Endothelial dysfunction in small resistance arteries of patients with non-insulin-dependent diabetes mellitus.

OBJECTIVE: Arterial hypertension is frequently associated with the presence of endothelial dysfunction in human subcutaneous small resistance arteries, as evaluated by responses to acetylcholine or bradykinin; however it is not known whether patients with diabetes mellitus show similar alterations. Therefore, we have investigated endothelial function in subcutaneous arteries of normotensive subjects (NT), of patients with essential hypertension (EH), of patients with non-insulin-dependent diabetes mellitus (NIDDM), as well as of patients with both essential hypertension and non-insulin-dependent diabetes mellitus (NIDDM+EH). PATIENTS AND METHODS: All subjects were submitted to a biopsy of the subcutaneous fat Small arteries were dissected and mounted on a micromyograph. The media to lumen ratio (M/L) was calculated. A concentration-response curve to acetylcholine, to bradykinin as well as to the endothelium-independent vasodilator sodium nitroprusside were performed. We also evaluated the contractile response to endothelin-1. Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) plasma levels were also measured. RESULTS: The vasodilatation to acetylcholine and bradykinin (but not to sodium nitroprusside) was significantly and similarly reduced in EH, in NIDDM, and in NIDDM+EH compared with NT. The contractile response to endothelin-1 was similarly reduced in EH, in NIDDM and in NIDDM+EH. Plasma ICAM-1 and VCAM-1 concentrations were higher in EH, NIDDM and NIDDM+EH than in NT. CONCLUSIONS: An evident endothelial dysfunction was detected in patients with NIDDM, and the simultaneous presence of EH did not seem to exert an additive effect. The contractile responses to endothelin-1 were reduced possibly as a consequence of ET(A) receptor down-regulation.

Flow-mediated dilatation of the brachial artery and left ventricular geometry in hypertensive patients.

OBJECTIVES: In arterial hypertension, the spectrum of geometric patterns in the left ventricle may parallel the structural alterations detected in the carotid arteries and in subcutaneous small arteries. It has been also reported that hypertensive left ventricular hypertrophy (LVH) may be associated with endothelial dysfunction, as evaluated by the response of coronary or forearm vasculature to acetylcholine infusion. The aim of this study was to evaluate the flow-mediated vasodilatation (FMD) of the brachial artery, non-invasive estimate of endothelium-dependent vasodilatation according to left ventricular geometric adaptations in hypertensive patients. METHODS AND RESULTS: In 16 normotensive (nine males, seven females, aged 40-68 years) and in 78 hypertensive subjects (50 males, 28 females, aged 42-67 years), we performed an echocardiographic study for the measurement of left ventricular mass index (LVMI) and relative wall thickness (RWT); we measured to a high resolution the brachial artery diameter at rest, during reactive hyperaemia (5 min of brachial artery occlusion) and after sublingual glyceril trinitrate (GTN); brachial artery flow velocity was measured by pulsed Doppler. Twenty-six hypertensive patients had a normal LVMI (LVMI < 51 g/ m2.7) and geometry (RWT < 0.44), five had concentric remodelling (RWT > or = 0.44), and concentric and eccentric LVH were observed in 19 and 28 patients, respectively. FMD was reduced in hypertensive patients as compared with normotensive subjects (P< 0.01). No correlation was found between FMD and LVMI (r= -0.078) or RWT (r = 0.049); in addition, no difference in FMD was found among the left ventricular geometric patterns in hypertensive patients. CONCLUSIONS: In hypertensives, the presence of endothelial dysfunction is not associated with the LVH or with different left ventricular geometric patterns, suggesting that different and independent mechanisms may be responsible for the presence of LVH and of endothelial dysfunction.

The smoothness index, but not the trough-to-peak ratio predicts changes in carotid artery wall thickness during antihypertensive treatment.

