Independent Vasoconstriction Research Articles

Влияние нефрэктомии на реактивность артерий спонтанно гипертензивных крыс

The effect of nephrectomy on the SHR rat superior mesenteric artery (SMA) and internal carotid artery (ICA) segments constriction and dilatation ability was studied under isometric conditions using myograph. 5/6 nephrectomy (5/6 Nx) in the rats 3 months old was used as a model of the chronic kidney disease. Dilatation of the phenylephrine-precontracted segments was induced by acetylcholine (AСh) or sodium nitroprusside (SNP) in the absence and presence of potassium channels blockers (tetraethylammonium, glibenclamide) or methylene blue, a guanylyl-cyclase inhibitor. The phenylephrine-induced contraction was slightly reduced in the SMA from 5/6 Nx rats relative to the control ones and significantly decreased in the presence of methylene blue. This reaction in the ICA from 5/6 Nx rats was significantly less than in the control ones, both in the absence and in the presence of the blockers and the inhibitor. The effect of nephrectomy on the dilatatory reaction of both arteries caused by AСh or SNP was not found, but the constrictor reaction of ICA to AСh in the presence of glibenclamide significantly decreased in 5/6 Nx, but not in control rats. We conclude that the chronic kidney disease may weaken endothelium dependent and independent vasoconstriction in the ICA from SHR rats, as well as differently change the signaling pathways of this reaction in different types of arteries.

Влияние нефрэктомии на реактивность артерий крыс линии Wistar-Kyoto

The effect of nephrectomy on the Wistar Kyoto rat superior mesenteric artery (SMA) and internal carotid artery (ICA) segments constriction and dilatation ability was studied under isometric conditions using myograph. 5/6 nephrectomy (5/6 Nx) in the rats 3 months old was used as a model of the chronic kidney disease. Dilatation of the phenylephrine-precontracted segments was induced by acetylcholine (AСh) or sodium nitroprusside (SNP) in the absence and presence of potassium channels blockers (tetraethylammonium, glibenclamide) or methylene blue, a guanylyl-cyclase inhibitor. The phenylephrine-induced contraction was increased in the SMA but not in the ICA from 5/6 Nx rats. This reaction was not changed by the blockers and by inhibitor. The AСh-evoked reaction often had two phases. AСh-evoked dilatation phase of the reaction of the both arteries from 5/6 Nx rats have shown no difference from control (C) and was diminished by tetraethylammonium (in С and 5/6 Nx rats) and by methylene blue (in С rats). In 5/6 Nx rats, AСh-evoked constriction phase of the reaction in the absence of the blockers and inhibitor was significantly larger compared to С rats only in SMA, but in the absence of tetraethylammonium, it was significantly larger in both arteries. Glibenclamide diminished AСh-induced constriction of SMA from 5/6 Nx rats, while methylene blue diminished this constriction of ICA from control rats only. We conclude that the chronic kidney disease may increase endothelium dependent and independent vasoconstriction and may change signal pathways of this constriction, which may differ in the arteries of different types.

Dipeptidyl peptidase-4 inhibitor sitagliptin induces vasorelaxation via the activation of Kv channels and PKA

The present study investigated the vasorelaxant effects of sitagliptin, which is a dipeptidyl peptidase-4 (DPP-4) inhibitor in aortic rings pre-contracted with phenylephrine (Phe). Sitagliptin induced vasorelaxation in a concentration-dependent manner but the inhibition of voltage-dependent K+ (Kv) channels by pretreatment with 4-aminopyridine (4-AP) effectively reduced this effect. By contrast, the inhibition of inward rectifier K+ (Kir) channels by pretreatment with barium (Ba2+), large-conductance calcium (Ca2+)-activated K+ (BKCa) channels with paxilline, and adenosine triphosphate (ATP)-sensitive K+ (KATP) channels with glibenclamide did not change this effect. Although the application of SQ 22536, which is an adenylyl cyclase inhibitor, also did not change this effect, treatment with KT 5720, a protein kinase A (PKA) inhibitor, effectively reduced the vasorelaxant effects of sitagliptin. ODQ, which is a guanylyl cyclase inhibitor, and KT 5823, a protein kinase G (PKG) inhibitor, did not impact the effect. Furthermore, neither the inhibition of Ca2+ channels by pretreatment with nifedipine nor the inhibition of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) pumps by pretreatment with thapsigargin changed the effect. Similarly, the effects of sitagliptin were not altered by eliminating the endothelium, by pretreatment with a nitric oxide (NO) synthase inhibitor (L-NAME), or by inhibition of small- and intermediate-conductance Ca2+-activated K+ channels (SKCa and IKCa) using apamin and TRAM-34. Taken together, these results suggest that sitagliptin induces vasorelaxation by inhibiting both membrane potential (Em)-dependent and -independent vasoconstriction and activating PKA and Kv channels independently of PKG signaling pathways, other K+ channels, SERCA pumps, and the endothelium.

