Vasorelaxant properties of isolated human radial arteries: comparison with internal mammary arteries

Effects of Nicorandil Versus Nitroglycerin on Arterial Oxygenation During Two-Lung Ventilation and One-Lung Ventilation in Patients With Risk Factors for Myocardial Ischemia: A Prospective, Randomized, Double-Blind Study

OBJECTIVES

To compare the effects of nicorandil and nitroglycerin on arterial oxygenation during two-lung ventilation (TLV) and one-lung ventilation (OLV) in patients with risk factors for myocardial ischemia.

DESIGN

A prospective, randomized, double-blind study.

SETTING

A tertiary care hospital.

PARTICIPANTS

Fifty-six patients scheduled for elective video-assisted thoracic surgery were assigned randomly to either the nicorandil group or the nitroglycerin group.

INTERVENTIONS

Patients in the nicorandil group received a bolus dose of nicorandil, 0.08 mg/kg during induction of anesthesia, followed by a continuous infusion at a rate of 0.08 mg/kg/h. Patients in the nitroglycerin group received a continuous infusion of nitroglycerin at a rate of 1 µg/kg/min from the induction of anesthesia.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gas analysis was performed at the following points: before induction of anesthesia; during TLV; at 5, 10, 20, and 30 minutes after the initiation of OLV. PaO₂ at TLV (479.7 ± 57.1 v 408.2 ± 70.9 mmHg, p < 0.001); and at 5 minutes (344.8 ± 85.1 v 282.6 ± 85.8 mmHg, p = 0.012), 20 minutes (215.7 ± 103.0 v 158.2 ± 74.5 mmHg, p = 0.027), and 30 minutes (198.8 ± 103.5 v 147.5 ± 64.1 mmHg, p = 0.039) after OLV was significantly higher in the nicorandil group than in the nitroglycerin group.

CONCLUSION

This study demonstrated that oxygenation during TLV and OLV was significantly higher in patients receiving nicorandil than in those receiving nitroglycerin.

Relaxant effect of the prostacyclin analogue iloprost on isolated human radial artery: An approach for the reversal of graft spasm

Radial artery graft spasm in the perioperative or postoperative period of coronary bypass surgery necessitates urgent treatment due to risk of graft failure and mortality. Herein, we evaluated the effect of iloprost, a prostacyclin (PGI₂) analogue, against the contractions produced by noradrenaline and potassium chloride on isolated human radial artery. Following the determination of endothelial and vascular relaxing capacities of the arteries, iloprost (10^-9M-10^-6M) was cumulatively applied on rings precontracted submaximally with the spasmogens. In some rings, the response to iloprost was assessed following pretreatment with nitric oxide (NO) synthase inhibitor, l-NAME (3×10^-4M,30min). Iloprost produced complete relaxations on radial artery rings precontracted with noradrenaline whereas, only moderate relaxations against the contractions induced by potassium chloride. Notably, the relaxation to iloprost was remarkably blunted in radial arteries with impaired endothelial function. Moreover, the relaxation to iloprost was unchanged in rings pretreated with l-NAME. Our results demonstrated that iloprost could be a potent relaxant agent in reversing radial artery spasm, particularly initiated by noradrenaline, possibly acting via an endothelium-mediated mechanism unrelated to NO.

Different expression of large-conductance calcium-activated K+ channels in human internal mammary and radial arteries

AIMS

In this study, we investigated and compared the electrophysiological and molecular properties of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels between human internal mammary arteries (IMA) and radial arteries (RA).

METHODS AND RESULTS

IMA and RA sections were obtained from 79 patients (including 9 females) undergoing coronary artery bypass graft surgery. We examined the effects of K(+) channel blockers tetraethylammonium (TEA), iberiotoxin (IBTX), and 4-aminopyridine (4-AP) on isolated smooth muscle cells (SMCs) using patch clamping. Both TEA (1 mM) and IBTX (0.1 µM) significantly decreased K(+) currents in IMA SMCs and RA SMCs, while 4-AP (1 mM) only had a weak effect. IBTX had a greater K(+)-blocking effect on IMA SMCs than on RA SMCs. Consistently, TEA and IBTX evoked significant constriction of both intact vascular rings. IBTX had a greater constrictor effect on IMA rings (18.5 ± 6.7%, n= 8) than on RA rings (10.6 ± 3.1%, n= 8), P< 0.05. RT-PCR and western blot analysis demonstrated that gene and protein expression of the α-subunit of BK(Ca) channels from IMA was greater than that from RA.

