Responses Of Coronary Arteries Research Articles

Contractile responsiveness of coronary arteries from exercise-trained rats.

The purpose of this study was to determine whether exercise training alters vasomotor reactivity of rat coronary arteries. In vitro isometric microvessel techniques were used to evaluate vasomotor properties of proximal left anterior artery rings (1 ring per animal) from exercise-trained rats (ET; n = 10) subjected to a 12-wk treadmill training protocol (32 m/min, 15% incline, 1 h/day, 5 days/wk) and control rats (C; n = 6) restricted to cage activity. No differences in passive length-tension characteristics or internal diameter (158 +/- 9 and 166 +/- 9 micron) were observed between vessels of C and ET rats. Concentration-response curves to K+ (5-100 mM), prostaglandin F2alpha (10(-8)-10(-4) M), and norepinephrine (10(-8)-10(-4)) were unaltered (P > 0.05) in coronary rings from ET rats compared with C rats; however, lower values of the concentration producing 50% of the maximal contractile response in rings from ET rats (P = 0.05) suggest that contractile sensitivity to norepinephrine was enhanced. Vasorelaxation responses to sodium nitroprusside (10(-9)-10(-4) M) and adenosine (10(-9)-10(-4) M) were not different (P > 0.05) between vessels of C and ET rats. However, relaxation responses to the endothelium-dependent vasodilator acetylcholine (ACh; 10(-10)-10(-4) M) were significantly blunted (P < 0.001) in coronary rings from ET animals; maximal ACh relaxation averaged 90 +/- 5 and 46 +/- 12%, respectively, in vessels of C and ET groups. In additional experiments, two coronary rings (proximal and distal) were isolated from each C (n = 7) and ET (n = 7) animal. Proximal coronary artery rings from ET animals demonstrated decreased relaxation responses to ACh; however, ACh-mediated relaxation of distal coronary rings was not different between C and ET groups. NG-monomethyl-L-arginine (inhibitor of nitric oxide synthase) blocked ACh relaxation of all rings. L-Arginine (substrate for nitric oxide synthase) did not improve the blunted ACh relaxation in proximal coronary artery rings from ET rats. These studies suggest that exercise-training selectively decreases endothelium-dependent (ACh) but not endothelium-independent (sodium nitroprusside) relaxation responses of rat proximal coronary arteries; endothelium-dependent relaxation of distal coronary arteries is unaltered by training.

Reactivity-Based Coronary Vasospasm Independent of Atherosclerosis in Rhesus Monkeys

Objectives. We studied the hypothesis that in the absence of vascular pathology, coronary artery vasospasm occurs as a result of local regions of vascular muscle hyperreactivity. We aimed to explore the basis for a functional etiology of those vasospasms not explained on a structural basis.Background. Ovariectomized rhesus monkeys (Macaca mulatta) without injury or significant vascular disease were stimulated with platelet release products, and angiograms were compared with those from vasospasms induced in human patients.Methods. We used intracoronary (IC) injections of serotonin, thromboxane A2(U46619), endothelin 1 or angiotensin II in concentrations 3 to 10 times that which reduced coronary artery diameter by 50%.Results. Although no agent alone caused vasospasm, the combination of pathophysiologic concentrations of serotonin and the stable thromboxane A2mimetic, U46619, injected through an IC catheter, synergistically caused coronary vasospasm on the second or third challenge in five of seven monkeys. These drug-induced vasospasms were similar to vasospasms induced by mechanical injury followed by serotonin, and to those stimulated in human IC diagnostic tests, as judged by onset, appearance, kinetics and vasodilator reversal.Conclusions. These studies in ovariectomized monkeys revealed that coronary vasospasm can be stimulated without preexisting vascular pathology, endothelial denudation or injury. Reproducible vasospasm of primate coronary arteries in response to these two endogenous pathophysiologic vasoconstrictors, which are thought to be precipitating stimuli in the etiology of vasospasm, suggests that structure-independent epicardial vasospasm can be an important element in serious cardiac ischemic events, particularly the focal, persistent vasospasms that occur without plaques or injury.(J Am Coll Cardiol 1997;29:671–80)

Behavioral stress alters coronary vascular reactivity in borderline hypertensive rats.