Combined aliskiren and L‐arginine treatment prevents vascular dysfunction in renovascular hypertension.

We investigate aliskiren, L‐arginine and both treatments on vascular reactivity in aortic rings. Hypertension was induced by clipping renal artery and animals were divided: Sham, 2‐kidney, 1‐clip (2K1C), 2K1C+aliskiren (ALSK), 2K1C+L‐arginine (L‐arg), and 2K1C+aliskiren and L‐arginine (ALSK+L‐arg) treatment for 4 weeks. Blood pressure was monitored and endothelium‐dependent and independent vasoconstriction and relaxation were assessed. ALSK+L‐arg decreased blood pressure, contractile response to phenylephrine and improved the acetylcholine relaxation. Endothelium removal and incubation with L‐NAME increased the response to phenylephrine in all groups, but magnitude was higher in ALSK+L‐arg group. Enalapril reduced phenylephrine response in 2K1C and ALSK groups and Losartan reduced in all of the groups. Apocynin reduced contractile response in 2K1C, ALSK and ALSK+L‐arg groups and incubation with superoxide dismutase reduced the response in 2K1C and ALSK groups. eNOS expression increase in 2K1C and L‐arg groups and iNOS increased only in 2K1C group compared with other groups. AT1 expression increase in 2K1C compared to Sham, ALSK and ALSK+L‐arg groups, AT2 expression increase in ALSK+L‐arg group compared to Sham and L‐arg groups, SOD2 increased in ALSK+L‐arg group compared to 2R1C, ALSK and L‐arg group, on the other hand, gp91phox decreased in ALSK+L‐arg compared with 2K1C and ALSK. In conclusion, combined ALSK+L‐arg was effective in preventing endothelial dysfunction of 2K1C hypertensive rats and the mechanisms responsible appear to be related to the modulation of local renin‐angiotensin system, which is associated with the reduction in endothelial oxidative stress.

Combined aliskiren and L-arginine treatment has antihypertensive effects and prevents vascular endothelial dysfunction in a model of renovascular hypertension.

Angiotensin II is a key player in the pathogenesis of renovascular hypertension, a condition associated with endothelial dysfunction. We investigated aliskiren (ALSK) and L-arginine treatment both alone and in combination on blood pressure (BP), and vascular reactivity in aortic rings. Hypertension was induced in 40 male Wistar rats by clipping the left renal artery. Animals were divided into Sham, 2-kidney, 1-clip (2K1C) hypertension, 2K1C+ALSK (ALSK), 2K1C+L-arginine (L-arg), and 2K1C+ALSK+L-arginine (ALSK+L-arg) treatment groups. For 4 weeks, BP was monitored and endothelium-dependent and independent vasoconstriction and relaxation were assessed in aortic rings. ALSK+L-arg reduced BP and the contractile response to phenylephrine and improved acetylcholine relaxation. Endothelium removal and incubation with N-nitro-L-arginine methyl ester (L-NAME) increased the response to phenylephrine in all groups, but the effect was greater in the ALSK+L-arg group. Losartan reduced the contractile response in all groups, apocynin reduced the contractile response in the 2K1C, ALSK and ALSK+L-arg groups, and incubation with superoxide dismutase reduced the phenylephrine response in the 2K1C and ALSK groups. eNOS expression increased in the 2K1C and L-arg groups, and iNOS was increased significantly only in the 2K1C group compared with other groups. AT1 expression increased in the 2K1C compared with the Sham, ALSK and ALSK+L-arg groups, AT2 expression increased in the ALSK+L-arg group compared with the Sham and L-arg groups, and gp91phox decreased in the ALSK+L-arg group compared with the 2K1C and ALSK groups. In conclusion, combined ALSK+L-arg was effective in reducing BP and preventing endothelial dysfunction in aortic rings of 2K1C hypertensive rats. The responsible mechanisms appear to be related to the modulation of the local renin-angiotensin system, which is associated with a reduction in endothelial oxidative stress.

