Regulation Of Coronary Artery Tone Research Articles

Differences in vascular reactivity to soluble guanylate cyclase agonists between female and castrated male pigs

This study investigated whether there are sex differences in vasorelaxation through the nitric oxide (NO)/soluble guanylate cyclase (sGC) pathway. The hearts of female (F) and castrated male (CM) pigs (6-month-old) were collected at a local abattoir, and left anterior descending coronary arteries were isolated to perform organ chamber experiments. Vasorelaxant activity was assessed based on the pD2 values. Bradykinin induced a concentration-dependent relaxation, which was comparable between F [8.55±0.13] and CM [8.67±0.11]. In the presence of L-NAME (100 μM, NO synthase inhibitor), the response to bradykinin was attenuated similarly in F [7.27±0.24] and CM [7.42±0.29]. Sodium nitroprusside (SNP, reduced sGC agonist) also induced relaxation in a concentration-dependent manner, and the potency in F [6.54±0.12] was similar to that in CM [6.50±0.11]. Pretreatment with ODQ (10 μM, sGC heme oxidant) attenuated SNP-induced relaxation similarly in F [4.77±0.19] and CM [4.78±0.09]. Likewise, there were no differences in BAY 60-2770 (oxidized/apo sGC agonist)-induced relaxation irrespective of the presence [10.64±0.20 (F) vs. 10.47±0.14 (CM)] or absence [9.89±0.11 (F) vs. 9.67±0.15 (CM)] of ODQ. These findings suggest that there are no differences in the regulation of coronary artery tone in response to sGC agonists between F and CM.

Features of endothelial function and autonomic regulation of heart rhytm in patients with vasospastic angina

BACKGROUND: The clinical features of vasospastic angina are well known, but pathogenesis remains a subject of discussion. Changes in the autonomic regulation of coronary artery tone and endothelial function that contribute to the development of vasospasm are not well understood. The data on the subject from the published studies are contradictory.
 AIM: To evaluate features of endothelial function and autonomic regulation of heart rhythm in patients with vasospastic angina.
 MATERIALS AND METHODS: The study included 16 patients with proven vasospastic angina. All the patients have been evaluated for the heart rate variability at rest and vegetative tests (deep breathing, and active standing tests). Endothelial function has been assessed in terms of reactive hyperemia index by peripheral arterial tonometry using an Endo-PAT 2000 device.
 RESULTS: The baseline of the total heart rate variability was borderline with the normal parameters SDNN 50 (32.5; 50) ms in the patients with vasospastic angina. There were 14 patients who have demonstrated an imbalance of the autonomic nervous system at rest, mainly due to an increase of parasympathetic influences. The appropriate reaction of the autonomic nervous system, characterized by an increase of vagal influences, has been determined in 13 patients in the deep-breathing test. A paradoxical reaction, characterized by an increase of vagal influences on the heart rhythm, has been registered in 13 patients in the active standing tests. Endothelial dysfunction has been observed in half of the studied patients. Furthermore, a combination of both pathophysiological mechanisms, i.e., endothelial and autonomic dysfunctions have been observed in all the patients with a reduced reactive hyperemia index.
 CONCLUSIONS: According to the results of our study, the parasympathetic influences of the autonomic nervous system on the heart rhythm were predominant in the patients with vasospastic angina, which is not typical for coronary heart disease. All the patients had autonomic or endothelial dysfunction. A combination of both pathophysiological mechanisms has been observed in half of the examined patients.

Sex differences in the regulation of porcine coronary artery tone by perivascular adipose tissue: a role of adiponectin?

As there is sexual dimorphism in the regulation of vascular tone, the aim of this present study was to determine whether there are sex differences in perivascular adipose tissue (PVAT)-mediated regulation of the porcine coronary artery (PCA) tone. Isometric tension recording system was used to record changes in tone in PCAs. Western blot analysis was performed to examine the expression of adiponectin in PVAT and adiponectin receptors and adiponectin binding protein (APPL1) in PCA. The level of adiponectin released from PVAT was measured using elisa. In the presence of adherent PVAT, contractions to the thromboxane mimetic U46619 and endothelin-1 were significantly reduced in PCAs from females, but not males. In PCAs pre-contracted with U46619, re-addition of PVAT caused relaxation in PCAs from females, but not males. This relaxant response in females was attenuated by combined inhibition of NOS (with L-NAME) and COX (with indomethacin). Pre-incubation with an anti-adiponectin antibody abolished the relaxant effects of PVAT. The adiponectin receptor agonist (adipoRon) produced a greater relaxation in PCAs from females compared with males. However, there was no difference in either the expression or release of adiponectin from PVAT between sexes. Similarly, there was no difference in the expression of adiponectin receptors or the adiponectin receptor adaptor protein APPL1 in PCAs. These findings demonstrate a clear sex difference in the regulation of coronary arterial tone in response to adiponectin receptor stimulation, which may underlie the anticontractile effects of PVAT in females.

