Alpha-adrenoceptor blockade prevents exercise-induced vasoconstriction of stenotic coronary arteries

Comparative Investigation of Protective Effects of Metyrosine and Metoprolol Against Ketamine Cardiotoxicity in Rats

This study investigated the effect of metyrosine against ketamine-induced cardiotoxicity in rats and compared the results with the effect of metoprolol. In this study, rats were divided into groups A, B and C. In group A, we investigated the effects of a single dose of metyrosine (150 mg/kg) and metoprolol (20 mg/kg) on single dose ketamine (60 mg/kg)-induced cardiotoxicity. In group B, we investigated the effect of metyrosine and metoprolol, which were given together with ketamine for 30 days. In group C, we investigated the effect of metyrosine and metoprolol given 15 days before ketamine and 30 days together with ketamine on ketamine cardiotoxicity. By the end of this process, we evaluated the effects of the levels of oxidant-antioxidant parameters such as MDA, MPO, 8-OHGua, tGSH, and SOD in addition to CK-MB and TP I on cardiotoxicity in rat heart tissue. The experimental results show that metyrosine prevented ketamine cardiotoxicity in groups A, B and C and metoprolol prevented it in only group C.

Antagonism of Nav channels and α1-adrenergic receptors contributes to vascular smooth muscle effects of ranolazine

Ranolazine is a recently developed drug used for the treatment of patients with chronic stable angina. It is a selective inhibitor of the persistent cardiac Na⁺ current (I_Na), and is known to reduce the Na⁺-dependent Ca²⁺ overload that occurs in cardiomyocytes during ischemia. Vascular effects of ranolazine, such as vasorelaxation,have been reported and may involve multiple pathways. As voltage-gated Na⁺ channels (Na_v) present in arteries play a role in contraction, we hypothesized that ranolazine could target these channels. We studied the effects of ranolazine in vitro on cultured aortic smooth muscle cells (SMC) and ex vivo on rat aortas in conditions known to specifically activate or promote I_Na. We observed that in the presence of the Na_v channel agonist veratridine, ranolazine inhibited I_Na and intracellular Ca²⁺ calcium increase in SMC, and arterial vasoconstriction. In arterial SMC, ranolazine inhibited the activity of tetrodotoxin-sensitive voltage-gated Na_v channels and thus antagonized contraction promoted by low KCl depolarization. Furthermore, the vasorelaxant effects of ranolazine, also observed in human arteries and independent of the endothelium, involved antagonization of the α₁-adrenergic receptor. Combined α₁-adrenergic antagonization and inhibition of SMCs Na_v channels could be involved in the vascular effects of ranolazine.

Reprint of: the paradox of α-adrenergic coronary vasoconstriction revisited

Activation of coronary vascular α-adrenoceptors results in vasoconstriction which competes with metabolic vasodilation during sympathetic activation. Epicardial conduit vessel constriction is largely mediated by α(1)-adrenoceptors; the constriction of the resistive microcirculation largely by α(2)-adrenoceptors, but also by α(1)-adrenoceptors. There is no firm evidence that α-adrenergic coronary vasoconstriction exerts a beneficial effect on transmural blood flow distribution. In fact, α-blockade in anesthetized and conscious dogs improves blood flow to all transmural layers, during normoperfusion and hypoperfusion. Also, in patients with coronary artery disease, blockade of α(1)- and α(2)-adrenoceptors improves coronary blood flow, myocardial function and metabolism. This article is part of a Special Issue entitled "Coronary Blood Flow".

Efficacy of longitudinal speckle tracking strain in conjunction with isometric handgrip stress test for detection of ischemic myocardial segments

BACKGROUND

Isometric handgrip stress test is a simple method for detecting coronary artery disease (CAD). However, the value of this method alone is limited by relatively low sensitivity. This study thus aimed to investigate the usefulness of two-dimensional speckle-tracking strain combined with handgrip for CAD patients.

METHOD

We studied 35 patients with stable angina pectoris who underwent percutaneous coronary intervention (PCI). Longitudinal (L-ɛ) and transverse peak systolic (T-ɛ) strains were measured from three standard apical views before and 1 month after PCI. Segments corresponded to perfusion territories of coronary arteries were divided into two groups based on coronary angiography results: stenotic (S) and nonstenotic (NS) segment.

