Effects of CGS-15943A on the relaxations produced by adenosine analogs in human blood vessels

The antagonistic effects of CGS-15943A on the relaxations produced by adenosine and its analogs in human blood vessels were investigated in vitro. Donor hearts were the source of coronary arteries, whereas the internal mammary arteries and saphenous veins were obtained from patients undergoing coronary bypass surgery. Adenosine and its analogs, 5'-N-ethylcarboxamidoadenosine (NECA) and 2-chloroadenosine (CAD), produced concentration-dependent relaxations in KCl-contracted coronary rings. CGS-15943A antagonized, significantly, the relaxations produced by adenosine, NECA and CAD in coronary arteries. Similarly, the adenosine receptor antagonist, 8-phenyltheophylline (8PT, 10-mumol/l), caused a significant attenuation of the relaxing responses to adenosine, NECA and CAD in coronary arteries. In rings obtained from internal mammary arteries and saphenous veins, adenosine, NECA and CAD all produced concentration-dependent relaxations. These relaxations were smaller in magnitude than those obtained in coronary arteries, and were slightly greater in rings contracted with 10 mumol/l prostaglandin F2 alpha (PGF2 alpha) as compared to 35 mmol/l KCl. However, the mammary arteries and saphenous veins relaxed completely in response to 100 mumol/l papaverine. CGS-15943A (10 mumol/l) did not antagonize the relaxing effects of adenosine and its analogs in these vessels. The results show that coronary arteries are more responsive than mammary arteries or saphenous veins to the relaxing effects of adenosine analogs and that these relaxing responses are dependent on the contracting agent. Furthermore, CGS-15943A demonstrated antagonism of the adenosine response in coronary arteries.     

Vasorelaxant effect of mexiletine in mesenteric resistance arteries of rats.

1. The vascular action of mexiletine, a class Ib antiarrhythmic agent, was investigated in the mesenteric resistance arteries of rats. 2. The second order branch of the mesenteric artery was cut into rings and changes in isometric tension were recorded. 3. Mexiletine (10(-6) -10(-3) M) evoked concentration-dependent, endothelium-independent relaxations in arteries contracted with noradrenaline. 4. Mexiletine (10(-4) M) did not affect the contraction induced by noradrenaline in Ca(2+)-free solution, while the compound inhibited the contraction induced by CaCl2 in noradrenaline-activated arteries. 5. The relaxation induced by mexiletine was less pronounced in arteries contracted with high KCl than in those contracted with noradrenaline. 6. Mexiletine induced identical relaxations in arteries contracted with noradrenaline in high KCl solution containing verapamil and in Krebs solution. 7. Thus, mexiletine induces relaxations by inhibiting transmembrane Ca2+ movement, but not Ca2+ release from the intracellular store site in mesenteric resistance arteries of rats. It is speculated that mexiletine possesses greater inhibitory effects against noradrenaline-activated, verapamil-insensitive (receptor-operated) Ca2+ channels than against verapamil-sensitive (voltage-dependent) channels.     

Noradrenaline-induced contraction of human saphenous vein and human internal mammary artery: involvement of different α-adrenoceptor subtypes

Although saphenous veins and internal mammary arteries are commonly used for coronary artery bypass grafting, only a very few comparative studies are available on alpha-adrenoceptor-mediated vasoconstriction in these vessels. Thus, we determined, in isolated rings from human saphenous vein and human internal mammary artery, contractile responses to noradrenaline (10(-8)-10(-4) M) in the absence and presence of the alpha-adrenoceptor antagonists yohimbine (alpha(2)-adrenoceptor antagonist, 10(-8)-10(-6) M), prazosin (alpha(1)-adrenoceptor antagonist, 10(-9)-10(-7) M), 5-methyl-urapidil (5-MU, alpha(1A)-adrenoceptor antagonist, 10(-8)-10(-6) M), BMY 7378 (alpha(1D)-adrenoceptor antagonist, 10(-7)-10(-6) M), and chloroethylclonidine (CEC, irreversible alpha(1B)-adrenoceptor antagonist, 3x10(-5) M for 30 min). All experiments were carried out in the presence of 10(-7) M propranolol and 10(-5) M cocaine. In both vessel types noradrenaline evoked concentration-dependent contractions. In saphenous veins yohimbine was a potent antagonist (pA(2)-value 8.32) while prazosin, 5-MU and BMY exhibited only marginal antagonistic effects. CEC, however, significantly decreased noradrenaline-induced contractions. In contrast, in internal mammary arteries prazosin (pA(2)-value 9.65) and 5-MU (pK(B)-values 7.2-7.5) were potent antagonists, while yohimbine and BMY exhibited only weak antagonistic effects. CEC, however, significantly decreased noradrenaline-induced contractions. We conclude that in saphenous vein the contractile response to noradrenaline is mediated predominantly by alpha(2)-adrenoceptors, while in internal mammary artery it is mediated (to a major part) by alpha(1B)- and (to a minor part) by alpha(1A)-adrenoceptors.     