The synthesis of 20-HETE in small porcine coronary arteries antagonizes EDHF-mediated relaxation

Exogenous application of 20-hydroxyeicosatetraenoic acid (20-HETE) to small (300-500 microm) porcine coronary arteries elicits contraction by activating the Rho kinase and increasing the sensitivity of contractile proteins to Ca2+. Here, we determined whether 20-HETE is involved in the regulation of coronary artery tone as well as its role in the modulation of endothelium-derived hyperpolarizing factor (EDHF)-mediated responses. Small porcine coronary arteries expressed cytochrome P450 (CYP) 4A, as demonstrated by Western blot analysis, and generated 20-HETE. Moreover, 20-HETE production was increased two- and threefold over basal levels in response to isometric stretch or the thromboxane analogue U46619, respectively, and was inhibited by the CYP 4A inhibitor N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS). In vascular reactivity studies, DDMS attenuated U46619-induced contractions and induced a concentration-dependent but endothelium-independent relaxation of precontracted arterial rings. Endogenously generated 20-HETE significantly inhibited the EDHF-mediated relaxation of coronary arteries, which was potentiated by the phospholipase A2 inhibitors AACOCF3 and ONO-RS-082, as well as by the omega-hydroxylase inhibitors 17-octadecynoic acid and DDMS. EDHF-mediated relaxation was not affected by either the nonselective epoxygenase inhibitors miconazole and clotrimazole or the CYP 2C inhibitor sulfaphenazole but was abolished by the Na-K-ATPase inhibitor, ouabain. Exogenous application of 20-HETE inhibited EDHF-mediated relaxations and caused a concomitant increase in the phosphorylation of protein kinase Calpha (PKCalpha). This effect was reversed by the PKC inhibitor Ro-318220 and mimicked by the PKC activator phorbol-12 myristate 13-acetate. These results indicate that vascular tone in small porcine coronary arteries is partly determined by the endogenous production of 20-HETE. In addition, 20-HETE functionally antagonizes EDHF-mediated relaxation via a PKCalpha-dependent mechanism, probably involving the inhibition of the Na-K-ATPase.

Endothelial COX-2 inhibition

Endothelial COX-2 inhibition

BK(Ca) channels compensate for loss of NOS-dependent coronary artery relaxation in cardiomyopathy.

Previously, we showed that development of myocardial necrotic lesions is associated with impaired endothelium-dependent coronary artery relaxation in young cardiomyopathic hamsters. Since active necrosis declines with aging, this study was designed to determine whether coronary artery endothelium-dependent relaxation to ACh is restored and to identify the mechanisms mediating this effect. Intraluminal diameter was recorded in coronary arteries (150-250 micrometer) from control (C, 297 +/- 5 days old) and cardiomyopathic (M, 296 +/- 4 days old) hamsters. Relaxation to ACh (10(-9)-3 x 10(-5) M) was similar in vessels from C and M hamsters. However, mechanisms mediating relaxation to ACh were altered. Inhibition of nitric oxide synthase (NOS) activity with N-nitro-L-arginine (1 mM) had a greater inhibitory effect in vessels from C hamsters, indicating a reduction in NOS-dependent relaxation in vessels from M hamsters. Conversely, inhibition of large Ca(2+)-dependent K(+) (BK(Ca)) channels with charybdotoxin (CTX, 0.1 microM) had a greater inhibitory effect in vessels from M hamsters. In the presence of both N-nitro-L-arginine and CTX, relaxation to ACh was abolished in both groups. CTX (0.1 micrometer) produced a 50 +/- 4 and 30 +/- 3% contraction of vessels from M and C hamsters, respectively, indicating an enhanced role for BK(Ca) channels in regulation of coronary artery tone in M hamsters. Finally, vasodilatory cyclooxygenase products contributed to ACh-induced relaxation in vessels from M, but not C, hamsters. In conclusion, NOS-dependent relaxation of coronary small arteries is reduced in the late stage of cardiomyopathy. An increase in relaxation mediated by BK(Ca) channels and vasodilatory cyclooxygenase products compensates for this effect.