CONCLUSION

The density of BK(Ca) channels is greater in human IMA than in RA resulting in greater BK(Ca) currents in SMCs from IMA. This may partly explain the finding of less spasm in IMA grafts than in RA grafts. Our results may be of value in determining the best anti-spasm agent to use peri-operatively.

Modulation of noradrenergic neurotransmission in isolated rat radial artery

The present study was designed to characterize the neurogenic contraction of rat radial artery. Electrical field stimulation (EFS) evoked frequency-dependent contraction that was abolished by tetrodotoxin (neuronal Na(+) channel blocker), guanethidine (sympathetic neuron blocker), or phentolamine (alpha-adrenoceptor blocker). The alpha(1)-adrenoceptor antagonist prazosin inhibited endothelium-independent contractions to EFS, noradrenaline (NA), and the alpha(1)-adrenoceptor agonist phenylephrine. Rauwolscine, an alpha(2)-adrenoceptor antagonist, augmented nerve-mediated contractions and reduced sensitivity to NA and the alpha(2)-adrenoceptor agonist BHT-920. The beta-adrenoceptor antagonist propranolol diminished EFS-elicited contractions, while sensitivity to NA was enhanced by propranolol. Relaxations evoked by isoproterenol, a beta-adrenoceptor agonist, were abolished by propranolol. N(G)-Nitro-L-arginine (L-NOARG), a nitric oxide (NO) synthase inhibitor, increased both nerve-mediated and NA-induced responses in endothelium-intact, but not in endothelium-denuded arteries. Moreover, endothelium-dependent responses to BHT-920 and isoproterenol were modified by L-NOARG. Tetraethylammonium (TEA) or 4-aminopyridine, the Ca2+-activated (K(Ca)) or voltage-dependent K+ (K(V)) channel blockers, respectively, enhanced the neurogenic contractions observed. TEA but not 4-aminopyridine increased NA-induced contractions. The ATP-sensitive K+ (K(ATP))-channel blocker glibenclamide failed to modify adrenergic contractions. Blockade of capsaicin-sensitive primary afferents increased EFS-induced contractions. In conclusion, adrenergic contractions are predominantly mediated by muscular alpha(1)-adrenoceptors, while endothelial alpha(2)- and beta-adrenoceptors play a minor role. Presynaptic alpha(2)- and beta-adrenoceptors cannot be precluded. Noradrenergic neurotransmission in rat radial artery seems to be modulated by both stimulation of endothelial NO, K(Ca), and K(V) channels and sensory C-fiber activation.

Comparative study of nicorandil and a spasmolytic cocktail in preventing radial artery spasm during transradial coronary angiography

BACKGROUND

Radial artery spasm is one of the most common complications during coronary angiography via the transradial approach, causing patient discomfort or sometimes interrupting the procedure. This study was designed to compare the spasmolytic effect between nicorandil and a cocktail during transradial coronary angiography.

METHODS

A randomized study to compare 4 mg of nicorandil and a cocktail (mixture of normal saline, 200 microg of verapamil) was performed in 150 patients. We examined vasospasms of the radial artery that were expressed as stenosis of the radial artery vessel diameter after the procedure.

RESULT

The reductions of systolic and diastolic blood pressures showed no significant differences between the two groups (15.4+/-11.5/7.7+/-7.8 mmHg for nicorandil and 16.3+/-13.4/6.2 mmHg for cocktail). Both agents induced a significant radial artery vasodilation after transradial administration at proximal and mid segments (P < 0.001 for all). Nicorandil showed a significant increase of the mean change of the radial artery diameter compared to the cocktail at mid-segment (0.32+/-0.23 mm for nicorandil and 0.24+/-0.15 mm for a cocktail, P < 0.05). There was no statistically significant difference between the two groups in radial artery spasm (50.7% vs. 52.0% in nicorandil and a cocktail, respectively) after catheterization.

CONCLUSION

Nicorandil with vasodilator effects by a dual mechanism was effective as the cocktail in preventing radial artery spasm during transradial coronary angiography.