BACKGROUND: It has recently been demonstrated that the smoothness index (SI) (the ratio between the average of the blood pressure changes computed for each hour of the recording and its standard deviation), a new and reproducible measure of the homogeneity of blood pressure reduction by antihypertensive treatment, has evident advantages over trough-to-peak ratio (T/P) in the prediction of the regression of left ventricular hypertrophy. Therefore we considered it to be worthwhile to compare the ability of SI and T/P to predict changes of the carotid artery intima-media thickness (IMT) during pharmacological treatment in patients with essential hypertension. METHODS: In 100 patients with essential hypertension, 24 h ambulatory blood pressure and carotid artery IMT were measured after 3 weeks of therapeutic wash-out and after 12 months of antihypertensive treatment (calcium antagonists, diuretics, angiotensin converting enzyme (ACE) inhibitors or beta-blockers). The homogeneity of the effect of treatment over blood pressure was evaluated by computing T/P and SI. RESULTS: Twenty-four hour blood pressure was significantly reduced by therapy, while, on average, a small but significant increase in indices of carotid artery wall thickness was observed. However, IMT was clearly reduced in patients with high SI. Statistically significant correlations were observed between changes in indices of carotid artery IMT during therapy and SI. No significant correlation was observed between indices of carotid artery morphology and T/P, basal 24 h blood pressure or changes in blood pressure during therapy. CONCLUSIONS: SI, but not T/P is the predictor of changes in carotid artery wall thickness. The information provided by SI is independent from basal blood pressure values. For carotid artery morphology, the smoothness of blood pressure reduction is even more important than its absolute change.

Structural alterations in subcutaneous small arteries of normotensive and hypertensive patients with non-insulin-dependent diabetes mellitus.

BACKGROUND: It is not presently known whether non-insulin-dependent diabetes mellitus (NIDDM) is associated with the presence of structural alterations in small arteries or whether the combination of hypertension and NIDDM may have an additive effect on endothelial dysfunction. Therefore, we investigated subcutaneous small arteries in 12 normotensive subjects (NT group), 18 patients with essential hypertension (EH group), 13 patients with NIDDM, and 11 patients with NIDDM and EH (NIDDM+EH group). METHODS AND RESULTS: Subcutaneous small arteries were evaluated by a micromyographic technique. The internal diameter, the media-to-lumen ratio, remodeling and growth indices, and the collagen-to-elastin ratio were calculated. Concentration-response curves to acetylcholine, bradykinin, the endothelium-independent vasodilator sodium nitroprusside, and endothelin-1 were performed. The media-to-lumen ratio was higher in the EH, NIDDM, and NIDDM+EH groups compared with the NT group. EH patients showed the presence of eutrophic remodeling, whereas NIDDM and NIDDM+EH patients showed 40% to 46% cell growth. The collagen-to-elastin ratio was significantly increased in the EH and NIDDM+EH groups compared with the NT group. The vasodilatation to acetylcholine and bradykinin was similarly reduced in EH, NIDDM, and NIDDM+EH groups compared with the NT group. The contractile responses to endothelin-1 were similarly reduced in EH, NIDDM, and NIDDM+EH patients. CONCLUSIONS: Our data suggest that the effects of NIDDM and EH on small artery morphology are quantitatively similar but qualitatively different and that the presence of hypertension in diabetic patients has little additive effect on small artery morphology and none on endothelial dysfunction.

Time course of apoptosis in small resistance arteries of spontaneously hypertensive rats.

OBJECTIVE: The time course of programmed cell death (apoptosis) in the vasculature of spontaneously hypertensive rats (SHRs) is still unclear. Moreover, no data are presently available about the possible inter-relationships between apoptosis and vascular remodelling. The aim of this study was to investigate the mesenteric small resistance arteries and large arteries (aortas) of SHRs and normotensive Wistar-Kyoto (WKY) rats at different ages, before and after the development of overt hypertension. METHODS: Twenty-four SHRs (4, 8 or 12 weeks old) and 24 age-matched WKY rats were included in the study. Blood pressure was measured non-invasively. Rats were killed by decapitation and segments of aortas and small mesenteric arteries were dissected free from the surrounding tissue. Mesenteric arteries were mounted on a micromyograph and structural characteristics were measured (media thickness, media:lumen ratio, etc.). Apoptotic cells in the tunica media of large and small vessels were then stained using modified TdT-mediated dUTP Nick-End Labeling (TUNEL). RESULTS: At 4 weeks of age no difference in the blood pressure and percentage of apoptosis in mesenteric arteries between SHRs and WKY rats was detected; however, the media:lumen ratio of mesenteric small resistance arteries was significantly greater in SHRs. At 8 and 12 weeks of age systolic blood pressure, media:lumen ratio and apoptosis rate in mesenteric small arteries was significantly higher in SHRs. The rate of apoptosis in the aortas was similar in the two strains at all three ages. CONCLUSIONS: An increased prevalence of apoptosis was observed in mesenteric small arteries of 8- and 12-week-old SHRs. It is possible that apoptosis may exert a role in small resistance artery remodelling during the development and establishment of hypertension.