Endothelial and myogenic regulation of coronary artery tone in the mouse

Ventricular septal (150–200 μm) arteries were isolated from the hearts of six-week-old CD-1 mice and mounted on a pressure myograph. Equilibration of the vessels at 70 mm Hg for 60 min resulted in the development of spontaneous myogenic tone. Maximum tone observed in these vessels greatly exceeded that previously reported in septal arteries from rats. Inhibition of endothelin ET A and endothelin ET B receptors with bosentan (1 and 10 μM) reduced basal tone. Endothelin release required intact endothelial cells. The α 1-adrenceptor selective agonists phenylephrine and methoxamine did not cause change in coronary tone, while the α 2-adrenceptor selective agonists 6-allyl-2-amino5,6,7,8-tetrahydro-4 H-thiazolo-[4,5-d]azepin-dihydrochloride (BHT 920) and clonidine produced vasodilatation. Noradrenaline (1 nM–10 μM) induced a concentration-dependent vasodilatation, which was inhibited by concurrent treatment with yohimbine (10 μM) and propranolol (20 μM). Vasodilatation due to BHT 920 was abolished with vessel denudation, indicating the endothelial location of α 2-adrenoceptors. Acetylcholine (1 nM–10 μM) caused an endothelium dependent vasodilatation; inhibition of nitric oxide synthase with N ω-nitro- l-arginine methyl ester attenuated this response. The endothelium-dependent vasodilators bradykinin and substance P produced no vasomotor effect in mouse coronary arteries. Differences between human and murine responses may impact on the relevance of the mouse coronary artery for use as a potential model of human coronary vessel diseases.

Deficiency in nitric oxide bioactivity in epicardial coronary arteries of cigarette smokers

This study sought to examine nitric oxide-mediated regulation of epicardial coronary arterial tone in cigarette smokers. Cigarette smoking is a major risk factor for coronary artery disease and is highly prevalent in patients with coronary spastic angina. Long-term exposure to cigarette smoking has been recently reported to suppress endothelium-dependent arterial relaxation in vivo humans. Responses of epicardial coronary artery diameter to single or combined infusion of acetylcholine and NG-monomethyl-L-arginine (L-NMMA) into the left main coronary artery were examined in 11 current smokers and 17 nonsmokers using quantitative coronary angiography. Acetylcholine dilated one-third of the proximal segments and most of the distal segments of coronary arteries in nonsmokers, whereas it constricted most of the proximal and distal segments in smokers. L-NMMA decreased the basal diameter of coronary arteries in nonsmokers but had minimal effect on the basal diameter in smokers. L-NMMA abolished the dilator response to acetylcholine in the coronary arteries of nonsmokers but had minimal effect on the constrictor response to acetylcholine in the arteries of smokers. The dilator response to nitroglycerin was significantly increased in the coronary arteries of smokers compared with in those of nonsmokers. The constrictor response to L-NMMA at rest was significantly correlated with the dilator response to nitroglycerin and with the diameter changes to acetylcholine in both smokers and nonsmokers. Nitric oxide bioactivity at rest and at acetylcholine-stimulated conditions in smokers was decreased, leading to the supersensitivity of the artery to the dilator effect of nitroglycerin as well as the constrictor effect of acetylcholine in smokers. Cigarette smoking affects nitric oxide-mediated regulation of coronary artery tone.

Effect of vasoactive intestinal peptide and the distribution of receptors in human epicardial coronary arteries

Background The aim of this study was to elucidate a possible role for vasoactive intestinal peptide (VIP) in the regulation of coronary vascular tone. Its action and the distribution of [125I]-VIP binding sites were examined in isolated human coronary arteries. Methods A total of 97 segments were obtained from 23 patients undergoing cardiac transplantation. Results VIP (10−10 to 3 × 10−7 M) relaxed preconstricted coronary segments in a concentration-dependent manner, with a maximum response of 73.8% ± 8.5% of the maximum relaxation induced by 1 μg/mL of nitroglycerin. This action was inhibited by the specific receptor antagonist [4CI-D-Phe6, Leu17] VIP, with a reduction of the maximum effect from 73.8% ± 8.5% to 38.9% ± 5.4% (P < 0.001). Prior exposure to atropine and indomethacin, and removal of the endothelium had no effect on responses to VIP. Receptor autoradiography demonstrated that [125I]-VIP binding sites were displaced by unlabeled peptide and by [4CI-D-Phe6, Leu17] VIP in a concentration-dependent manner, with 50% inhibitory concentration values of 1.35 × 10−8 and 2.41 × 10−8 M, respectively. The binding was predominantly associated with smooth muscle and perivascular regions, with no binding to the endothelial cells. Conclusions Our results indicate that VIP elicits vasodilatation of the human coronary artery by acting mainly on specific receptors presumably present on the smooth muscle. This peptidergic control mechanism may play a role in the regulation of coronary artery tone.