Thapsigargin- and cyclopiazonic acid-induced endothelium-dependent hyperpolarization in rat mesenteric artery.

1. The present study was designed to determine whether putative, selective inhibitors of the Ca(2+)-pump ATPase of endoplasmic reticulum, thapsigargin (TSG) and cyclopiazonic acid (CPA), induce endothelium-dependent hyperpolarization in the rat isolated mesenteric artery. The membrane potentials of smooth muscle cells of main superior mesenteric arteries were measured by the microelectrode technique. 2. In tissues with endothelium, TSG (10(-8)-10(-5) M) caused sustained hyperpolarization in a concentration-dependent manner. In tissues without endothelium, TSG did not cause any change in membrane potential. CPA (10(-5) M) also hyperpolarized the smooth muscle membrane, an effect that was endothelium-dependent and long-lasting. 3. The hyperpolarizing responses to these agents were not affected by indomethacin or NG-nitro-L-arginine (L-NOARG). 4. In Ca(2+)-free medium, neither TSG nor CPA elicited hyperpolarization, in contrast to acetylcholine which generated a transient hyperpolarizing response. 5. In rings of mesenteric artery precontracted with phenylephrine, TSG and CPA produced endothelium-dependent relaxations. L-NOARG significantly inhibited the relaxations to these agents, but about 40-60% of the total relaxation was resistant to L-NOARG. The L-NOARG-resistant relaxations were abolished by potassium depolarization. 6. These results indicate that TSG and CPA can cause endothelium-dependent hyperpolarization in rat mesenteric artery possibly by releasing endothelium-derived hyperpolarizing factor and that membrane hyperpolarization can contribute to the endothelium-dependent relaxations to these agents. The mechanism of hyperpolarization may be related to increased Ca2+ influx into endothelial cells triggered by depletion of intracellular Ca2+ stores due to inhibition of endoplasmic reticulum Ca(2+)-pump ATPase activity.     

Proton pump inhibitors omeprazole and lansoprazole induce relaxation of isolated human arteries

Vasorelaxant effects of H+/K+-ATPase were previously demonstrated in artery rings isolated from experimental animals. We examined the effects of clinically used H+/K+-ATPase inhibitors on isolated human internal mammary (n=19) and radial (n=5) arteries. Omeprazole and lansoprazole (30-300 microM) both induced concentration-dependent, reversible and reproducible relaxations of arteries which were precontracted with phenylephrine (5 microM), histamine (15 microM), high K+ (80 mM), ouabain (1 microM) and K+ free solution. Relaxant responses were similar in both arteries. Presence of Nomega-Nitro-L-arginine methyl ester (30 microM) had no effect on lansoprazole-induced responses, thus relaxations are independent from nitric oxide. Relaxation in the K+ free medium implies that this action could not be due to the inhibition of H+/K+-ATPase. Lansoprazole (300 microM) inhibited Ca2+-induced contractions in high K+-Ca2+ free medium. Omeprazole and lansoprazole may act on a common mechanism which plays a crucial role in regulating human vascular tone and that mechanism appeared to be involved in the regulation of intracellular Ca2+.     

Endothelium modulates the effects of alpha-adrenoceptor agonists in vascular smooth muscle

1. The contraction induced by clonidine and guanfacine but not phenylephrine was enhanced in endothelium-denuded and methylene blue pretreated rabbit aortic, pulmonary artery rings and isolated perfused whole superior mesenteric, carotid and femoral arteries from the same species. 2. The responses to acetylcholine in guanfacine preconstricted superior mesenteric and carotid arteries were also augmented when compared with phenylephrine and clonidine preconstricted segments. No difference was observed to the relaxing activity of acetylcholine in the aortic, pulmonary artery rings and whole perfused femoral artery contracted by phenylephrine, clonidine and guanfacine. 3. Acetylcholine also produced a biphasic effects in the pulmonary artery rings precontracted with the used alpha-adrenoceptor agonists. The contractile effect was observed with the concentration up to 10(-6) M of acetylcholine and was higher for guanfacine than phenylephrine and clonidine precontracted rings. 4. These results were taken as an evidence for the specificity of alpha 2-adrenoceptor agonists on the production and release of EDRF from vascular endothelium and in this respect guanfacine seems to have higher potency than clonidine. 5. These results also indicate that production or release of EDRF from vascular endothelium may vary depending on the regional vascular bed.     