Potassium channel opener pinacidil induces relaxation of the isolated human radial artery

Taking into consideration that the search for drugs capable of modifying blood flow through human radial artery (RA) is warranted, the present study was designed to examine the vasodilatatory effects of the potassium channel opener, pinacidil on the RA and to define the contribution of different K+ -channel subtypes in the endothelium-independent pinacidil action on this blood vessel. Pinacidil relaxed the RA rings with endothelium and without endothelium with comparable potency. N-nitro-L-arginine methyl ester (L-NAME) and methylene blue did not affect the pinacidil-induced vasorelaxation in rings with endothelium. In the rings without endothelium, the K+ -channel blockers glibenclamide and tetraethylammonium (TEA) moderately antagonized the pinacidil-induced relaxation, while charybdotoxin and 4-aminopiridine did not. In endothelium-denuded rings, precontracted with 100 mM K+, the relaxant responses to pinacidil were highly significantly shifted to the right compared to those obtained in RA precontracted with phenylephrine, but pinacidil-induced maximal relaxation was not affected. Addition of nifedipine did not but addition of nifedipine and nickel (Na+ -Ca2+ exchanger inhibitor) did cause a statistically significant rightward shift of the pinacidil concentration-relaxation curve, although the effect 0.1 mM pinacidil was preserved. Thus, pinacidil induces relaxation of the human RA in endothelium-independent manner, and glibenclamide- and TEA-sensitive vascular smooth muscle K+ channels are probably involved. Its ability to completely relax the RA precontracted with K+ -rich solution suggests that pinacidil has additional K+ channel-independent mechanism(s) of action. It seems that stimulation of the forward mode of the Na+ -Ca2+ exchanger plays a part in this K+ channel-independent effect of pinacidil.

Testosterone Relaxes Isolated Human Radial Artery by Potassium Channel Opening Action

Preliminary clinical studies of testosterone therapy in male patients with coronary artery disease obtained promising results. However, little is known about the in vitro effects of testosterone in human isolated arteries. We investigated the effect of testosterone on contractile tone of human isolated radial artery (RA). Testosterone was added (0.1 - 300 microM ) cumulatively to organ baths after precontraction with KCl (45 mM) and phenylephrine (PE, 10 microM). Testosterone-induced relaxations were tested in the presence of the cyclooxygenase inhibitor indomethacin (10 microM), nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM), non-selective large conductance Ca(2+)-activated and voltage-sensitive K(+) channel inhibitor tetraethylammonium (TEA, 1 mM), ATP-sensitive K(+) channel inhibitor glibenclamide (GLI, 10 microM), and voltage-sensitive K(+) channel inhibitor 4-aminopyridine (4-AP, 1 mM). Testosterone produced relaxation in human RA (E(max): 53.03 +/- 2.76% and 66.83 +/- 1.97% of KCl and PE-induced contraction, respectively). Except for GLI, the relaxation to testosterone is affected by neither K(+) channel inhibitors (TEA, BaCl(2), and 4-AP), L-NAME, nor indomethacin. We report for the first time that supraphysiological concentrations of testosterone induces relaxation in RA. This response may occur in part via ATP-sensitive K(+) channel opening action.

Analysis of Vasoreactivity of Isolated Human Radial Artery

Radial artery (RA) is increasingly used as graft for coronary artery bypass grafting due to its good long-term patency. However, the mechanism of peri- and post-operative spasm is still unclear. Because of that, the aim of our study is to analyze the contractility of RA and to determine whether the presence of functional endothelium alters its contractile properties. Contractions of isolated RA rings were provoked by exogenously applied vasoconstrictors or by electrical field stimulation (EFS, 20 Hz). The order of vasoconstrictors potency based on their EC50 values was as follows: angiotensin II > phenylephrine > 5-hydroxytriptamine. Presence of endothelium increased both EC50 and maximal contraction to phenylephrine and angiotensin II, but inhibited reactivity of RA to 5-hydroxytriptamine. Spontaneous rhythmic contractions (SRC, <4 mHz) and EFS-induced contractions of RA are endothelium-independent and weaker than contractions induced by exogenously applied vasoconstrictors. Our study concludes that RA shows marked sensitivity and reactivity to angiotensin II, phenylephrine, and 5-hydroxytriptamine. Further investigations are necessary to answer why angiotensin II and phenylepehrine induce stronger contractions in the presence of endothelium. In addition, SRC as well as contractions of neurogenic origin may take part in developing vascular spasm of RA.