Behavioral stress has been proposed to contribute to the occurrence of myocardial ischemia. Objective To investigate the effect of chronic exposure to behavioral stress on the function and structure of the coronary artery of borderline hypertensive rats (BHR). BHR were either exposed to an air-jet stress for 2 h/day for 10 days or kept in their cage for 10 days. After 10 days, hemodynamic measurements in conscious animals were recorded, and their hearts were removed for isolation of a left ventricular coronary artery for functional studies or for fixation by retrograde perfusion for study with scanning electron microscopy. Vascular reactivity was measured in isolated coronary arteries (approximately 250 microm) maintained at an intraluminal diameter of 40 mmHg while the intraluminal diameter was recorded continuously. The resting mean arterial pressure and heart rate in conscious, unrestrained BHR were not altered significantly by exposure to 10 days of 2 h/day air-jet stress. Coronary artery relaxation in response to the endothelium-dependent vasodilator acetylcholine was impaired in rats exposed to the air-jet stress compared with that in controls. An attenuated response to exogenous nitric oxide in coronary arteries from stressed BHR was confirmed by the finding of a reduced sensitivity to nitroprusside, which releases nitric oxide independently from the endothelium. However, relaxation of coronary arteries in response to isoproterenol, which acts independently from nitric oxide, was not altered. Coronary artery contraction in response to endothelin-1 and phenylephrine was not altered in vessels taken from BHR exposed to behavioral stress compared with that in vessels from control rats. Scanning electron microscopy of the endothelial surface of the septal coronary artery showed no difference between vessels from control and stressed BHR. These results indicate that behavioral stress impairs endothelium-dependent and nitric oxide-mediated coronary relaxation, but does not alter alpha1-adrenoceptor or endothelin-1-mediated contraction. By impairing coronary artery vascular relaxation, chronic exposure to behavioral stress may contribute to myocardial ischemia.

Soy isoflavones enhance coronary vascular reactivity in atherosclerotic female macaques

To examine the effects of soy phytoestrogens on coronary vascular reactivity in atherosclerotic male and female rhesus monkeys. A prospective, randomized, blinded, controlled study. Comparative Medicine Clinical Research Center of an academic medical center. Twenty-two young adult rhesus monkeys with pre-existing diet-induced atherosclerosis. Monkeys were fed soy-based diets for 6 months identical in composition, except that the isoflavones were extracted from one flow-isoflavone) and intact in the other (high-isoflavone). Quantitative coronary angiography was performed at the end of the study period. Females in the low-isoflavone group under went a second angiography after an acute IV dose of genistein. Percent change in diameter of the proximal left circumflex coronary artery in response to intracoronary acetylcholine and nitroglycerin, compared with control diameter. Arteries from males constricted in response to acetylcholine. Arteries from females in the low-isoflavone group constricted (-6.2% +/- 2.8%, mean +/- SEM), whereas arteries from females in the high-isoflavone group dilated (6.4% +/- 1.2%, mean +/- SEM). Intravenous administration of genistein caused dilation in the previously constricting low-isoflavone females (3.3% +/- 2.8%). Like mammalian estrogens, dietary soy isoflavones enhance the dilator response to acetylcholine of atherosclerotic arteries in female monkeys.

