7.58 +/- 3.58 versus 10.34 +/- 5.67 arbitrary units; P = 0.0092) as was the extent of isotonic relaxation (creep) (0.28 +/- 0.11 versus 0.39 +/- 0.22 ml/100 ml; P = 0.0098) in borderline hypertensive subjects compared with control subjects. Both parameters were unaffected by the cold pressor test. 5. The study suggests that the viscous component of the venous wall is altered in young patients with borderline hypertension, indicating intrinsic changes in vascular segments which are not exposed to increased intraluminal pressure.