Endothelium determines flow-dependent dilation of the epicardial coronary artery in dogs

The mechanisms of epicardial coronary artery dilation alter reactive hyperemia were studied in instrumented conscious dogs. A pair of ultrasonic crystals, an electromagnetic flow probe and a cuff occluder were placed on the left circumflex coronary artery in 12 mongrel dogs under sterile conditions. Reactive hyperemia after 20 s of coronary occlusion dilated the epicardial coronary artery by 120 ± 14 μm (3.8 ± 0.6%, p < 0.01) from 3.167 ± 0.345 mm. This reactive dilation was abolished by flow-limiting coronary stenosis. However, vasodilation after nitroglycerin was 168 ± 26 μm (5.1 ± 0.5%) and 162 ± 27 μm (4.9 ± 0.6%), respectively, before and after flow limitation.After removal of the endothelium by a balloon catheter, dilation of the epicardial coronary artery after reactive hyperemia was markedly attenuated to 7 ± 4 μm (p < 0.01 versus before denudation), despite the presence of a similar degree of reactive hyperemia. The extent of coronary dilation after nitroglycerin was unchanged before and after de-endothelialization. Thus, the endothelium contributed to reactive dilation but not to the nitroglycerin-induced dilation. The negative feedback control of coronary diameter to changes in flow velocity may relate to the regulation of coronary artery tone.

Calcitonin gene-related peptide (CGRP) is a potent non-endothelium-dependent inhibitor of coronary vasomotor tone.

1 Ring segments of bovine left circumflex coronary artery were pre-contracted with 5-hydroxytryptamine or phenylephrine and then exposed to increasing concentrations of calcitonin gene-related peptide (CGRP) and other drugs. 2 CGRP administration resulted in dose-dependent inhibition of induced tone. Maximal relaxation to CGRP was 89 +/- 5% and the concentration required to achieve 50% maximal relaxation (EC50) was 2.11 +/- 1.35 X 10(-9)M. 3 CGRP-induced relaxation was not affected by removal of endothelial cells nor was it significantly altered by incubation of coronary vessels with atropine, propranolol, phentolamine (all 10(-6)M) or indomethacin (10(-5)M). 4 From these data we conclude that CGRP is a potent inhibitor of coronary artery vasomotor tone which appears to act directly on vascular smooth muscle rather than through the release of a secondary mediator. These data support the possibility that CGRP may play a role in non-adrenergic, non-cholinergic regulation of coronary artery tone.

Regulation of coronary artery tone in relation to the activation of signal transductors that regulate calcium homeostasis

Muscle tone of coronary arteries is regulated by free calcium concentration in the myoplasm. Various agonists, autacoids and putative peptides modify the calcium concentration directly or through actions of second messengers (signal transductors), such as cyclic guanosine monophosphate (GMP), cyclic adenosine monophosphate (AMP), inositol 1,4,5-trisphosphate, diacylglycerol or calmodulin. For example, acetylcholine (in the presence of intact endothelium cells), alpha-human natriuretic peptide or nitrate compounds increase the amount of cyclic GMP and isoproterenol, prostacyclin (prostaglandin I2) or vasoactive intestinal polypeptide increases cyclic AMP. Both cyclic nucleotides reduce free calcium concentration. On the other hand, acetylcholine (in the presence or absence of endothelium cells), norepinephrine or thromboxane A2 increases inositol 1,4,5-trisphosphate and diacylglycerol, thus causing the increase in the free calcium concentration, whereas vasoactive intestinal peptide and alpha-human natriuretic peptide reduce them. Calmodulin acts as an internal calcium receptor for regulation of the contractile machinary. Regulation of calcium homeostasis in relation to the muscle tone in the coronary arteries including other vascular tissues is discussed together with the role of second messengers.