5‐HT1D receptor agonists and human coronary artery reactivity in vitro: crossover comparisons of 5‐HT and sumatriptan with rizatriptan and L‐741,519

1Rizatriptan (MK‐462, (N,N‐dimethyl‐2‐[5‐(1,2,4‐triazol‐1‐ylmethyl)‐1H‐indol‐3‐yl]ethylamine)) and its structurally related analogue L‐741,519 (N‐methyl‐4‐[5‐(1,2,4‐triazol‐4‐yl)‐1H‐indol‐3‐yl]piperidine) are novel 5‐HT1D‐receptor agonists. Rizatriptan has shown efficacy as an anti‐migraine agent in clinical trials. Since angiographic studies in patients have shown that sumatriptan (an established 5‐HT1D‐receptor agonist) can cause coronary artery vasoconstriction, we compared the effects of rizatriptan and L‐741,519 with those of 5‐HT and sumatriptan on endothelium‐denuded segments of human coronary artery in vitro. 2Coronary arteries were obtained from explanted hearts from patients undergoing cardiac transplantation (n=16 viable arteries from 13 males, 3 females, aged 38–68 years) and arterial segments (5–6 mm in length) were mounted in organ baths for isometric tension recording. Each segment was first exposed to 45mm KCl and then to 5‐HT (1 nm–100 μm). Concentration–effect curves to rizatriptan and sumatriptan (Study 1, n=6 or 7 arteries) or sumatriptan and L‐741,519 (Study 2, n=8 arteries) were then performed in a consecutive and random manner. The response to repeated application of 5‐HT was obtained in separate segments. 3One artery showed severe atheroma and was not included in the analysis. ANOVA showed that 5‐HT responsiveness varied significantly between arteries from different patients, but not between arterial segments from the same patient. Desensitization was seen consistently across all agonists but did not significantly affect inter‐agonist comparisons. 4There was graded effectiveness in the ability of the agonists to cause contraction with the rank order of Emax values being 5‐HTsumatriptan&gt;L‐741,519&gt;rizatriptan. In terms of EC50 values, L‐741,519 was significantly more potent than sumatriptan. 5The present study (using a ‘cross‐over’ experimental protocol) confirms our previous observation that rizatriptan is less effective than sumatriptan in causing contraction of human isolated coronary artery. Furthermore, it shows that the lower maximum contractile response to rizatriptan, compared with that of sumatriptan, is not merely the consequence of variability in response to 5‐HT1D‐ receptor agonists between patients or between segments from the same artery.

Porcine coronary artery pharmacodynamics in vitro evaluated by a new intravascular technique: Relation to axial stretch

A new intravascular balloon catheter-based technique, impedance planimetry and the wire-mounted isometric tension technique commonly employed to study vessel pharmacodynamics in vitro, were compared. Porcine left anterior descendent coronary artery reactivity to nifedipine was assessed and the influence of 20% axial stretch was investigated. There were no histological differences between segments where the impedance planimetry balloon had been inflated and untouched segments. EC 50 values differed significantly between the three procedures applied: The isometric method ( n = 7): 2.54 ± 0.44 · 10 −9 M; nonstretched arteries by the impedance planimetric method ( n = 7): 1.99 ± 0.40 · 10 −8 M; arteries 20% axially stretched ( n = 7): 2.00 ± 1.36 · 10 −7 M (isometric and nonstretched: p < 0.05; isometric and stretched: p < 0.001; nonstretched and stretched: p < 0.05). Maximal relaxant responses to nifedipine were 91.8 ± 2.1% (isometric method), 105.1 ± 2.3% (nonstretched), and 104.9 ± 7.7% (stretched) (ANOVA, p = 0.11). In stretched arteries, the initial 12-min response to an increased dose of nifedipine was more rapid than the response of nonstretched arteries at a concentration of 1 · 10 −7 M ( p = 0.038) and had a nonsignificant tendeney toward a more rapid response at other concentrations. Resting tone could not be demonstrated and time control experiments showed no change in the maximal vessel response to potassium with any of the three methods. A new method in the evaluation of artery pharmacodynamics in vitro was presented. The study demonstrated that axial stretching of an artery has impact on the pharmacodynamic reactivity to nifedipine in porcine coronary arteries. Further studies are needed to evaluated the impact of the method on endothelial function.