RESULTS

L-ɛ in S segments increased significantly after PCI, from -15.8% to -17.6% (P < 0.01), but not in NS segments. Moreover, L-ɛ in S segments increased significantly during handgrip before PCI, from -15.8% to -17.6% (P < 0.01), but decreased after PCI, from -17.6% to -16.7% (P = 0.02). In contrast, L-ɛ in NS segments decreased significantly during the isometric handgrip stress test before and after PCI (P < 0.05). Especially noteworthy is that a relative change in L-ɛ of >1.2% during handgrip before PCI could detect significant coronary stenosis with a sensitivity of 80%, specificity of 66%, and area under the curve of 0.77 (P < 0.001). On the other hand, no significant changes were observed in either T-ɛ segments during handgrip either before or after PCI.

CONCLUSION

Longitudinal speckle-tracking strain combined with handgrip may constitute a valuable tool for detection of ischemic myocardial segments and prediction of improvement of regional contraction after revascularization.

Effects of verbal suggestion on coronary arteries: results of a randomized controlled experimental investigation during coronary angiography

BACKGROUND

Decrease of chest pain perception under placebo conditions has been frequently observed. The aim of this study was to examine whether placebo-induced chest pain improvement could be the result of changes in coronary blood flow. We, therefore, performed an experiment to investigate whether a verbal suggestion (VS) integrated in a cardiologic procedure has an impact on diameters of coronary arteries.

METHODS

A total of 30 chest pain patients with normal diagnostic angiograms were assigned to a VS or a control group (CG). Saline solution was administered intracoronarily to both groups. The VS group received a standardized VS, implying coronary vasodilation. The CG remained without VS. Coronary end points were the changes in percentage diameter stenosis, Minimal lumen diameter and reference diameter of the index coronary segment before and 60 seconds after the administration of saline. Furthermore, changes in hemodynamics, psychological distress, and chest pain perception were recorded.

RESULTS

The VS led to coronary vasoconstriction in comparison with CG (change in mean percentage diameter stenosis ± SD 3.2% ± 6.3% vs -1.7% ± 6.8%, P = .062; change in mean minimal lumen diameter ± SD -0.18 ± 0.32 mm vs 0.06 ± 0.23 mm, P = .029, no relevant change in the reference diameter). At the same time, the degree of chest pain perception was significantly reduced in the VS group (-0.7 ± 1.3) compared with the CG (0.3 ± 1.3), P = .024.

CONCLUSION

The findings of this study suggest that a VS results in a biological alteration within coronary arteries. Contrary to expectation, the VS led to vasoconstriction, whereas chest pain perception decreased.

Coronary microvascular resistance: methods for its quantification in humans

Coronary microvascular dysfunction is a topic that has recently gained considerable interest in the medical community owing to the growing awareness that microvascular dysfunction occurs in a number of myocardial disease states and has important prognostic implications. With this growing awareness, comes the desire to accurately assess the functional capacity of the coronary microcirculation for diagnostic purposes as well as to monitor the effects of therapeutic interventions that are targeted at reversing the extent of coronary microvascular dysfunction. Measurements of coronary microvascular resistance play a pivotal role in achieving that goal and several invasive and noninvasive methods have been developed for its quantification. This review is intended to provide an update pertaining to the methodology of these different imaging techniques, including the discussion of their strengths and weaknesses.

Dark Chocolate Improves Coronary Vasomotion and Reduces Platelet Reactivity

Background— Dark chocolate has potent antioxidant properties. Coronary atherosclerosis is promoted by impaired endothelial function and increased platelet activation. Traditional risk factors, high oxidative stress, and reduced antioxidant defenses play a crucial role in the pathogenesis of atherosclerosis, particularly in transplanted hearts. Thus, flavonoid-rich dark chocolate holds the potential to have a beneficial impact on graft atherosclerosis.

Methods and Results— We assessed the effect of flavonoid-rich dark chocolate compared with cocoa-free control chocolate on coronary vascular and platelet function in 22 heart transplant recipients in a double-blind, randomized study. Coronary vasomotion was assessed with quantitative coronary angiography and cold pressor testing before and 2 hours after ingestion of 40 g of dark (70% cocoa) chocolate or control chocolate, respectively. Two hours after ingestion of flavonoid-rich dark chocolate, coronary artery diameter was increased significantly (from 2.36±0.51 to 2.51±0.59 mm, P <0.01), whereas it remained unchanged after control chocolate. Endothelium-dependent coronary vasomotion improved significantly after dark chocolate (4.5±11.4% versus −4.3±11.7% in the placebo group, P =0.01). Platelet adhesion decreased from 4.9±1.1% to 3.8±0.8% ( P =0.04) in the dark chocolate group but remained unchanged in the control group.

