Endothelium-dependent vasodilatation in treated and untreated hypertensive subjects

Systolic and diastolic hypertension impair endothelial vasodilatory function in different types of vessels in the elderly: the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study

BACKGROUND

Endothelium-dependent vasodilation (EDV) is known to be impaired in middle-aged hypertensive individuals, but less is known regarding hypertension in the elderly.

OBJECTIVE

In the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study, different techniques to evaluate EDV in resistance and conduit arteries were applied in elderly subjects and were related to the type of hypertension.

DESIGN AND METHODS

In this population-based study, 1016 subjects aged 70 years were evaluated by the invasive forearm technique with acetylcholine (EDV), brachial artery ultrasound to assess flow-mediated dilatation (FMD) and pulse wave analysis with a beta-2 receptor agonist challenge, terbutaline. Those without antihypertensive treatment were divided into three groups: normotensive individuals (n = 256), and those with isolated systolic hypertension (n = 309) or combined systolic/diastolic hypertension (n = 79).

RESULTS

Compared with normotensive individuals, EDV was reduced in those with combined systolic/diastolic hypertension only (P = 0.0019), whereas FMD was mainly reduced in those with isolated systolic hypertension (P = 0.013). Furthermore, in regression analysis, EDV was related to diastolic blood pressure only (r = -0.10, P = 0.017), whereas FMD was mainly related to systolic blood pressure (r = -0.13, P = 0.0023). The pulse wave-based method to analyse vasoreactivity was not consistently affected by hypertension.

CONCLUSIONS

In elderly subjects, systolic hypertension mainly impairs conduit artery endothelial vasodilatory function, whereas diastolic hypertension mainly induces dysfunction in resistance arteries.

Endothelium-dependent vasodilatation in forearm is impaired in stroke patients

OBJECTIVES

To investigate endothelium-dependent vasodilatation (EDV) in stroke patients.

DESIGN

Cross-sectional.

SETTING

University referral hospital.

SUBJECTS

We studied 23 stroke patients (65-75 years old) who did not have atrial fibrillation or Warfarin treatment. Forty-six age- and sex-matched healthy controls and another 32 controls matched also for hypertension and medication were used for comparisons. METHODS. Endothelium-dependent vasodilatation was measured with venous occlusive plethysmography of forearm blood flow during intra-brachial infusion of acetylcholine. Endothelium-independent vasodilatation (EIDV) was evaluated by infusion of sodium nitroprusside.

RESULTS

Stroke patients showed significantly lower EDV (P < 0.001) compared with healthy controls when measured with acetylcholine-stimulated forearm blood flow. The difference between these groups remained significant also after correction for blood pressure, body mass index, blood glucose and cholesterol. There was also significant difference in EDV between hypertension-matched controls and healthy controls. However, EIDV was significantly reduced in stroke patients (P < 0.01), but not in the hypertensive group, when compared with healthy controls.

CONCLUSION

An impaired EDV was seen in both stroke patients and hypertensive-matched controls, while an impaired EIDV was seen in the stroke patients only, suggesting a more severe vasodilatory dysfunction in stroke patients than could be explained by a high blood pressure only.

EFFECT OF NOS INHIBITION ON RETINAL ARTERIAL AND CAPILLARY CIRCULATION IN EARLY ARTERIAL HYPERTENSION

BACKGROUND

Arterial hypertension is involved in the pathogenesis of end organ damage by influencing the ability of the vascular endothelium to produce nitric oxide (NO). This study analyzes changes of retinal and systemic NO-dependent circulation parameters by inhibiting nitric oxide synthase (NOS) in both hypertensive and normotensive individuals.

METHODS

In a double-blind crossover trial, 19 hypertensive patients (H, age 28.2 +/- 0.9 years) and 19 normotensive controls (N, age 26.9 +/- 0.9 years) were randomized treated either with candesartan or placebo. Both retinal capillary flow (RCF) and mean blood flow velocity of the central retinal artery (VCRA) were registered before and after NOS inhibition with N-monomethyl-L-arginine (L-NMMA, 3 mg/kg). In a subpopulation mean arterial pressure (MAP), cardiac output (CO), and the total peripheral resistance (TPR) were determined simultaneously.