Effect of gender and sex steroids on the contractile response of canine coronary and renal blood vessels.

The effect of gender, gonadal steroids, and antiandrogen/antiestrogen-treatment on the isotonic response of isolated preparations of the left anterior descending coronary artery (LAD), left circumflex coronary artery, and renal artery and vein of sexually mature dogs was investigated. The maximum isotonic response of the coronary and renal vasculature to the thromboxane A2 (TXA2)-mimetic U46619 was significantly greater, and the EC50 value was significantly lower in males as compared with females. Moreover, similar gender differences in the contractile response of the coronary vasculature to norepinephrine were observed. Pretreatment of male dogs with the antiandrogens flutamide or cyproterone acetate reduced the maximum contractile response of the LAD to the TXA2-mimetic. Pretreatment of female dogs with testosterone resulted in an increase in both the maximum contractile response and EC50 value to U46619. Antiestrogen treatment of female dogs with tamoxifen was associated with an increase in the maximum contractile response of the LAD to U46619. Estrogen pretreatment of male dogs decreased both the maximum contractile response and the EC50 value to U46619. Therefore, there is a sex difference in LAD and LCX contractile responses to both U46619 and norepinephrine. These results suggest that smooth muscle reactivity of dog coronary artery to the TXA2-mimetic U46619 may be susceptible to regulation by both androgens and estrogens. The observed gender differences in the catecholamine response may be similarly altered by changes in the hormonal milieu.

Methyltestosterone Does Not Diminish the Beneficial Effects of Estrogen Replacement Therapy on Coronary Artery Reactivity in Cynomolgus Monkeys

The objective of this study was to determine if methyltestosteone attenuates the effects of estrogens on the vascular reactivity of mildly atherosclerotic coronary arteries in surgically menopausal female monkeys. Impaired vasodilation is an early indicator of endothelial dysfunction, and the administration of estrogen improves the vasodilator response. Thirty-six adult female cynomolgus monkeys were ovariectomi/ed and fed an atherogenic diet for 16 weeks. During this time they received oral treatment with either (a) placebo, (b) esterified estrogens, or (c) esterified estrogens + methyltestosterone. Quantitative coronary angiography was used to measure the percent change in diameter of the left circumflex coronary artery in response to intracoronary infusions of control solution (5% dextrose) and acetylcholine (10-6 mol/liter). Coronary arteries of control (placebo-treated) animals constricted after acetylcholine infusion [-4 * 1.5% (mean ± SEM)]. Treatment with esterified estrogens alone or with methyltestosterone resulted in vasodilation (+4.4 ± 1.8% and +4.8 ± 1.8%, respectively) (p < 0.05 vs. control). These results indicate that treatment with esterified estrogens improves endotheliummediated vasodilation of atherosclerotic coronary arteries, and that the addition of methyliestosterone does not alter this response.