Upregulation of Rho-kinase (ROCK-2) expression and enhanced contraction to endothelin-1 in the mesenteric artery from lipopolysaccharide-treated rats

Effects of bacterial lipopolysaccharide (Escherichia coli serotype, 055:B5, 20 mg kg(-1), i.p., for 6 h) and a Rho-kinase inhibitor, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate, Y-27632 (10(-9)-10(-5) M) were investigated on the contractile responses of the rat mesenteric artery to phenylephrine (10(-9)-3 x 10(-5) M), angiotensin-2 (10(-10)-10(-6) M) and endothelin-1 (10(-10)-10(-7) M). Moreover, alteration in the level of Rho-kinase (ROCK-2) expression was examined in the superior mesenteric artery obtained from saline- and lipopolysaccharide-treated rats by Western blotting. Endotoxemic rat mesenteric rings exhibited no different contractions to phenylephrine and angiotensin-2 but augmented contractile activity to endothelin-1. In the mesenteric artery obtained from the endotoxemic rats, acetylcholine-induced vasorelaxation did not differ; pD2 value for acetylcholine was 7.85+/-0.12 in the endotoxemic rings; however, it was 7.81+/-0.15 in the control rings (P>0.05). Y-27632 induced relaxation, which was the same in the control arteries as in endotoxemic ones when contracting agent was phenylephrine. However, when endothelin-1 was used to precontract the rings, Y-27632 produced enhanced relaxation in endotoxemic vessels. pD2 values for Y-27632 were, respectively, 7.69+/-0.12 and 8.20+/-0.10 in control and endotoxemic rings precontracted by endothelin-1 (10(-8) M) (P<0.01). Moreover, Y-27632 (10(-5) M) suppressed the contraction induced by angiotensin-2 (10(-10)-10(-6) M). Western blot analysis revealed that Rho-kinase was upregulated significantly in the mesenteric artery obtained from the rats treated with LPS for 6 h. In addition, serum NO2-/NO3- level, which was detected by Griess method, was 10.0+/-1.4 microM in endotoxemic rats; however, it was 6.6+/-0.5 microM in control (P<0.05). Taken together, these results show that the expression of the contractile protein Rho-kinase could be upregulated in endotoxemic mesenteric artery and this upregulation may be coincided with an enhanced contraction to endothelin-1 but not phenylephrine and angiotensin-2.     

Nebivolol induces endothelium-dependent relaxations of canine coronary arteries.

Nebivolol is a new beta 1-antagonist that acutely reduces arterial blood pressure without depressing cardiac function. The present study was designed to determine the effect of nebivolol on coronary arteries. Rings of canine left anterior descending coronary (LAD) artery with or without endothelium were suspended in organ chambers and the isometric tension was recorded. In some experiments, the transmembrane potential of the smooth muscle cells was recorded by electrophysiological methods. During contractions to prostaglandin F2 alpha, nebivolol induced concentration-dependent relaxations of the coronary arteries. The enantiomer, l-nebivolol, also induced comparable relaxations; however, d-nebivolol induced smaller relaxations. The relaxations induced by nebivolol and its enantiomer were significantly larger in tissues with than in those without endothelium. The differences between tissues with and without endothelium were abolished by nitro-L-arginine (3 x 10(-5) M) or methylene blue (10(-5) M). The nebivolol-induced relaxations were not affected by indomethacin (10(-5) M), phentolamine (5 x 10(-6) M), propranolol (5 x 10(-6) M), or methysergide (3 x 10(-6) M). Nebivolol at a subthreshold concentration for inducing relaxation (3 x 10(-7) M) did not significantly affect endothelium-dependent relaxations to acetylcholine but potentiated ADP-induced endothelium-dependent relaxations. The potentiation is stereoselective for l-nebivolol. Nebivolol induced a small hyperpolarization of the coronary smooth muscle with endothelium (1 mV).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of resveratrol on nitrate tolerance in isolated human internal mammary artery