RESULTS

Changes from baseline: In normotensive and hypertensive subjects infusion of L-NMMA led to an increase of MAP (N, +13.3 +/- 1.8%, P < 0.01; H, +14.3 +/- 2.4%, P < 0.01) and TPR (N, +36.9 +/- 3.8%, P < 0.01; H, +45.0 +/- 4.5%, P < 0.01), and to a decrease of CO (N, -21.1 +/- 1.5%, P < 0.01; H, -24.6 +/- 2.3%, P < 0.01). The L-NMMA effect on VCRA and RCF differed between controls and hypertensives. VCRA changed by + 17.3 +/- 6.2% (P < 0.05) and RCF by -7.3 +/- 3.0% (P < 0.05) in controls. In hypertensive subjects corresponding results were + 9.5 +/- 5.2% (P = NS) and + 2.7 +/- 3.8% (P = NS), respectively. The decrease of RCF due to L-NMMA was reduced in hypertension as compared to controls (P < 0.05). The calculated cross-sectional area of CRA was reduced by -58.7% in controls and increased by + 31.1% in hypertensive subjects. There was no significant correlation between the flow in the systemic and retinal circulation.

CONCLUSION

Only normotensives L-NMMA induces an acceleration of VCRA due to a probable vasoconstriction of the central retinal artery and despite of a reduced RCF. Already in early hypertension the NOS-dependent vascular tone in retinal arteries and capillaries is impaired. The regulation of the retinal capillary flow appeared to be independent from systemic circulation.

Early endothelial dysfunction following renal mass reduction in rats

BACKGROUND

Endothelial dysfunction has been previously described in severely hypertensive rats with renal mass reduction (RMR) receiving large dietary Na loads. Because hypertension and Na loading reduce endothelium-dependent vasodilation, the effect of renal failure per se is unclear.

METHODS

Responses to acetylcholine in noradrenaline-contracted isolated perfused mesenteric arteries were studied. Vessels were obtained from RMR rats kept on a normal diet, 3 and 10 days after surgery, and the results were compared with those from sham-operated rats (SN). The role of three putative mediators of endothelium-dependent vasodilation was assessed using: L-NAME (10(-4) mol L(-1)); indomethacin (INDO, 10(-5) mol L(-1)); and a mixture of charybdotoxin and apamin (C/A, both 10(-7) mol L(-1)), inhibitors of Ca-activated K-channels to mediate the effects of endothelium-derived hyperpolarizing factor (EDHF).

RESULTS

Response to acetylcholine but not that to nitroprusside (endothelium-independent) was decreased in RMR. L-NAME reduced further acetylcholine relaxations in SN but not in RMR. By contrary, INDO decreased acetylcholine vasodilation in RMR but had no effect in SN. C/A had similar effects in the SN and RMR rats. The levels of 6-keto prostaglandin F1alpha were elevated in the urine of the RMR rats and were perfusate from the RMR vessels.

CONCLUSION

Endothelial dysfunction occurs early after RMR, even when systolic blood pressure is only minimally elevated and Na intake is normal. This alteration may be because of decreased availability of nitric oxide, partially compensated by increased prostacyclin production.

Improvement of endothelial function by amlodipine and vitamin C in essential hypertension

BACKGROUND

The effects of antihypertensive agents on endothelial function have not been fully evaluated in human hypertension and data on the forearm circulation of humans are controversial. The aim of this study was (1) to evaluate the endothelial function in hypertensive patients (2) to investigate whether vitamin C administration has any benefit on the endothelial function and (3) to determine whether treatment with calcium antagonist improves endothelial dysfunction in hypertensive patients.

METHODS

The endothelial function was estimated using venous occlusion plethysmography (VOP) in 8 hypertensive patients and 8 healthy volunteers. The patients in the hypertension group were treated with amlodipine, then examined again. The change of forearm blood flow (FBF) was measured with acetylcholine infusion through brachial artery and also with intra-arterial vitamin C.

RESULTS

Forearm blood flow response to acetylcholine was significantly enhanced with intra-arterial infusion of vitamin C in hypertensive group before antihypertensive treatment. Co-infusion of L-NMMA, an inhibitor of nitric oxide synthase, blunted forearm blood flow response to acetylcholine. After treatment with amlodipine for 2 months in hypertensive group, endothelium-dependent vasorelaxation to acetylcholine was significantly improved compared to pretreatment, and vitamin C did not affect the improved endothelial function by amlodipine treatment.

CONCLUSION

Vitamin C (acutely) and amlodipine (chronically) improved endothelial function in hypertensive patients. These results suggest that increased oxidative stress, at least in part, may be involved in the decreased endothelial function in hypertension.