High-dose, not low-dose insulin increases the vasoconstrictor effect of norepinephrine in spontaneously hypertensive rats: effects of antihypertensive treatment.

The effect of insulin on the vasoconstriction induced by norepinephrine is presently controversial. Therefore, the aims of our study were: (1) to evaluate the effect of low- and high-dose insulin on the concentration-response curve to norepinephrine in small resistance arteries of spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) before and after the development of hypertension, and (2) to evaluate the effects of antihypertensive treatment on vascular response to insulin and norepinephrine. Fifty-six rats were included in the study. Six SHR were treated with enalapril and 6 with candesartan cilexetil from the 4th to the 12th week of age, while 10 WKY and 14 SHR were kept untreated. Two additional groups of 10 untreated SHR and 10 WKY were killed at 4 weeks of age, in a prehypertensive phase. Mesenteric small arteries were dissected and mounted on a micromyograph. A dose-response curve to norepinephrine was performed at cumulative concentrations in the presence or absence of low- and high-dose insulin. We found that only high-dose insulin increased the vascular response to norepinephrine in 12-week-old SHR, but not in 4-week-old SHR or in age-matched WKY. The increased responsiveness to norepinephrine disappeared after preincubation of the vessels with a selective inhibitor of endothelin-1 type A receptors. After antihypertensive treatment with enalapril or candesartan cilexetil, the potentiation of the vasoconstrictor response to norepinephrine was abolished. In conclusion, insulin at high, nonphysiological doses seems to induce an increase in the reactivity to norepinephrine in mesenteric small arteries of SHR, possibly mediated by a local production of endothelin-1. Antihypertensive treatment with an ACE inhibitor or an angiotensin II receptor blocker may normalize this altered response. This mechanism may be relevant in the development of hypertension in SHR.

Effects of candesartan cilexetil and enalapril on structural alterations and endothelial function in small resistance arteries of spontaneously hypertensive rats.

It was previously observed that a significant regression of structural alterations and endothelial dysfunction in mesenteric small arteries of spontaneously hypertensive rats (SHRs) may be obtained after therapy with angiotensin-converting enzyme (ACE) inhibitors. It is not clear whether angiotensin II-type 1 receptor blockers may share this properties. We evaluated the effects of the ACE inhibitor enalapril and of the angiotensin II-receptor blocker candesartan cilexetil on structural alterations of mesenteric small resistance arteries, on cardiac mass, and on endothelial function in SHRs. Seventy-three rats were included in the study. Sixteen SHRs were treated with enalapril and 21 with candesartan cilexetil, whereas 18 Wistar-Kyoto (WKY) and 18 SHRs were untreated. Enalapril and candesartan cilexetil were administered in the drinking water from weeks 4 to 12 of age. Blood pressure was measured noninvasively every week. The rats were killed at the end of the treatment period, after 3 or 4 days of therapeutic washout. Heart weight/body weight ratio (HW/BW) was measured. Mesenteric arterioles were dissected and mounted on a micromyograph (Mulvany's technique). Then the media-to-lumen ratio (M/L) was evaluated. In addition, endothelium-dependent and endothelium-independent relaxation was evaluated by dose-response curves to acetylcholine (in the presence or absence of a bradykinin-receptor blocker and of indomethacin) and sodium nitroprusside. Systolic blood pressure was significantly reduced by both drugs, compared with untreated SHRs, although the hypotensive effect was greater with enalapril than with candesartan cilexetil. A significant reduction of M/L of mesenteric small arteries and of HW/BW was observed in SHRs treated with candesartan cilexetil or enalapril. A significant improvement of endothelial function, as evaluated by a dose-response to acetylcholine, was observed. The acetylcholine-induced vasodilatation was similar after addition to the organ bath of a selective blocker of bradykinin receptors, thus suggesting a minor role (if any) of the increased local availability of bradykinin, as a consequence of inhibition of ACE, in the improvement of endothelial function observed after enalapril treatment. In addition to a satisfactory antihypertensive effect observed with both drugs, candesartan cilexetil and enalapril were proven to be equally effective in reducing structural alterations in mesenteric small resistance arteries, in normalizing cardiac mass, and in improving endothelial function. The inhibition of bradykinin breakdown does not seem to be involved in the improvement of endothelial dysfunction observed with ACE inhibitors.