Hemodynamic Mechanism of Ventricular Hypertrophy in Hypertension

Arterial hemodynamic assessments with technique of spectral analysis can obtain complete hemodynamic parameters including steady and pulsatile components. The steady parameters include arterial pressure (AP), heart rate, cardiac output, stroke volume and total peripheral resistance (TPR). Parameters of pulsatile hemodynamics are characteristic impedance (Zc), arterial compliance (Cm) and pulse wave reflection (Pb) etc. Studies of ventricular hypertrophy (VH) and arterial hemodynamics have disclosed several important findings. Hypertension in spontaneously hypertensive rat (SHR) and human subjects causes functional abnormalities in the resistance and Windkessel vessels. The extent of VH in SHR and hypertensive subjects was not correlated with AP and TPR, but positively correlated with pulsatile hemodynamic factors such as Zc and Pb. Many antihypertensive and vasodilators were capable of reducing the AP, but did not improve the VH. We have also investigated the effects of vasodilatory agents such as nifedipine (a calcium channel blocker), propranol (a non-selective β-adrenergic blocker) and atenol (a selective β-adrenergic inhibitor) on the arterial hemodynamics and VH. In addition, the effects of acute and chronic nitric oxide (NO) deprivation with Nω-nitro-L-arginine methyl ester (L-NAME) on the arterial hemodynamics and VH were evaluated. We compared the endothelium-dependent and -independent vasodilation to acetylcholine, sodium nitroprusside and S-nitroso-N-acetylpenicillanine and the endothelium-dependent or -independent vasoconstriction to norepinephrine and phenylephrine between SHR and normotensive Wistar Kyoto strain. In SHR with long-term administration of L-NAME, VH was associated with decreases in left ventricular cGMP and nitrate/nitrite accompanying increase in collagen content. Coadministration of NO precursor L-arginine improved the VH and fibrosis. In VH caused by long-term L-NAME, the LW/BW ratio, total number, numerical density and size of cardiomyocytes were correlated well with both steady and pulsatile hemodymanics. Aortic stiffness has significant impact on the cardiovascular risks. We simulated aortic stiffness by applying silicon gel embedding of the abdominal and/or thoracic aorta. Aortic stiffness did not affect the blood pressure and the steady hemodynamics. It caused VH associated with increases in the pulsatile hemodynamics. The extent of VH (LVW/BW, total number, numerical density, size of cardiomyocytes and collagen volume fraction) was correlated with the pulsatile hemodynamics (impedance, pulse wave velocity and wave reflection). The finding further supports the contention that blood pressure is not the determinant of VH. The ventricular afterload is the major cause of VH. The hemodynamic consequences of ovariectomy (Ovx), menopause and estrogen replacement were investigated. Ovx increased body weight, LVW/BW ratio, Zc and Pb, but decreased Cm. These changes were reversed by estrogen replacement. For steady hemodynamics, Ovx did not much alter the systolic, mean and diastolic pressure. The pulse pressure was slightly elevated. There was large increase in TPR. Again, these changes were reversed by estrogen supplement. The implication of these findings was that menopause tends to exert vasoconstrictory effects on the resistance and Windkessel vessels. On the contrary, estrogen possesses a vasodilatory influence on the systemic vessels.