The present study aims to examine whether resveratrol, a natural antioxidant present in red wine, restores the tolerance to nitroglycerin (GTN) on isolated human internal mammary artery (IMA), using an in vitro model of nitrate tolerance. IMA rings were obtained from 53 male patients undergoing coronary bypass operation. Nitrate tolerance was induced by incubating the artery ring with 100 microM GTN for 90 minutes. Concentration-response curves to GTN (10(-9) to 10(-4) M) were obtained on IMA rings precontracted with noradrenaline. A low concentration (5 microM) of lucigenin was used as a tool to measure superoxide production in IMA segments. GTN produced concentration-dependent relaxation in isolated human IMA rings. Preexposure of artery rings to GTN reduced the relaxations to GTN [E(max) values: 105 +/- 2% and 76 +/- 3%, n = 10 to 12, P < 0.05; EC(50) values (-log M): 6.72 +/- 0.05 and 4.95 +/- 0.06, P < 0.05, respectively]. Relaxation to sodium nitroprusside remained unchanged. Diminished relaxation to GTN is partially restored after removing endothelium or L(G)-nitro-L-arginine (L-NOARG, 10 M) or superoxide dismutase (20 and 200 U/mL) or catalase (200 U/mL) pretreatments. Pretreatments with resveratrol (1, 10, and 20 microM) for 20 minutes relatively improved the reduced relaxation to GTN in tolerant IMA rings. Coadministration of L-NOARG with resveratrol did not abolish the beneficial effect of resveratrol on nitrate tolerance. The inhibitory effect of resveratrol on GTN-induced tolerance was not abolished in arterial rings without endothelium. Exposure to GTN increased superoxide production in IMA segments with endothelium. Endothelium denudation, L-NOARG, or superoxide dismutase pretreatments markedly inhibited the increased superoxide production in tolerant arteries. Resveratrol (1 and 10 microM) almost completely abolished basal or NAD(P)H-stimulated superoxide production in tolerant and nontolerant arteries. Vascular tolerance to GTN, in in vitro tolerant human IMA rings, can be induced by endothelial superoxide anions. Resveratrol partially restored the reduced relaxation to GTN by inhibiting NAD(P)-derived superoxide production in endothelium.     

Selective inhibition of basal but not agonist-stimulated activity of nitric oxide in rat aorta by NG-monomethyl-L-arginine.

1. Two inhibitors of nitric oxide synthase, NG-monomethyl-L-arginine (L-NMMA, 1-100 microM) and NG-nitro-L-arginine (L-NOARG, 3-300 microM), each produced a concentration-dependent augmentation of phenylephrine-induced tone in endothelium-containing but not endothelium-denuded rings of rat aorta. Pretreatment with L-arginine (10 mM) prevented the augmentation of tone induced by L-NOARG and L-NMMA. 2. Following induction of sub-maximal tone with phenylephrine in endothelium-containing rings, acetylcholine (1 nM-3 microM) induced relaxations which were inhibited in a concentration-dependent manner by L-NOARG (10-100 microM). 3. In contrast to the action of L-NOARG, L-NMMA (100-1000 microM) had no effect on acetylcholine-induced relaxations. L-NMMA (100-300 microM) also had no effect on the endothelium-dependent relaxant actions of ATP (0.1-100 microM), whereas L-NOARG (100 microM) produced powerful blockade. 4. Unexpectedly, pretreatment with L-NMMA (30-300 microM), as with the endogenous substrate L-arginine (10 microM-10 mM), inhibited in a concentration-dependent manner the ability of L-NOARG (30 microM) to block acetylcholine-induced relaxation. 5. The ability of L-NOARG to augment phenylephrine-induced tone and inhibit relaxation by acetylcholine and ATP in endothelium-containing rings is consistent with blockade of basal and agonist-stimulated production of nitric oxide, respectively. 6. The ability of L-NMMA to augment phenylephrine-induced tone without affecting relaxation to acetylcholine or ATP in endothelium-containing rings suggests a selective ability to block basal but not agonist-stimulated production of nitric oxide in rat aorta.     

Attenuation of vasoconstriction by endogenous nitric oxide in rat caudal artery.