Conclusions— Dark chocolate induces coronary vasodilation, improves coronary vascular function, and decreases platelet adhesion 2 hours after consumption. These immediate beneficial effects were paralleled by a significant reduction of serum oxidative stress and were positively correlated with changes in serum epicatechin concentration.

Handgrip-enhanced myocardial fractional flow reserve for assessment of coronary artery stenoses

BACKGROUND

Fractional flow reserve (FFR) may yield false-negative results in up to 12% of lesions tested, and there is a zone of uncertainty at borderline values.

METHODS

Forty-eight patients were investigated by means of dobutamine stress echocardiography (DSE), coronary angiography, and FFR assessment of 48 coronary lesions before, during, and immediately after handgrip exercise.

RESULTS

Mean FFR values were lower during and immediately after handgrip exercise as compared with baseline (0.86 +/- 0.09 vs 0.87 +/- 0.08 vs 0.88 +/- 0.08, P < .05, respectively). The sensitivity of FFR < or = 0.75 for predicting myocardial ischemia on DSE was 17.6% before handgrip exercise, 52.9% during, and 35.5% immediately after exercise. The specificity of FFR < or = 0.75 before, during, and immediate after exercise was 100%, 93.5%, and 96.8%, respectively. In 10 patients, FFR values > 0.75 before handgrip became < or = 0.75 during or immediately after handgrip exercise (P = .01). All these patients had angina and/or DSE indicating ischemia in the territory of the vessel studied, and underwent coronary intervention. At 6 months follow-up, all patients were asymptomatic with negative DSE tests.

CONCLUSIONS

The addition of handgrip exercise can significantly lower the FFR and potentially improve its ability to detect physiologically significant stenoses.

Effect of phentolamine on the hyperemic response to adenosine in patients with microvascular disease

For accurate measurement of the fractional flow reserve (FFR) of the myocardium, the presence of maximum hyperemia is of paramount importance. It has been suggested that the hyperemic effect of the conventionally used hyperemic stimulus, adenosine, could be submaximal in patients who have microvascular dysfunction and that adding alpha-blocking agents could augment the hyperemic response in these patients. We studied the effect of the nonselective alpha-blocking agent phentolamine, which was administered in addition to adenosine after achieving hyperemia, in patients who had microvascular disease and those who did not. Thirty patients who were referred for percutaneous coronary intervention were selected. Of these 30 patients, 15 had strong indications for microvascular disease and 15 did not. FFR was measured using intracoronary adenosine, intravenous adenosine, and intracoronary papaverine before and after intracoronary administration of the nonselective alpha blocker phentolamine. In patients who did not have microvascular disease, no differences in hyperemic response to adenosine were noted, whether or not alpha blockade was given before adenosine administration; FFR levels before and after phentolamine were 0.76 and 0.75, respectively, using intracoronary adenosine (p = 0.10) and 0.75 and 0.74, respectively, using intravenous adenosine (p = 0.20). In contrast, in patients who had microvascular disease, some increase in hyperemic response was observed after administration of phentolamine; FFR levels decreased from 0.74 to 0.70 using intracoronary adenosine (p = 0.003) and from 0.75 to 0.72 using intravenous adenosine (p = 0.04). Although statistically significant, the observed further decrease in microvascular resistance after addition of phentolamine was small and did not affect clinical decision making in any patient. In conclusion, when measuring FFR, routinely adding an alpha-blocking agent to adenosine does not affect clinical decision making.