Comparative Effects of Tolazoline and Nitroprusside on Human Isolated Radial Artery

BACKGROUND

The radial artery is increasingly being used in coronary revascularization as an alternative conduit to a saphenous vein graft. Its perfect endothelial capacity provides a high patency rate comparable with the internal mammary artery (IMA). However, its spastic characteristics cause difficulties during its intraoperative preparation and may lead to early postoperative graft failure. Thus, treatment and/or prevention of radial artery spasm with an effective vasodilator agent is essential for its longevity. Endogenous vasoconstrictors, including noradrenaline, endothelin-1, and thromboxane A2, are likely to play a role in the pathogenesis of graft spasm. In the present study, we evaluated the vasorelaxant effect of tolazoline, a nonselective alpha-adrenoceptor blocker, against the contractions induced by various spasmogenic agents in an isolated human radial artery.

METHODS

Tolazoline (10(-9)-10(-4) M) or sodium nitroprusside (SNP, 10(-9)-10(-4) M) were cumulatively applied on radial artery rings precontracted submaximally with noradrenaline, endothelin-1, thromboxane analogue, U46619, or potassium chloride. In addition, some rings were pretreated with tolazoline (4 x 10(-6) M) for 30 minutes and the contractile response curve to noradrenaline was assessed in its presence.

RESULTS

Tolazoline effectively reversed noradrenaline-induced contractions in the radial artery, whereas it failed to produce remarkable relaxations on rings contracted with other spasmogenic agents, while SNP overcame the contractions induced by all spasmogens to a similar extent. In addition, brief pretreatment of radial artery rings with tolazoline significantly inhibited the contractions to noradrenaline.

CONCLUSIONS

Tolazoline is not as broadly effective as SNP against all spasmogens investigated; however, it may be effective in counteracting alpha-adrenoceptor-mediated vasospasm in human radial arteries.

Radial Artery Graft for Coronary Artery Bypass Surgery: Biological Characteristics and Clinical Outcome

The radial artery (RA) is gaining popularity as a bypass conduit for coronary artery bypass grafting, and its impact on clinical practice has been extensively explored. In the present article, we provide a review of postoperative hand circulation, vascular biological characteristics of the RA graft, the efficacy of vasodilator therapies, and mid-term clinical results of use of the RA graft. Fundamental studies revealed excellent vascular biological characteristics of the RA graft as a living arterial conduit, making it almost equivalent to the internal thoracic artery (ITA) graft. Clinical studies have yielded encouraging mid-term results. Most studies reported in favor of the RA graft over the saphenous vein graft with regard to patency rate, freedom from cardiac events, and survival. However, superiority of either the RA or right ITA graft has not been conclusively determined. The long-term results of RA grafts remain unknown, but at present, supplementary use of an RA graft with a left ITA graft appears feasible for CABG.

The calcium channel blocker amlodipine exerts its anti¬proliferative action via p21 (Waf1/Cip1) gene activation

Proliferation of vascular smooth muscle cells (VSMC) contributes to the progression of atherosclerotic plaques. Calcium channel blockers have been shown to reduce VSMC proliferation, but the underlying molecular mechanism remains unclear. p21(Waf1/Cip1) is a potent inhibitor of cell cycle progression. Here, we demonstrate that amlodipine (10(-6) to 10(-8) M) activates de novo synthesis of p21(Waf1/Cip1) in vitro. We show that amlodipine-dependent activation of p21(Waf1/Cip1) involves the action of the glucocorticoid receptor (GR) and C/EBP-alpha. The underlying pathway apparently involves the action of mitogen-activated protein kinase or protein kinase C, but not of extracellular signal-related kinase or changes of intracellular calcium. Amlodipine-induced p21(Waf1/Cip1) promoter activity and expression were abrogated by C/EBP-alpha antisense oligonucleotide or by the GR antagonist RU486. Amlodipine-dependent inhibition of cell proliferation was partially reversed by RU486 at 10(-8) M (58%+/-29%), antisense oligonucleotides targeting C/EBP-alpha (91%+/-26%), or antisense mRNAs targeting p21(Waf1/Cip1) (96%+/-32%, n=6); scrambled antisense oligonucleotides or those directed against C/EBP-beta were ineffective. The data suggest that the anti-proliferative action of amlodipine is achieved by induction of the p21 (Waf1/Cip1) gene, which may explain beneficial covert effects of this widely used cardiovascular therapeutic drug beyond a more limited role as a vascular relaxant.