94368665 Effects of hormone replacement therapy on reactivity of atherosclerotic coronary arteries in cynomolgus monkeys

94368665 Effects of hormone replacement therapy on reactivity of atherosclerotic coronary arteries in cynomolgus monkeys

Regression of Atherosclerosis in Female Monkeys

The objective of this study was to determine the structural and functional changes that occur in the artery wall in response to plasma lipid lowering and hormone replacement in surgically postmenopausal monkeys with established coronary artery atherosclerosis. Eighty-eight surgically postmenopausal cynomolgus monkeys were fed an atherogenic diet for 24 months and were then allocated into 4 groups: group 1 (n = 20), a baseline necropsy group; group 2 (n = 25), a lipid-lowering diet only; group 3 (n = 22), lipid lowering plus conjugated equine estrogen treatment equivalent to 0.625 mg/d for a woman; and group 4 (n = 21), lipid lowering plus conjugated equine estrogen and medroxyprogesterone acetate treatment (equivalent to 2.5 mg/d for a woman). Treatment was for 30 months. Histomorphometric analysis of perfusion-fixed coronary arteries revealed that plaque size did not change significantly in any of the groups compared with group 1 (P > .20). Plasma lipid lowering permitted coronary artery remodeling to occur (coronary artery and lumen size doubled compared with group 1) (P < .05); however, hormone therapy did not augment remodeling. Quantitative angiographic analysis of coronary artery reactivity revealed that lipid lowering improved dilator responses to acetylcholine by 22 +/- 4% (P = .01) but not to nitroglycerin (P = .23). Hormone replacement did not further affect vascular reactivity to the agonists tested (P > .4), but addition of medroxyprogesterone acetate diminished the beneficial effects of conjugated estrogens on coronary flow reserve (P = .03). In summary, the major arterial sequelae of lipid lowering in female monkeys were artery and lumen enlargement and improved reactivity of large epicardial coronary arteries. Addition of hormone replacement to the dietary modification did not further augment these improvements, except for the dilator capacity of the coronary microcirculation.

814-3 Effect of Estradiol-17β upon Coronary Arterial Reactivity to Acetylcholine in Men with Coronary Artery Disease

Estradiol-17β (E) has been shown to improve exercise-induced myocardial ischemia and reverse acetylcholine (ACh)-induced coronary constriction in female patients with coronary artery disease (CAD). To test this latter effect in men we studied the effect of intracoronary administration of E (2.5 μ g) in 7 male patients with proven CAD (mean age 52 years). All patients underwent measurements of coronary artery diameter and coronary blood flow at rest, after control infusion and after infusion of ACh 1.6 and 16 μ g per min, using quantitative angiography and intracoronary Doppler flowmetry. Infusions were performed before and 20 minutes after the intracoronary administration of E. Coronary artery diameter was similar after either control or estradiol-17 β (mean ± SD; 2.9 ± 0.6 vs 2.8 ± 0.5 mm respectively. P = NS). E had no effect on the ACh-induced coronary constriction (ACh 1.6 μ g per min; 2.7 ± 0.3 vs 2.7 ± 0.2 mm, P = NS; ACh 16 μ g per min; 2.6 ± 0.3 vs 2.6 ± 03 mm, P = NS; post E vs pre E respectively). Likewise, E had no effect on basal coronary blood flow compared to control (77 ± 11 vs 75 ± 10 mL/min respectively, P = NS). E had no effect on the ACh-induced changes in coronary blood flow (ACh 1.6 μg per min; 95 ± 19 vs 90 ± 22 mL/min, P = NS; ACh 16 μg per min; 142 ± 27 vs 137 ± 39 mL/min, P = NS, post vs pre E respectively) Estradiol-17 β does not appearto attenuate acetylcholine-induced coronary constriction nor enhance acetylcholine-induced coronary blood flow in male atherosclerotic coronary arteries in vivo . This is in contrast to the effect of estrogen in menopausal females. This suggests that the coronary vasculature reacts differently to estrogen in males and females

Effects of hormone replacement therapy on reactivity of atherosclerotic coronary arteries in cynomolgus monkeys

Objectives. We attempted to determine whether continuous and cyclic medroxyprogesterone acetate modulates the effects of estrogen on dilation of atherosclerotic coronary arteries in surgically postmenopausal female monkeys.Background. Estrogen replacement in postmenopausal women preserves normal dilator responses of atherosclerotic coronary arteries. The effects of progestins on coronary artery reactivity have not been determined.Methods. Repeated quantitative coronary angiography was used to study the effects after 1 month of 1) no hormone replacement (control) or oral administration of 2) continuous conjugated equine estrogens, 3) cyclic high dose medroxyprogesterone acetate (MPA) given on days 16 to 26 of the month, 4) conjugated equine estrogens plus continuous low dose MPA, or 5) conjugated equine estrogens plus cyclic high dose MPA on endothelium-mediated dilation of atherosclerotic coronary arteries in 12 cynomolgus monkeys. Change in diameter of the left circumflex coronary artery was measured in response to intracoronary infusions of acetylcholine (10−6mol/liter per min) and nitroglycerin (15 μg/min).Results. Coronary arteries constricted during no hormone treatment (−8 ± 3% [mean ± SEMJ), dilated during conjugated equine estrogen treatment (+ 3 ± 1%, p < 0.05 vs. control) and constricted during cyclic MPA treatment (−3 ± 2%). Addition of cyclic or continuous MPA to the conjugated equine estrogen regimen inhibited acetylcholine responses by 50% (p < 0.05 vs. conjugated equine estrogens). There was no effect of treatment on vascular response to nitroglycerin (p > 0.05).Conclusions. Treatment with conjugated equine estrogens, but not MPA, augmented endothelium-mediated dilation of atherosclerotic coronary arteries. Addition of cyclic or continue as MPA to the conjugated equine estrogen regimen diminished endothelium-mediated dilation.