Coronary Artery Vasospasm During Dobutamine Stress Echocardiography

Compared with the frequent occurrence of S-T segment depression, the development of S-T segment elevation during dobutamine stress echocardiography is a relatively rare finding, especially in the setting of nonobstructive coronary artery disease. We present two patients who developed chest discomfort with S-T segment elevation during dobutamine stress testing. Both patients had unremarkable baseline echocardiograms and no history suggestive of coronary vasospasm. Subsequent coronary angiography revealed nonobstructive disease. It is speculated that the likely presence of endothelial dysfunction coupled with mild coronary atherosclerosis caused an imbalance between the coronary vasodilatory and vasoconstrictive forces. The inhibition of the vasodilatory effects of beta-adrenergic receptor stimulation and flow-mediated dilation of dobutamine was overcome by the vasoconstrictive effects of dobutamine-stimulated alpha-1 receptor activation; thus, contributing to the development of coronary vasospasm. This condition is important to recognize and appreciate as the initial treatment for this condition favors the use of nitrates over beta-blockade.

Role of β 2 Adrenergic Receptors in Human Atherosclerotic Coronary Arteries

Background— Adrenergic regulation of coronary vasomotion is balanced between α 1 -adrenergic–mediated (α 1 -AR) constriction and β 2 -adrenergic–mediated (β 2 -AR) relaxation. This study aimed at assessing the role of β 2 -ARs in normal, mildly atherosclerotic, and stenotic human coronary arteries.

Methods and Results— During intracoronary (IC) infusion of increasing doses of the β 2 -AR agonist salbutamol (0.15, 0.3, and 0.6 μg/min) and the endothelial vasodilator acetylcholine (1, 3, and 10 μg/min), we measured (1) changes in lumen diameter (LD) by quantitative coronary angiography in 34 normal, 55 mildly atherosclerotic, and 42 stenotic coronary artery segments and (2) changes in average peak velocity (APV) and coronary blood flow (CBF) with the use of Doppler flow wire in 11 normal, 10 mildly atherosclerotic, and 11 stenotic coronary arteries. In 6 of 11 stenotic coronary arteries, the protocol was repeated after an IC bolus (12 μg/kg) of the α-adrenergic blocker phentolamine. In 6 of 11 normal coronary arteries, the protocol was repeated after an IC infusion (60 μmol/min) of N G -monomethyl- l -arginine (L-NMMA), a nitric oxide inhibitor. Neither salbutamol IC infusion nor acetylcholine significantly changed heart rate or blood pressure, whereas L-NMMA slightly increased blood pressure. In normal coronary arteries, salbutamol increased LD (LD max %: 11±2, P <0.05), APV (APV max %: 53±17, P <0.05), and CBF (CBF max %: 57±17, P <0.05), whereas L-NMMA caused a blunted APV (APV max %: 27±6, P <0.05) and CBF (CBF max %: 29±6, P <0.05) response to salbutamol. In mildly atherosclerotic coronary arteries, the salbutamol increase in LD (LD max %: 10±2, P <0.05), APV (APV max %: 33±12, P <0.05), and CBF (CBF max %: 37±12, P <0.05) was preserved. In stenotic coronary arteries, salbutamol induced a paradoxical reduction in LD (LD max %: −6±2, P <0.05), APV (APV max %: −15±9, P <0.05), and CBF (CBF max %: −15±6, P <0.05), which was no longer observed after phentolamine. Acetylcholine increased LD (LD max %: 14±3, P <0.05), APV (APV max %: 61±20, P <0.05), and CBF (CBF max %: 67±19, P <0.05) in normal coronary arteries. In mildly atherosclerotic coronary arteries, acetylcholine induced a significant reduction in LD (LD max %: −15±2, P <0.05) and no changes in APV (APV max %: −6±13, P =NS) and CBF (CBF max %: −10±13, P =NS). In stenotic coronary arteries, acetylcholine significantly reduced LD (LD max %: −15±3, P <0.05), APV (APV max %: −15±9, P <0.05), and CBF (CBF max %: −15±6, P <0.05).

Conclusions— In severely atherosclerotic coronary arteries, β 2 -adrenergic vasodilatation is impaired, and this might contribute to alter the vasomotor balance, further precipitating myocardial ischemia during sympathetic activation.

Effects of intravenous dobutamine on coronary vasomotion in humans

OBJECTIVES

We sought to investigate the vascular mechanisms of dobutamine-induced myocardial ischemia.

BACKGROUND

Dobutamine stress is often used as a surrogate for exercise. The effects of dobutamine on the epicardial arteries are incompletely understood and possibly different from those of physical exercise.