The differential extraction and immunoluminometric assay of Urotensin II and Urotensin-related peptide in heart failure

Urotensin II (UTN) is a cyclic eleven amino acid peptide that can induce endothelial independent vasoconstriction and endothelial dependent vasodilatation in human vasculature. The cyclic part of the peptide is composed of six amino acids. Similarly, Urotensin Related Peptide (URP) is only eight amino acids long but shares the identical ring structure to UTN. Plasma UTN has been shown to be raised in patients with chronic heart failure (CHF) suggesting a potential role of the peptide system in the pathophysiology of heart failure. Given their similar structures, techniques measuring plasma UTN may also be simultaneously detecting URP and could provide a misrepresentation of true UTN and URP levels in patients’ plasma. Thus we describe the development of a solid phase extraction technique that can differentially extract UTN and URP from human plasma so that they can be assayed separately using non-radioactive immunoluminometric assays. This reliable and sensitive protocol was utilized to characterise the plasma of 20 healthy controls and 20 patients admitted with acute heart failure (AHF). The groups were age and sex matched. Plasma UTN was significantly raised in patients with AHF on admission when compared to controls (median 1.29 [range 0.50–5.55]pmol/L vs 0.50 [0.50–3.33]pmol/L, p=0.019). Likewise plasma URP was significantly higher in the heart failure group on admission (8.38 [1.30–66.80]pmol/L vs 2.25 [1.30–14.40]pmol/L, p<0.005). This suggests a role for both members of the Urotensin peptide system in acute heart failure.

Pathogenesis of cerebral vasospasm following aneurysmal subarachnoid hemorrhage: Putative mechanisms and novel approaches

Cerebral vasospasm is a potentially incapacitating or lethal complication in patients with aneurysmal subarachnoid hemorrhage (SAH). The development of effective preventative and therapeutic interventions has been largely hindered by the fact that the underlying pathogenic mechanisms of cerebral vasospasm remain poorly understood. However, intensive research during the last 3 decades has identified certain mechanisms that possibly play a role in its development. Experimental data suggest that calcium-dependent and -independent vasoconstriction is taking place during vasospasm. It appears that the breakdown products of blood in the subarachnoid space are involved, through direct and/or indirect pathways, in the development of vasospasm after SAH. Free radicals reactions, an imbalance between vasoconstrictor and vasodilator substances (endothelium derived substances, e.g., nitric oxide, endothelin; arachidonic acid metabolites, e.g., prostaglandins, prostacyclin), inflammatory processes, an upheaval of neuronal mechanisms that regulate vascular tone, endothelial proliferation, and apoptosis have all been put forward as causative and/or pathogenic factors. Translational research in the field of vasospasm has traditionally aimed to identify agents/interventions in order to block the cascades initiated after SAH. The combination of novel approaches such as cerebral microdialysis, magnetic resonance spectroscopy, proteomics, and lipidomics could serve a dual purpose: elucidating the complex pathobiochemistry of vasospasm and providing clinicians with tools for early detection of this feared complication. The purpose of this Mini-Review is to provide an overview of the pathogenesis of cerebral vasospasm and of novel approaches used in basic and translational research.

Attenuation of receptor-dependent and -independent vasoconstriction in the human radial artery☆

Vasodilator strategies used to treat bypass grafts in the operating theatre, such as nitrates, phosphodiesterase inhibitors and calcium channel antagonists have a broad but short-lived effect against a variety of vasoconstrictor stimuli. Treatments that react irreversibly with proteins modulating vasoconstriction have the advantage that their effects can last well into the postoperative period. In addition systemic effects are avoided as the treatment is localised to the treated graft. This study investigated the use of two clinically applied drugs; fluphenazine (SKF7171A, HCl), an irreversible calmodulin antagonist and minoxidil sulphate, an irreversible potassium channel opener. Treatments were tested against receptor and non-receptor-mediated contraction in the human radial artery. Isometric tension was measured in response to angiotensin II, KCl and vasopressin in 108 radial artery rings (taken from 31 patients undergoing coronary artery bypass grafting). Control responses were compared with rings pretreated with fluphenazine or minoxidil sulphate. Vasopressin responses were also compared in the presence of glyceryl trinitrate or the reversible Rho kinase inhibitor Y27632. Fluphenazine pretreatment significantly suppressed vasoconstriction to all agonists tested. Maximal responses to angiotensin II, vasopressin and KCl were reduced by 42+/-19%, 35+/-8% and 48+/-15% respectively, without any measurable effect on the EC(50). Minoxidil sulphate showed no discernable effect. Vasopressin-induced contraction was also reduced by high levels of glyceryl trinitrate (220 microM; 50 microg/ml) or 10 microM Y27632. The irreversible calmodulin antagonist fluphenazine has potential to be developed as an inhibitor of contraction in arterial graft vessels. The involvement of Rho kinase indicates that other vasoconstrictors and surgical stress can sensitize radial artery to vasopressin-induced contraction. Strategies targeting this pathway also have future potential.