1. The effects of NG-nitro-L-arginine (L-NNA), NG-nitro-L-arginine methyl ester (L-NAME), haemoglobin and methylene blue have been examined on vascular reactivity in the rat isolated caudal artery. The effects of L-NNA and sodium nitroprusside were also investigated on the stimulation-induced (S-I) efflux of noradrenaline in the rat caudal artery. 2. L-NNA (10 microM) and L-NAME (10 microM) significantly attenuated the vasodilator responses to acetylcholine (1 nM-1 microM), but had no effect on vasodilator responses to papaverine (1-100 microM). 3. Vasoconstrictor responses to sympathetic nerve stimulation (3 Hz, 10 s), noradrenaline (0.01-1 microM), methoxamine (1-10 microM), 5-hydroxytryptamine (0.01-0.3 microM), phenylephrine (0.1-10 microM), endothelin-1 (10 nM) and KCl (40 mM) were significantly enhanced by 10 microM L-NNA. L-NAME (10 microM) caused a significant enhancement of vasoconstrictor responses to noradrenaline and sympathetic nerve stimulation in endothelium-intact, but not in endothelium-denuded tissues. 4. Haemoglobin and methylene blue (both 10 microM) enhanced the vasoconstrictor responses to sympathetic nerve stimulation and noradrenaline. The enhancements were absent in endothelium-denuded arterial segments. 5. In endothelium-denuded arterial segments precontracted with phenylephrine, the vasodilator responses to the nitric oxide donor, sodium nitroprusside (0.1-300 nM) were decreased by increasing the level of precontraction. 6. L-NNA (10 microM) had no effect on the S-I efflux of radioactivity from arteries in which transmitter stores had been labelled with [3H]-noradrenaline.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulatory role of the vascular endothelium in the contractility of human isolated internal mammary artery

1. Endothelium-dependent relaxant responses and modulation of contractile responses were investigated in human isolated internal mammary artery (HIMA), a vessel widely used for coronary bypass surgery. 2. Acetylcholine and ionophore A23187 (both 10 nM-1 microM) elicited concentration-dependent relaxations of precontracted HIMA. These relaxations were abolished after rubbing of the endothelium, they were inhibited by methylene blue and were insensitive to indomethacin. 3. Histamine at concentrations lower than 10 microM elicited an endothelium-dependent, methylene blue-sensitive relaxation of precontracted HIMA. This effect of histamine was inhibited by the H1-receptor antagonist mepyramine. Bradykinin, noradrenaline and alpha 2-adrenoceptor agonists (in the presence of prazosin) did not relax unrubbed HIMA in which acetylcholine or A23187 were shown to be efficient. 4. Tissue levels of guanosine-3':5'-monophosphate (cyclic GMP) were found to be significantly higher in unrubbed HIMA rings than in matched rubbed rings. 5. Methylene blue evoked a slow contraction in resting HIMA, and this contraction was significantly greater in unrubbed than in rubbed preparations. Also, methylene blue enhanced the contractile response of HIMA to noradrenaline and this potentiating effect was significantly greater in unrubbed than in rubbed preparations. Indomethacin induced a slow contraction, of similar magnitude in unrubbed and rubbed HIMA rings. 6. In resting HIMA, the concentration-effect curve of noradrenaline-induced contraction was significantly shifted to the left after rubbing of the endothelium, without change in the maximal responses. In unrubbed rings the EC50 value of noradrenaline was about 2 fold that in rubbed rings. 7. Histamine also contracted resting HIMA in a concentration-dependent manner and in addition, it triggered rhythmic activity. This rhythmic activity was more prominent in unrubbed preparations and could be partially inhibited by indomethacin. The concentration-effect curve of histamine-induced contractions was displaced to the left after rubbing the endothelium, without changes in the maximal responses. The EC50 value of histamine in unrubbed rings was 4 to 9 fold that found in rubbed rings, depending on the level of tension taken into account for the concentration-effect curve during rhythmic contractions. 8. In the presence of nifedipine (3 microM), noradrenaline-induced contractions were not significantly altered, whereas histamine-induced contractions were found to be inhibited by about 70%.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cocaine-induced relaxation of isolated rat aortic rings and mechanisms of action: possible relation to cocaine-induced aortic dissection and hypotension