In vitro effects of antihypertensive drugs on thromboxane agonist (U46619)-induced vasoconstriction in human internal mammary artery

BACKGROUND

Hypertension is a major problem in the perioperative period of cardiac and non-cardiac surgery. The vascular endothelium plays a crucial role in modulating vascular tone by producing vasodilators as well as vasoconstrictors. Thromboxane A2 (TxA2), a prototypical vasoconstrictor produced by endothelium and platelets, may play an important role in the pathogenesis of hypertension and subsequent ischaemic events. Although multiple drugs are currently available to treat perioperative hypertension, there is a paucity of data comparing these agents. Therefore, we examined the in vitro vascular effects of commonly used antihypertensive drugs on human internal mammary artery (IMA) segments.

METHODS

Relaxation responses to adenosine (a nucleoside), enalaprilat (a competitive inhibitor of angiotensin-converting enzyme), fenoldopam (a D1-dopamine receptor agonist), hydralazine, labetalol (an alpha- and beta-adrenergic blocker), nicardipine (a calcium channel blocker), nicorandil (K(+)-ATP channel opener), nitroglycerin (GTN, a nitrosovasodilator), and sodium nitroprusside (SNP, a nitrosovasodilator) were studied in IMA segments pre-contracted with the TxA2 analogue (U46619, 1.0 x 10(-8) M). Effects of labetalol were also studied in IMA segments pre-contracted with norepinephrine (1.0 x 10(-6) M). All drugs were added in a cumulative fashion (range 10(-10) to 10(-3) M).

RESULTS

All agents in the current study, with the exception of enalaprilat, dilated the IMA segments pre-contracted with U46619. Only GTN and SNP induced a complete (90-100%) relaxation. The order of efficacy of the in vitro relaxation was as follows: SNP, GTN, nicardipine, nicorandil, fenoldopam, hydralazine, adenosine, and labetalol. The potency was in the order of GTN, SNP, fenoldopam, nicorandil, hydralazine, adenosine, and nicardipine.

CONCLUSIONS

Various antihypertensive agents are effective in attenuating U46619-induced IMA vasoconstriction, but the efficacy and potency differ. The in vitro vasodilation may not be simply extrapolated to the clinical efficacy or outcome of each antihypertensive therapy; however, our data provide additional grounds for the choice of antihypertensive medication. Further clinical studies are needed to help to fully elucidate the use of different antihypertensive agents and clinical outcomes.

Radial artery as conduit for distal renal artery reconstruction

Reconstruction of the renal artery with both saphenous vein and prosthetic material as bypass graft is durable in atherosclerotic disease. Extensive experience with saphenous vein grafts in pediatric patients and patients without atherosclerosis reveals a disturbing incidence of vein graft aneurysm degeneration. Distal renal artery reconstruction involving small branch vessels is generally not amenable to prosthetic reconstruction. We report a new approach to distal renal artery bypass grafting to avert these limitations.

CASE

A 43-year-old man with previously normal blood pressure had malignant hypertension, which proved difficult to control despite use of a beta-blocker and an angiotensin II inhibitor. At renal angiography a fusiform aneurysm was revealed in a posterior branch of the right renal artery. The renal artery aneurysm was resected, and the left radial artery was harvested and used as a sequential aortorenal bypass graft to the two branch renal arteries. The postoperative course was uneventful, and the patient now has normal blood pressure with a calcium channel blocker for maintenance of the radial artery graft. Pathologic analysis revealed a pseudoaneurysm with dissection between the media and external lamella, consistent with fibromuscular dysplasia.

CONCLUSION

Autologous artery is the preferred conduit for renal reconstruction in the pediatric population. On the basis of cardiac surgery experience, we used the radial artery and found it to be a technically satisfactory conduit for distal renal reconstruction in a patient without atherosclerosis.