METHODS

Intravenous (IV) dobutamine (40 microg/kg per min) was administered in 19 patients with normal, 23 patients with mildly atherosclerotic, and 12 patients with stenotic coronary arteries. In another two groups of patients with stenotic arteries, IV dobutamine was preceded by 1) an intracoronary (IC) bolus of the alpha-adrenergic blocker phentolamine (12 microg/kg, n = 12); and 2) an IC infusion of the nitric oxide substrate L-arginine (150 micromol/l per min for 20 min, n = 11). Intravenous saline instead of dobutamine was infused into eight patients with normal arteries. After dobutamine (or saline), an IC bolus of isosorbide dinitrate (ISDN, 0.2 mg) was given. Coronary vasomotion was evaluated by quantitative coronary angiography on angiograms obtained after each dose of dobutamine, saline, phentolamine, L-arginine, and ISDN.

RESULTS

Dobutamine increased the rate-pressure product and heart rate similarly in all patients except those who received saline. Dobutamine induced vasodilation in normal (change in luminal diameter [DeltaLD] vs. baseline: 19 +/- 2%) and in mildly atherosclerotic arteries (DeltaLD: 8 +/- 2%, p < 0.05 vs. normal). In stenotic arteries, dobutamine did not induce significant vasomotion (DeltaLD: -3 +/- 3%); the latter was improved by L-arginine (DeltaLD: 10 +/- 3%, p < 0.05 vs. stenotic arteries) and fully restored by phentolamine (DeltaLD: 19 +/- 3%, p < 0.05 vs. stenotic arteries).

CONCLUSIONS

Endothelial dysfunction and enhanced alpha-adrenergic tone contribute to the loss of dobutamine-induced vasodilation in coronary atherosclerosis. In contrast to physical exercise, dobutamine does not induce "paradoxical vasoconstriction" of atherosclerotic coronary arteries.

[Analysis of differences in flow-mediated dilation in relation to the treatment of coronary patients]

INTRODUCTION

Flow-mediated dilation (FMD) is thought to be related to the development of coronary disease. We were interested in knowing the degree of FMD in a large sample of coronary patients in relation to the therapy they were given in clinical practice.

PATIENTS AND METHOD

We studied 1,081 coronary patients (age 68 +/- 12 years, 73% male) in which FMD was evaluated in the brachial artery. The patients were classified into 5 treatment groups (416 who receive 2 or more treatments were excluded): group A: 81 controls treated with aspirin, group B: 198 treated with ACE inhibitors, group C: 106 with calcium antagonists, group D: 145 with beta-blockers, and group E: 135 with lipid lowering medication (93% statins).

RESULTS

ANOVA was used to analyze the differences between groups. With regard to the number of risk factors present in each group, the patients treated with ACE inhibitors (2.44 +/- 0.79 vs 2.14 +/- 0.89; p < 0.05) and statins (3.45 +/- 0.70 vs 2.14 +/- 0.89; p < 0.05) had more risk factors than GrA and higher levels of LDL-cholesterol (ACE inhibitors 145.0 +/- 33.5 vs 128.5 +/- 32.2 and statins 157.8 +/- 45.3 vs 128.5 +/- 32.2; p < 0.05). GrB had a higher glycemia than controls (123.4 +/- 32.2 vs 114.7 +/- 33.7; p < 0.05). The control group was younger than the therapeutic groups (p < 0.05). Compared with the control group, FMD was significantly higher only in the group treated with ACE inhibitors (3.42 +/- 6.01 vs 0.82 +/- 6.04; p < 0.05). Multivariate logistical regression showed that treatment with ACE inhibitors and statins (p < 0.05) were independent predictors of FMD > 4%.

CONCLUSION

Treatment with ACE inhibitors or statins was predictive of the normalization of FMD in coronary patients in clinical practice.

Effect of vasodilatory beta-adrenoceptor blockers on cardiovascular haemodynamics in anaesthetized rats