Effects of angiotensin converting enzyme inhibitor and calcium antagonist on endothelial function in patients with essential hypertension

The endothelium plays an important role in maintaining vascular tone and function. Essential hypertension is associated with alterations in endothelial function. The effects of antihypertensive agents on endothelial function have not been fully evaluated in human hypertension and data on the forearm circulation of humans are controversial. The aim of this study was to determine whether treatment with an angiotensin converting enzyme (ACE) inhibitor or a calcium antagonist improves endothelial dysfunction in hypertensive patients and whether the mechanism involved could be related to antioxidant activity. Endothelial function was estimated using venous occlusion plethysmography in 18 hypertensive patients and 11 healthy volunteers. The patients in the hypertension group were treated with enalapril or amlodipine. The change of forearm blood flow (FBF) was measured during acetylcholine infusion through the brachial artery and also during intra-arterial vitamin C infusion to explore the effects of vitamin C on responses to acetylcholine. FBF response to acetylcholine was significantly enhanced by intra-arterial infusion of vitamin C in the hypertensive group before antihypertensive treatment. Co-infusion of L-NMMA(N(G)-monomethyl-L-arginine), an inhibitor of nitric oxide synthase, blunted forearm blood flow response to acetylcholine. After antihypertensive treatment with enalapril or amlodipine for 2 months in the hypertensive group, endothelium-dependent vasorelaxation (vasodilatory response to acetylcholine) was significantly improved. Even though the mechanisms leading to depressed endothelial function in essential hypertension remain to be elucidated, our study shows that treatment with an ACE inhibitor or a calcium antagonist resulted in demonstrable improvement by a mechanism that is probably related to antioxidant activity.

Nitric oxide dependence of renal blood flow in patients with renal artery stenosis

In ischemia, nitric oxide (NO) production is increased, possibly to preserve flow. The role of NO was investigated in hypertensive patients with or without renal artery stenosis (RAS). Fifty-five hypertensive patients scheduled to undergo diagnostic renal angiography underwent mean renal blood flow (MRBF) measurements before and after an intrarenal injection of the NO synthase blocker N(g)-monomethyl-L-arginine (L-NMMA) at 0.03 microg/kg, before angiography. A dose-response study indicated that this dose of L-NMMA significantly blocked NO synthesis. MRBF was measured at baseline and 1, 5, 10, and 20 min after L-NMMA treatment. On the basis of the angiographic results, patients were divided into three diagnostic categories, i.e., essential hypertension (n = 26), unilateral RAS (n = 16), or bilateral RAS (n = 8). In essential hypertension, MRBF was decreased by 18 +/- 4% at 20 min. In unilateral RAS, L-NMMA did not affect MRBF in the stenotic kidney but reduced MRBF in the nonstenotic kidney by 40 +/- 9% at 20 min. In bilateral RAS, L-NMMA reduced flow by 32 +/- 14% at 20 min. In the nonstenotic kidney in unilateral RAS, a positive correlation was observed between the effect of NO blockade on MRBF and arterial renin levels (P = 0.009). In the stenotic kidney, in contrast, this correlation was inverse (P = 0.007). In conclusion, MRBF depends on NO in hypertensive patients, except in the stenotic kidney in unilateral RAS. In the nonstenotic kidney in unilateral RAS, NO bioavailability is increased. It is suggested that a compensatory mechanism, regulated by NO and possibly angiotensin II, may preserve renal function.

Endothelium-dependent vasoactive modulation in the ophthalmic circulation

The vascular endothelium is strategically located between the circulating blood and the vascular smooth muscle cells. Different agonists or stimuli transported by the circulating blood can trigger the endothelium to release potent relaxing (nitric oxide, prostacyclin, endothelium-derived hyperpolarizing factor) or contracting factors (endothelin, cycloxygenase products). These endothelium-derived vasoactive factors can modulate blood flow locally. Heterogeneity exists from one vascular bed to the other, or even between vessels, in the agonists able to stimulate the release of endothelium-derived vasoactive factors. In the ophthalmic circulation, nitric oxide and endothelin are strong vasoactive modulators. In many vascular diseases that are of importance in ophthalmology (hypercholesterolemia, arteriosclerosis, hypertension, diabetes, vasospastic syndrome, ischemia and reperfusion, etc) the function of the endothelium can be impaired. There exist different drugs that can modulate the vasoactive function of the vascular endothelium. In other words, it appears that the vascular endothelium plays an important role in both the physiology and pathophysiology of the regulation of blood flow. The modulation of this regulatory system by different drugs might open new therapeutical approaches to treat vascular disorders in ophthalmology.