Pharmacological reactivity of human epicardial coronary arteries: characterization of relaxation responses to endothelium-derived relaxing factor.

1. Human epicardial coronary artery rings, freshly obtained from cardiac transplant patients, were examined for their responses to endothelium-derived relaxing factor (EDRF)-releasing agents. 2. Functional antagonism profoundly influenced relaxation responses in this tissue. Increasing force with concentrations of U46619 above 3 nM (40% of maximum contraction response) resulted in a reduction of the maximum response to four vasorelaxants which relax vascular smooth muscle via different mechanisms: the EDRF-releasing agents, substance P and bradykinin; the endothelium-independent nitro-vasodilator, sodium nitroprusside (SNP); and the beta-adrenoceptor agonist, isoprenaline. 3. Substance P, histamine, bradykinin and the Ca2+ ionophores ionomycin and A23187 all caused concentration- and endothelium-dependent relaxation in vessels pre-contracted with the thromboxane A2-mimetic, U46619 (3 nM) to an active force optimal for relaxation responses. Nifedipine (0.1 microM), added to prevent spontaneous contractions, had no effect or relaxation responses to substance P, bradykinin and histamine. 4. Substance P was the most potent of the EDRF-releasing agents examined and all agents except for bradykinin caused near-maximal relaxation. Bradykinin caused only 46.2% +/- 7.3% relaxation. Responses were abolished when the endothelium was removed and, except for histamine, were not significantly affected by indomethacin (3-10 microM, P > 0.05). Histamine (0.1-10 microM) caused a concentration-dependent contraction of arterial rings without endothelium. 5. The L-arginine analogues NG-nitro-L-arginine (L-NOARG, 0.1 mM) and NG-monomethyl-L-arginine (L-NMMA, 0.1 mM) both caused no further contraction in arteries precontracted with U46619 (3 nM) and were in general, poor inhibitors of responses to EDRF agonists. L-NMMA, but not L-NOARG,caused small but significant decreases in the maximum responses to substance P, bradykinin (18.5 +/- 6.9% and 27.6 +/- 10.9% relaxation with L-NMMA and L-NOARG, respectively), histamine and A23187 (P<0.05). The analogues had no effect on SNP responses.6. In conclusion, EDRF release in human isolated coronary artery is only poorly antagonized by the nitric oxide synthase inhibitors L-NOARG and L-NMMA. These results indicate that either the nitricoxide transduction pathway present in human coronary artery is different from that in other tissues or that another factor(s) (e.g. endothelium-derived hyperpolarizing factor) is also released in response to EDRF-releasing agents and augments the relaxation to nitric oxide.