Cocaine HCl is well known for its toxic effects on the cardiovascular system, but little is known about its effects on different regional blood vessels. We designed experiments to determine if cocaine HCl could influence the tension of isolated aortic rings, i.e., induce contraction or relaxation. Surprisingly, cocaine HCl (1 x 10(-5) to 6 x 10(-3) M) relaxed isolated aortic rings precontracted by phenylephrine in a concentration-dependent manner. No significant differences were found between intact or denuded isolated aortic rings (P>0.05). The maximal % relaxations of intact vs. denuded isolated aortic rings were 108.9+/-24.3% vs. 99.5+/-8.3% (P>0.05). Cocaine HCl, 2 x 10(-3) M, was found to inhibit contractions by phenylephrine; EC50s were increased (P<0.01) and Emax's were decreased (51.3+/-16.4% vs. 89.8+/-10.6%, P<0.01). A variety of amine antagonists could not inhibit the relaxant effects of cocaine HCl (P>0.05). The cyclooxygenase-1 inhibitor, indomethacin, also failed to inhibit relaxations induced by cocaine HCl (P>0.05). Neither L-arginine, NG-monomethyl-L-arginine (L-NMMA), nor methylene blue could inhibit the relaxations induced by cocaine HCl (P>0.05), suggesting cocaine HCl does not relax isolated aortic rings by inducing the synthesis or release of nitric oxide (NO) or prostanoids from either endothelial or vascular muscle cells. Inhibitors of cAMP, cGMP and protein kinase G (PKG) also failed to inhibit cocaine-induced relaxations. Cocaine HCl (1 x 10(-5) to 6 x 10(-3) M) could also relax isolated aortic rings precontracted by phenylephrine in high K+ depolarizing buffer. Surprisingly, calyculin A, an inhibitor of myosin light chain (MLC) phosphatase, inhibited cocaine-induced relaxations in a concentration-dependent manner, suggesting the probable importance of cocaine-induced MLC phosphatase activation in rat aortic smooth muscle cells. It was also found that cocaine HCl could dose-dependently inhibit Ca2+-induced contractions of isolated aortic rings in high K+-Ca2+-free buffer, suggesting that cocaine HCl may inhibit Ca2+ influx and/or intracellular release.     

Unfractioned heparin produces vasodilatory action on human internal mammary artery by endothelium-dependent mechanisms

The aim of this study was to investigate whether unfractioned heparin produces a direct vasodilatory effect on the human internal mammary artery (IMA) and the possible underlying mechanisms. Samples of redundant IMA were obtained from 20 patients undergoing coronary artery bypass graft surgery, and concentration-response curves to unfractioned heparin were constructed. Unfractioned heparin (0.5-6 U/mL) caused a concentration-dependent relaxation in the endothelium-intact human IMA rings precontracted with phenylephrine (10(-6) M). Removal of endothelium significantly inhibited the responses of human IMA to unfractioned heparin (P < 0.05). Nomega-Nitro-L-arginine methyl ester (L-NAME, 10(-4) M), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10(-5) M) and L-NAME (10(-4) M) plus ODQ (10(-5) M) partially reduced unfractioned heparin-induced vasodilatory response in endothelium-intact rings, whereas indomethacin alone had no effect. The vasodilatory effect of unfractioned heparin was completely inhibited by 40 mM KCl in the presence of L-NAME, ODQ, and indomethacin. These results clearly demonstrated that unfractioned heparin causes a concentration-dependent vasodilatation in human internal mammary artery, and this action seems to be via endothelium-dependent mechanisms, including generation of nitric oxide and endothelium-derived hyperpolarizing factor.     

Effects of deferoxamine and sympathectomy on endothelin-1-induced contraction and acetylcholine—Induced relaxation following subarachnoid hemorrhage in carotid artery

The role of endothelium-related factors in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH) has gained interest since the discovery of EDRF and of endothelin-1 (ET-1). The effect of SAH and both treatment of deferoxamine (DFO) and sympathectomy on endothelium-dependent vasodilation and ET-1-induced vasoconstriction of isolated rabbit carotid artery was examined using an isometric tension recording method. Thirty-five rabbits were divided into four groups: control animals, 7 days after SAH, treatment with DFO after SAH for 7 days and sympathectomy after SAH. Acetylcholine (10⁻⁸ to 10⁻⁵ M) was used to evoke concentration-dependent vasodilation of isolated arterial rings previously contracted by 10⁻⁶ M phenylephrine. In the animals killed 7 days after SAH, acetylcholine-induced relaxation was suppressed and the degree of relaxation of this group was 50% of the initial contractile tone in response to the 10⁻⁵ M acetylcholine. These relaxant responses did not return to control values in carotid arteries obtained from animals treated with DFO and subjected to sympathectomy. In isolated carotid arteries, ET-1 (10⁻¹⁰ to 10⁻⁸ M) produced concentration-dependent contractions. These contractile responses were significantly enhanced in animals 7 days after SAH compared with controls and did not return to control values in carotid arteries obtained from animals both treated with DFO and sympathectomized for 7 days after SAH. The present experiments suggest that impairment of endothelium-dependent vasodilation and the hyperreactivity of ET-1 of the carotid artery as well as cerebral arteries may be involved in the pathogenesis of cerebral vasospasm. Both treatment with DFO and sympathectomy during the chronic stage for vasospasm after SAH did not affect these vascular responses of the extradural part of the carotid artery to ET-1 and acetylcholine.     