Effects of losartan and enalapril on small artery structure in hypertensive rats.

We evaluated the effects on cardiovascular structure of the angiotensin-converting enzyme (ACE) inhibitor enalapril and of the angiotensin II receptor blocker losartan, administered either at hypotensive or nonhypotensive dosage in spontaneously hypertensive rats (SHR). SHR were treated from ages 4 to 12 weeks with low-dose (1 mg x kg(-1) x d(-1)) enalapril, low-dose (0.5 mg x kg(-1) x d(-1)) losartan, high-dose (25 mg x kg(-1) x d(-1)) enalapril, or high-dose (15 mg x kg(-1) x d(-1)) losartan. Untreated WKY and SHR were also studied. Rats were killed at 13 weeks of age, and the heart was weighed. Mesenteric small arteries were dissected and mounted on a micromyograph for determination of media thickness and lumen diameter. In fixed arteries, cell volume, number of cells per segment length, and number of cell layers were measured using the unbiased "disector" method. Systolic blood pressure was significantly reduced by the high doses of both drugs, but the hypotensive effect was greater with enalapril than with losartan (P<0.05). In the high-dose enalapril and losartan groups, there were similar reductions in relative left ventricular mass, media/lumen ratio, and number of cell layers of resistance arteries; however, there were no differences in the cell volume or number of cells per segment length of resistance arteries. Low-dose enalapril did not affect systolic blood pressure or any of the structural parameters. The results show that the hypotensive effects of both losartan and enalapril were associated with outward remodeling of resistance arteries at the cellular level. The effect of losartan on resistance artery structure was equal to that of enalapril, despite the smaller hypotensive effect.

Effects of hypotensive and non-hypotensive doses of manidipine on structure, responses to endothelin-1 and ICAM-1 production in mesenteric small resistance arteries of spontaneously hypertensive rats.

OBJECTIVE: We have evaluated the effects of a new calcium channel blocker, manidipine, given at both high, hypotensive and low, non-hypotensive doses, on vascular morphology, response to endothelin-1 and ICAM-1 production in mesenteric small resistance arteries of spontaneously hypertensive rats (SHR). METHODS: Ten SHR were treated with manidipine 3 mg/kg per day (high dose) and 10 with manidipine 0.3 mg/kg/per day (low dose). The drug was administered by gavage from the 4th to 12th weeks of age. Eighteen Wistar-Kyoto (WKY) rats and 18 SHR were kept untreated as controls. Rats were killed at 13 weeks. Mesenteric small arteries were dissected and mounted on a micromyograph for determination of indexes of vascular structure (media thickness, wall thickness, media/lumen ratio). RESULTS: Systolic blood pressure was significantly reduced by the high dose of the drug, while no effect was observed with low-dose manidipine. A reduction in the media/lumen ratio was observed only in SHR treated with high-dose manidipine. The response to endothelin-1 in untreated SHR was significantly lower in comparison with WKY; a significant reduction was observed in SHR treated with high-dose manidipine. ICAM-1 vascular concentrations were higher in untreated SHR than in WKY controls. Both high- and low-dose manidipine reduced ICAM-1 concentrations toward normalization. CONCLUSIONS: Manidipine at high, hypotensive, but not at low, non-hypotensive doses has been proven to reduce structural alterations in mesenteric small resistance arteries, and to normalize vascular responses to endothelin-1. In addition, manidipine, at both low and high doses, may reduce ICAM-1 vascular production, thus suggesting a possible anti-atherogenic effect.