Pharmacological reactivity of human epicardial coronary arteries: phasic and tonic responses to vasoconstrictor agents differentiated by nifedipine

1. Human epicardial coronary artery rings, freshly obtained from cardiac transplantation patients, commonly exhibited phasic contractile activity in vitro. This activity occurred either spontaneously or in response to vasoconstrictor stimulation. 2. Nifedipine pretreatment (1 nM-0.1 microM) reduced both types of phasic contractions in a concentration-dependent manner. At 0.1 microM nifedipine, spontaneous contractions were completely abolished, as were phasic contractions induced by U46619, endothelin-1 or 5-hydroxytryptamine (5-HT). 3. For U46619 (0.1-100 nM), the largest phasic contractions (amplitude peak to trough) occurred over the mid-range of concentrations used (1-10 nM). At higher concentrations (30-100 nM), phasic activity was reduced as the response reached a maximum. Estimated pEC50 values for the upper phasic and lower phasic curves were significantly different (8.71 +/- 0.13 versus 7.90 +/- 0.11; P < 0.05; n = 10). In the presence of nifidepine (0.1 microM), the purely tonic contraction curve to U46619 was similar to the lower phasic curve in the absence of nifedipine (pEC50 = 8.14 +/- 0.06, n = 10). Similar results were obtained for endothelin-1 (0.1-100 nM). 4. Responses to 5-HT (1 nM-3 microM) were more variable. The largest phasic contractions were spread unevenly throughout the concentration-response curve. In the presence of nifedipine (0.1 microM), the curve to 5-HT was significantly depressed in range but not sensitivity (pEC50) when compared with the phasic curves. 5. In conclusion, activation of dihydropyridine-sensitive voltage-operated Ca2+ channels mediated the phasic contractions commonly observed in human epicardial coronary arteries. These contractions amplified the contractile responses to low concentrations of vasoconstrictors. Inhibition of phasic activity by the Ca2+ channel antagonist, nifedipine, allowed the tonic vasoconstrictor profile of human isolated coronary artery to be determined which is important information for the accurate quantitative assessment of vasodilator responses in this tissue in vitro.

Ischemia and activated neutrophils alter coronary microvascular but not epicardial coronary artery reactivity

Activated neutrophils have been implicated in reperfusion injury and the no-reflow phenomenon of intramyocardial arterioles. This study tested the hypothesis that ischemia and activated neutrophils impair coronary endothelial and smooth muscle cell function of epicardial and intramyocardial coronary arteries. Alteration of smooth muscle and endothelial cell function in epicardial coronary arteries (3 mm diameter) and intramyocardial coronary arteries (0.3 mm diameter) was compared by means of a myograph after exposure to ischemia (epicardial, 160 minutes; intramyocardial, 30 minutes), activated neutrophils, and combined ischemia and activated neutrophils. Morphologic studies at the ultrastructural level were done by means of scanning electron microscopy. Epicardial coronary artery function was normal after ischemia, storage with activated neutrophils, and ischemia followed by storage with activated neutrophils. Intramyocardial artery function, however, was altered. Contraction to a 45 mmol/L concentration of potassium chloride after ischemia and storage with activated neutrophils was increased ( p = 0.06). Smooth muscle relaxation was significantly decreased after ischemia, but storage with activated neutrophils did not further decrease smooth muscle relaxation. Endothelium-dependent relaxation to bradykinin was significantly decreased after combined ischemia and incubation with activated neutrophils ( p < 0.05). Sensitivity to bradykinin was decreased after both ischemia alone ( p < 0.05) and activated neutrophils alone ( p < 0.05). Similar morphologic alterations were found in epicardial and intramyocardial arteries after ischemia. Activated neutrophils alone minimally damaged endothelial cells of nonischemic intramyocardial and epicardial arteries. Endothelial cells of both arteries exposed to ischemia alone showed evidence of ischemic damage, including endothelial cell blebbing, nuclear bulging, and appearance of large holes in the cell surface. Severe endothelial cell damage was found after combined ischemia and storage with neutrophils: total destruction of cells and exposure of the basal lamina. Endothelial damage, therefore, correlated with artery function in intramyocardial but not in epicardial arteries. These results indicate that ischemia is a prerequisite for severe neutrophil injury of intramyocardial artery endothelium-mediated relaxation. This may explain no-reflow phenomenon in arterioles concurrent with myocardial reperfusion injury. (J THORAC CARDIOVASC SURG 1994;108:648-57)

Determinants of coronary artery reactivity in premenopausal female cynomolgus monkeys with diet-induced atherosclerosis.