Cardiotoxicity of 5-Fluorouracil

Cardiac side effects of the cytostatic agent 5-fluorouracil (5-FU) have an incidence of 1.2-7.6%. Potentially, arrhythmias, myocardial infarction and sudden cardiac death could occur. Life-threatening cardiotoxicity is rarely observed with a frequency <1%. Cardiotoxicity of 5-FU seems to differ from well known effects of other cytostatics, e.g., anthracyclines. Myocardial ischemia was suggested as potential mechanism due to occasionally observed ECG alterations during 5-FU administration. Experimental studies revealed potential mechanisms of cardiotoxicity ranging from direct toxic effects on vascular endothelium involving endothelial NO synthase leading to coronary spasms and endothelium independent vasoconstriction via protein kinase C. In addition, rheological side effects have to be considered. Coronary artery disease is judged to increase the risk of cardiac side effects. Despite lack of prospective trials, verapamil type calcium antagonists as well as nitrates seem to be useful for treatment of 5-FU induced coronary spasms. In addition, modification of the cytostatic regimen has to be considered in patients who had been symptomatic. It could be assumed that 5-FU toxicity is reversible in the majority of cases when acute complications, e.g., arrhythmias, are resolved.

Different Prostanoids Are Involved in Bradykinin-Induced Endothelium-Dependent and -Independent Vasoconstriction in Rat Mesenteric Resistance Arteries

Mechanisms underlying bradykinin-induced vasoconstriction were investigated in rat perfused mesenteric vascular beds with active tone. In preparations with intact endothelium, bolus injections of bradykinin (1 to 1,000 pmol) dose-dependently produced three-phase vascular effects, which consisted of a first-phase vasodilation followed by a second-phase vasoconstriction and a subsequent third-phase vasodilation; these effects were abolished by FR172357 (bradykinin B2-receptor antagonist), but not by des-Arg9-[Leu8]-bradykinin (bradykinin B1-receptor antagonist). In preparations with intact endothelium, indomethacin (cyclooxygenase inhibitor), seratrodast (thromboxane A2 (TXA2)-receptor antagonist), ONO-3708 (TXA2/prostaglandin H2 (PGH2)-receptor antagonist) or ozagrel (TXA2 synthesis inhibitor) markedly inhibited the bradykinin-induced vasoconstriction. In preparations without endothelium, the bradykinin-induced vasoconstriction was abolished by indomethacin and ONO-3708, while seratrodast and ozagrel had no effect. These results suggest that the endothelium-dependent vasoconstriction of bradykinin is mainly mediated by TXA2 and that prostanoids other than TXA2, probably PGH2, in mesenteric vascular smooth muscle are responsible for bradykinin-induced endothelium-independent vasoconstriction.

Coronary responses to endothelin-1 and acetylcholine during partial coronary ischaemia and reperfusion in anaesthetized goats

To examine coronary reactivity to acetylcholine and endothelin-1 (ET-1) during partial ischaemia and reperfusion, flow in the left circumflex coronary artery was measured electromagnetically, and coronary partial ischaemia was induced by stenosis of this artery in anaesthetized goats. In eight animals not treated with N(G)-nitro-l-arginine methyl ester (l-NAME), coronary stenosis reduced coronary flow by 45%, mean arterial pressure by 16% and coronary vascular conductance by 34%. During this ischaemia, coronary vasodilatation to acetylcholine (0.003-0.1 microg) and sodium nitroprusside (SNP; 1-10 microg) was markedly reduced, and coronary vasoconstriction to ET-1 (0.01-0.3 nmol) was attenuated. After 30 min of reperfusion, coronary flow, mean arterial pressure and coronary vascular conductance remained decreased, and the effects of acetylcholine, SNP and ET-1 were as in control animals. In six goats treated with N(G)-nitro-l-arginine methyl ester, coronary stenosis reduced coronary flow by 26% and coronary vascular conductance by 24%, but did not affect mean arterial pressure. During this ischaemia, coronary vasodilatation to acetylcholine and SNP was also markedly reduced, but vasoconstriction to ET-1 was unaffected. After 30 min of reperfusion, coronary flow and coronary vascular conductance remained decreased and mean arterial pressure was normal; in addition, the effects of acetylcholine were lower, those of SNP were similar and those of ET-1 were higher than in control animals. Therefore partial ischaemia reduces the coronary vasodilator reserve and blunts coronary vasoconstriction to ET-1, and reperfusion does not alter the endothelium-dependent and -independent coronary vasodilatation or vasoconstriction to ET-1.