Contractile and relaxant responses of the canine isolated spinal artery to vasoactive substances.

1. Effects of vasoactive substances were investigated in the canine isolated spinal branch of the intercostal artery (SBICA). 2. Addition of angiotensin II (AII), vasopressin, noradrenaline (NA), adrenaline, 5-hydroxytryptamine (5-HT), and dopamine each produced concentration-dependent contraction in the SBICA, whereas prostaglandin F2 alpha, histamine, and tyramine caused only slight contraction. The decreasing order of the potency of contractile agents was AII much greater than vasopressin = NA greater than 5-HT greater than adrenaline much greater than dopamine. 3. Although the pD2 value for phenylephrine (5.31 +/- 0.36) was smaller than that for NA (6.48 +/- 0.13), there was no significant difference in Emax value between these two agonists in the SBICA. On the other hand, xylazine produced only a slight contraction, the pD2 value being 3.59 +/- 0.08. Phentolamine (10(-8)-10(-6) M) and prazosin (10(-8)-10(-6) M) competitively inhibited the NA-induced contraction, while yohimbine (10(-8)-10(-6) M) did not. 4. Acetylcholine (ACh), sodium nitroprusside (SNP), ATP, ADP, and adenosine caused concentration-dependent relaxations in SBICA following contraction with NA. On the other hand, isoprenaline up to 10(-4) M did not produce any relaxation. The decreasing order of potency of the relaxant agents was ACh greater than SNP much greater than ATP = ADP = adenosine. 5. The ACh-induced relaxation was competitively inhibited by atropine and was abolished by mechanical removal of the endothelium. Aspirin (5 x 10(-5) M) did not affect the relaxant response to ACh, while oxyhaemoglobin (10(-5) M) and methylene blue (10(-5) M) produced significant attenuation.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Feline Carotid Rete: Vasomotor Reactivity of Isolated Arteries

Abstract: Vasomotor responses of arteries from the feline carotid rete were examined using a sensitive in vitro system. The vessel segments constricted in response to several vasoactive agents and putative neurotransmitters. Sympathomimetic agents (noradrenaline, adrenaline, oxymetazoline, phenylephrine), 5-hydroxytryptamine, histamine, angiotensin II, and prostaglandin F_2α all induced concentration-dependent contractile responses. The contractions induced by noradrenaline, 5-hydroxytryptamine, and histamine could be antagonized by phentolamine, methysergide, and mepyramine, respectively. Cholinomimetics (acetylcholine, carbacholine), vasoactive intestinal peptide and papaverine induced potent dilatory responses. The effect of carbacholine was shifted towards higher agonist concentrations by atropine. Dilatations, though small in magnitude, were found by application of adenosine, isoproterenol, and histamine. These results correlate well with the recent demonstration of autonomic nerves and indicate the occurrence of corresponding receptor sites in the walls of the carotid rete arteries.     

P2-purinoceptors mediate both vasodilation (via the endothelium) and vasoconstriction of the isolated rat femoral artery