1. The effect of vasodilatory beta-adrenoceptor blockers on regional blood flow in the major organs of anaesthetized rats was investigated using radioactive microspheres. The administration of propranolol and saline was used as a control. 2. Intravenous injections of carvedilol (2 mg/rat), celiprolol (20 mg/rat) and bopindolol (1 mg/rat) equally decreased systemic blood pressure (SBP) by approximately 20 mmHg, whereas propranolol (1 mg/rat) decreased SBP only slightly but not significantly. 3. Heart rate was significantly decreased by carvedilol, celiprolol, bopindolol and propranolol. 4. Coronary blood flow was markedly increased by carvedilol, but not by the other three drugs. 5. Cardiac output tended to decrease following the administration of all four drugs. 6. Total peripheral vascular resistance was not significantly affected by carvedilol, celiprolol and bopindolol, but was markedly increased following propranolol. 7. Renal blood flow was markedly increased by carvedilol. 8. Blood flow in the brown fat was markedly increased by carvedilol and bopindolol, but not by celiprolol and propranolol. 9. These findings indicate that the newer vasodilatory beta-blockers, such as carvedilol and bopindolol, have a beneficial effect on the regional circulation in contrast with the classical beta-blocker propranolol. 10. The regional haemodynamic effects observed in the present study following intravenous injection of the beta-blockers may help explain the clinical experience that vasodilatory beta-blockers increase insulin sensitivity and decrease mortality in patients with congestive heart failure.

Paradoxical Increase in Microvascular Resistance During Tachycardia Downstream From a Severe Stenosis in Patients With Coronary Artery Disease

Background —The pathophysiology of microvascular response to a severe coronary stenosis has not been conclusively identified. The aim of this study was to characterize the human vasomotor response to pacing-induced ischemia of both the stenotic arterial segment and the distal microcirculation.

Methods and Results —Sixteen patients with stable angina and single-vessel disease were studied. Blood flow velocity and transstenotic pressure gradient were monitored at baseline, after intracoronary adenosine (2 mg), and during ischemia induced by atrial pacing with and without adenosine. At the end of this protocol, the study was repeated after intracoronary phentolamine in 7 patients and after angioplasty in 9. Stenosis resistance was calculated as the ratio between mean pressure gradient and mean flow, and microvascular resistance as the ratio between mean distal pressure and mean flow; values were expressed as percent of baseline. Adenosine decreased ( P <0.05) baseline microvascular resistance to 52±17%, but not stenosis resistance. Pacing increased both stenosis and microvascular resistances (244±96% and 164±60% of baseline, respectively, P <0.05). Addition of adenosine to pacing decreased both stenosis (143±96% of baseline, P <0.05 versus ischemia) and microvascular (51±17% of baseline, P <0.05 versus baseline and ischemia) resistances. Phentolamine did not affect coronary resistance at any step of the protocol. Angioplasty and stenting restored a progressive decline in microvascular resistance during pacing (51±19% of baseline, P <0.05 versus baseline).

Conclusions —In patients with coronary artery disease, tachycardia-induced ischemia was associated with elevated resistance of both the stenotic segment and the microvasculature. Revascularization prevents this paradoxical behavior.

Distension of urinary bladder induces exaggerated coronary constriction in smokers with early atherosclerosis

Distension of the urinary bladder causes an increase in efferent sympathetic activity, which can precipitate myocardial ischemia. Smoking has been shown to modulate activities of afferent nerves from the distended urinary bladder and to impair endothelial function in response to sympathetic activation. To assess the effect of bladder distension on coronary dynamics in smokers, we measured epicardial and microvascular responses in 24 patients with early atherosclerosis (< 50% diameter stenosis). Patients were classified into habitual smokers (group 1, n = 14) and nonsmokers (group 2, n = 10). Habitual smokers were randomized into two subgroups on the basis of the use of doxazosin, as follows: subgroup 1A (n = 7), without administration of doxazosin before catheterization; subgroup 1B (n = 7), with dosing doxazosin. In response to bladder distension (mean intravesical pressure 21.5 mmHg), bladder distension significantly decreased coronary diameter at the stenotic segments, coronary blood flow, and increased coronary resistance compared with baseline values, in subgroup 1A patients. In subgroup 1B patients during bladder distension, coronary diameter, coronary blood flow, and coronary resistance did not show significant changes compared with baseline values. There were significant differences of coronary diameter at the stenotic segments, coronary blood flow, and of changes of coronary vascular resistance between subgroup 1A and group 2 during bladder distension, despite similar changes in rate-pressure product. The present study showed that urinary bladder distension caused an abnormal vasomotor response of epicardial vasoconstriction and a concomitant increased coronary resistance, which leads to reduction in coronary blood flow in patients with early atherosclerosis. Smoking may further impair the response, implying that smoking has exaggerated response to sympathetic stimulation of conduit and resistance vessels. The abnormal response was abolished by pretreated administration of doxazosin, suggesting that the involved mechanisms are related to alpha(1)-adrenoceptors.