Calcium Influx-Dependent and -Independent α1-Adrenoceptor-Mediated Processes of Vasoconstriction In Vivo Do Not Operate via Different α1-Adrenoceptor Subtypes

Summary: In pithed rats, the selective α1-adrenoceptor agonists St 587 and cirazoline show preponderant calcium influx-dependent and -independent vasoconstriction, respectively. By using these agonists, selective (competitive) antagonists for either process of vasoconstriction were sought. For this purpose, antagonism was analyzed for eight structurally different antagonists (prazosin, BE 2254, AR-C239, R 28935, corynanthine, phentolamine, sulpiride, and chlorpromazine) opposing the pressor responses evoked by cirazoline and St 587. Where pA2 values ( -log dose antagonist evoking a twofold shift for the agonist dose-response curve) could be calculated, no significantly different pA2 values against either agonist resulted. However, with respect to the slopes of the Schild plots, deviations from unity were found for prazosin, R 28935, AR-C239, sulpiride, and chlorpromazine, but not uniformly against both agonists. Following treatment with phenoxybenzamine (PB) (30 μg/kg) and nifedipine (1 mg/kg), which produced calcium influx-sensitive and -insensitive vasoconstriction to cirazoline, respectively, Schild plots were constructed for BE 2254, prazosin, and chlorpromazine. Using cirazoline as an agonist, unity slopes were now obtained for prazosin and chlorpromazine. The Schild plots of BE 2254 versus cirazoline after PB or nifedipine administration, however, exhibited a slope deviating from unity. For prazosin and chlorpromazine, identical pA2 values still resulted against both processes of vasoconstriction to cirazoline. The results are compatible with the view that α1-adrenoceptors mediating calcium influx-dependent and -independent vasoconstriction in vivo are not distinctly different entities, but are separate recognition sites of the same receptor.

Calcium Influx-Dependent and -Independent α1-Adrenoceptor-Mediated Processes of Vasoconstriction In Vivo Do Not Operate via Different α1-Adrenoceptor Subtypes

Summary: In pithed rats, the selective α1-adrenoceptor agonists St 587 and cirazoline show preponderant calcium influx-dependent and -independent vasoconstriction, respectively. By using these agonists, selective (competitive) antagonists for either process of vasoconstriction were sought. For this purpose, antagonism was analyzed for eight structurally different antagonists (prazosin, BE 2254, AR-C239, R 28935, corynanthine, phentolamine, sulpiride, and chlorpromazine) opposing the pressor responses evoked by cirazoline and St 587. Where pA2 values ( -log dose antagonist evoking a twofold shift for the agonist dose-response curve) could be calculated, no significantly different pA2 values against either agonist resulted. However, with respect to the slopes of the Schild plots, deviations from unity were found for prazosin, R 28935, AR-C239, sulpiride, and chlorpromazine, but not uniformly against both agonists. Following treatment with phenoxybenzamine (PB) (30 μg/kg) and nifedipine (1 mg/kg), which produced calcium influx-sensitive and -insensitive vasoconstriction to cirazoline, respectively, Schild plots were constructed for BE 2254, prazosin, and chlorpromazine. Using cirazoline as an agonist, unity slopes were now obtained for prazosin and chlorpromazine. The Schild plots of BE 2254 versus cirazoline after PB or nifedipine administration, however, exhibited a slope deviating from unity. For prazosin and chlorpromazine, identical pA2 values still resulted against both processes of vasoconstriction to cirazoline. The results are compatible with the view that α1-adrenoceptors mediating calcium influx-dependent and -independent vasoconstriction in vivo are not distinctly different entities, but are separate recognition sites of the same receptor.