The distribution of P1- and P2-purinoceptors in isolated rat femoral artery was studied by comparing responses to ATP, alpha, beta-methylene ATP and adenosine, both when endothelial cells were intact and when they had been removed by mechanical rubbing (as confirmed by histochemical staining and abolition of relaxations to acetylcholine). alpha, beta-Methylene ATP and ATP (but not adenosine or acetylcholine) contracted preparations at resting tone. alpha, beta-Methylene ATP was significantly more potent than ATP. The potency of both alpha, beta-methylene ATP and ATP was significantly increased in the absence of the endothelium. These contractions were unaffected by tetrodotoxin, phentolamine and methysergide in concentrations sufficient to abolish contractions to perivascular nerve stimulation, noradrenaline or 5-hydroxytryptamine. Acetylcholine, ATP and adenosine relaxed arteries whose tone had been raised by 10(-6) M noradrenaline. Removal of the endothelium abolished relaxations to ATP (contractions were seen instead) and acetylcholine, but not to adenosine. alpha, beta-Methylene ATP further contracted the high tone preparation and was again more potent when the endothelium was absent. ATP and alpha, beta-methylene ATP were more potent as contractile agents when noradrenaline was present. These results confirm that endothelial cells can mediate vasodilation. They also show that ATP can act at P2-purinoceptors at two locations in the isolated rat femoral artery; one on the endothelium leading to vasodilation, and the other on the smooth muscle leading to vasoconstriction. P1-Purinoceptors, however, appear to be located on the smooth muscle only and mediate vasodilation. At the smooth muscle P2-purinoceptor, alpha, beta-methylene ATP is more potent than ATP, whereas at the endothelial P2-purinoceptor, the reverse is true.     

Effect of dietary vitamin E supplementation on vascular reactivity of thoracic aorta in streptozotocin-diabetic rats

The present study evaluated the effect of dietary vitamin E supplementation (1,000 mg/kg chow) on the alterations in vascular reactivity of streptozotocin-diabetic aorta of Wistar rats. After 12 weeks of treatment, thoracic aortic rings of rats were mounted in organ baths and contractile responses to phenylephrine and 5-hydroxytryptamine and relaxant responses to acetylcholine, calcium ionophore and sodium nitroprusside were assessed. Plasma vitamin E concentration as measured by HPLC was markedly decreased in diabetic rats and increased with dietary vitamin E supplementation. Induction of diabetes significantly impaired endothelium-dependent relaxations to acetylcholine and calcium ionophore in aortic rings, but did not change endothelium-independent relaxation to sodium nitroprusside. Vitamin E significantly improved the impaired endothelium-dependent relaxations, further it decreased the enhanced contractile response to phenylephrine and 5-hydroxytryptamine in diabetic rings. The mechanical denudation of endothelium or the chemical inhibition of endothelium-dependent relaxation with N(omega)-nitro-L-arginine methyl ester (100 micromol/l) significantly increased phenylephrine contractility in control rings and the rings of diabetic rats treated with vitamin E; such a difference was not observed in diabetic rats fed with normal diet. Liver and lung malondialdehyde concentrations, as an index of lipid peroxidation, were increased in diabetic rats and significantly decreased with vitamin E supplementation. It is concluded that dietary supplementation of vitamin E improved endothelial dysfunction in insulin-dependent model of uncontrolled diabetes, probably decreasing membranal lipid peroxidation.     

Effect of ranolazine on rat intrarenal arteries in vitro

Ranolazine is mainly used to treat patients with chronic stable angina in clinical practice. However, ranolazine does not lower significantly systemic blood pressure. The direct effect of ranolazine on vascular tone remains unknown. In the present study, we investigated the vascular effects and mechanisms of action of ranolazine in isolated rat intrarenal arteries. Rings of intrarenal arteries were mounted in a small vessel myography using two stainless steel wires for the measurement of isometric tension. L-type Ca2? currents were recorded in isolated single renal arterial smooth muscle cells using patch clamp techniques in whole-cell mode. Ranolazine induced concentration-dependent relaxations in rings contracted with phenylephrine, but ranolazine failed to cause any relaxation in rings pre-contracted by U46619, 5-HT or endothelin-1. Ranolazine also induced relaxations in norepinephrine pre-contracted rings. Yohimbine failed to induce relaxation in rings pre-contracted by norepinephrine. Propranolol did not affect ranolazine-induced relaxation but the relaxant effect of ranolazine was much less than that of prazosin. Ranolazine-induced relaxations were slight but significantly attenuated by endothelial denudation. Partial inhibition was observed in endothelium-intact arteries exposed to a combination of iberiotoxin and apamin. Ranolazine at higher concentration (>30 μM) inhibited Ca2?-induced contraction in a noncompetitive manner. Ranolazine reduced L-type Ca2? currents at potentials between -30 and 50 mV in isolated renal artery myocytes. Therefore it can be said that ranolazine has significant α?-adrenergic receptor and weak calcium channel antagonistic effects in rat intrarenal arteries.