Limitation of coronary reserve after successful angioplasty is prevented by oral pretreatment with an alpha1-adrenergic antagonist

Coronary vasoconstriction that occurs after percutaneous transluminal coronary angioplasty (PTCA) is abolished by intracoronary phentolamine. An impairment of coronary vasodilator reserve (CVR) has been observed < or = 7 days after successful PTCA. To ascertain whether pretreatment with the alpha1-adrenergic receptor blocker doxazosin could prevent the limitation of CVR after PTCA, we carried out a randomised, double-blind, controlled study on 26 patients with significant (> 75%) single vessel disease undergoing PTCA. Twelve patients received doxazosin 4 mg daily in addition to their standard treatment, while 14 patients received matching placebo, starting 11 days before PTCA. Myocardial blood flow (MBF) at baseline and after i.v. dipyridamole (0.56 mg/kg) was measured within 5 days after PTCA using positron emission tomography (PET) with oxygen-15-labelled water. Angioplasty was successful in all patients with a residual stenosis < or = 35%. At PET scanning, hemodynamic parameters were comparable in the two groups. In the territory subtended by the dilated artery, CVR was significantly higher in patients treated with doxazosin compared with those receiving placebo (2.78 +/- 0.1.21 vs. 1.95 +/- 0.68; p < 0.01). Conversely, CVR in the remote territories subtended by angiographically normal arteries was similar in the two groups (2.53 +/- 0.92 and 2.48 +/- 0.80, respectively; p = NS). Treatment with oral doxazosin in addition to standard antianginal therapy can prevent the impairment of CVR frequently observed despite successful PTCA.

Acute effects of urinary bladder distention on the coronary circulation in patients with early atherosclerosis

OBJECTIVES

We sought to examine whether distention of the urinary bladder, a physiologic stimulus, could induce impaired coronary circulation in patients with early atherosclerosis.

BACKGROUND

Distention of the urinary bladder reflexively causes an increase in sympathetic activity. The effect of such distention on the coronary circulation in patients with early atherosclerosis remains unknown.

METHODS

To assess the effect of bladder distention on coronary dynamic forces, epicardial and microvascular responses were measured with an intracoronary Doppler flow wire in 40 patients with early atherosclerosis (<50% diameter stenosis). Patients were randomized into two groups according to whether they did not (group 1, n = 20) or did have (group 2, n = 20) pretreatment with an alpha1-adrenergic receptor blocker (oral doxazosin, 2 mg). Coronary flow velocity was monitored by quantitative coronary angiography at baseline, during urinary bladder distention and after intracoronary nitroglycerin injection.

RESULTS

Bladder distention significantly decreased the coronary diameter in the stenotic segments (p<0.001), decreased coronary blood flow (p<0.001) and increased coronary resistance (p<0.001), as compared with baseline values, in group 1 patients. In group 2 patients with bladder distention, the angiographic variables did not show significant changes, as compared with baseline values. No significant differences were noted between the groups in the responses of the angiographic variables after nitroglycerin administration.

CONCLUSIONS

The present study shows, for the first time, that urinary bladder distention caused vasoconstriction of coronary conduit and resistance vessels involved mechanisms related to alpha1 adrenoceptors. Pretreated administration of doxazosin reversed the changes toward baseline. Vasoconstriction during bladder distention can be relieved after nitroglycerin administration, suggesting an unchanged responsiveness of vascular smooth muscle cells to such distention.

alpha-adrenergic coronary vasoconstriction and myocardial ischemia in humans

The use of quantitative coronary angiography, combined with Doppler and PET, has recently been directed at the study of alpha-adrenergic coronary vasomotion in humans. Confirming prior animal experiments, there is no evidence of alpha-adrenergic coronary constrictor tone at rest. Again confirming prior experiments, responses to alpha-adrenoceptor activation are augmented in the presence of coronary endothelial dysfunction and atherosclerosis, involving both alpha(1)- and alpha(2)-adrenoceptors in epicardial conduit arteries and microvessels. Such augmented alpha-adrenergic coronary constriction is observed during exercise and coronary interventions, and it is powerful enough to induce myocardial ischemia and limit myocardial function. Recent studies indicate a genetic determination of alpha(2)-adrenergic coronary constriction.