The purpose of this study was to identify determinants of coronary artery reactivity among premenopausal female monkeys. Estrogen replacement therapy in postmenopausal females modulates reactivity of atherosclerotic coronary arteries. However, no studies have evaluated the factors that modulate coronary artery reactivity among premenopausal females. Twenty-five adult premenopausal female monkeys were fed an atherogenic diet for 32 months. During this time, monkeys were housed in small social groups and determined to be socially dominant (associated with normal ovarian function) or subordinate (associated with impaired ovarian function). After 32 months, coronary artery vasomotor responses to intracoronary acetylcholine, nitroglycerin, and serotonin were assessed by computer-assisted quantitative coronary angiography. Coronary arteries of dominant monkeys dilated (+9 +/- 2%), whereas those of subordinate monkeys constricted (-6 +/- 2%) in response to acetylcholine (P < .05). There was no effect of social status on vascular response to nitroglycerin or serotonin (P > .10). Vascular responses to acetylcholine were independent of social status effects on plasma lipids, blood pressure, and atherosclerosis extent. The correlation between acetylcholine responses and plasma estradiol concentration measured on the day of angiography was r = .7 (P = < .01). Furthermore, dilation occurred only if plasma estradiol concentrations were greater than 60 pg/mL. Psychosocial factors and endogenous estrogen production are important modulators of acetylcholine-mediated dilation of atherosclerotic coronary arteries among premenopausal female monkeys.

Enhanced coronary vasoconstrictive response to serotonin subsides after removal of dietary cholesterol in atherosclerotic monkeys.

Constriction in response to serotonin is enhanced in the coronary arteries of atherosclerotic monkeys. The main objective of the present study was to determine whether abnormal responses to serotonin in atherosclerosis are reversed following removal of dietary cholesterol. In addition, we examined the effect of an atherogenic diet and reduction in dietary cholesterol on vascular responses to activation of ATP-sensitive K+ channels with aprikalim. Diameters of small coronary arteries were measured on the epicardial surface of the left ventricle in vivo by using stroboscopic illumination synchronized to the heart cycle to visually freeze the motion of the heart. Diameters were measured with a microscope-video system during topical application of two vasoconstrictor agonists, serotonin and the thromboxane mimetic U46619, and the vasodilator agonists aprikalim and nitroprusside. Responses were compared in normal (n = 9), atherosclerotic (n = 14; high-cholesterol diet), and regression (n = 8; high-cholesterol diet followed by normal diet) monkeys. Constriction of coronary arteries in response to serotonin was enhanced in monkeys on an atherogenic diet and was normal in regression monkeys. Vasoconstriction in response to U46619 and vasodilation in response to nitroprusside and aprikalim were not altered by atherosclerosis. Thus, abnormal vascular responses to serotonin in small coronary arteries of atherosclerotic monkeys without morphological evidence of disease can be reversed to normal by reducing dietary cholesterol.

2-Deoxyglucose-induced vasodilation and hyperpolarization in rat coronary artery are reversed by glibenclamide

The mechanisms responsible for coronary vasodilation during ischemia or hypoxia are poorly understood. It has recently been suggested that alterations in intracellular ATP may play a role in this response. We examined whether dilation of isolated coronary arteries in response to metabolic blockade by 2-deoxyglucose, which competitively inhibits glycolysis and glycogenolysis, was sensitive to glibenclamide, an inhibitor of ATP-sensitive potassium channels. Pressurized rat coronary arteries with myogenic tone dilated in response to 2-deoxyglucose by an endothelium-independent mechanism. The dilation was accompanied by a substantial hyperpolarization. Addition of glibenclamide partially reversed this vasodilation and abolished the hyperpolarization. We propose that ATP-sensitive potassium channels play a significant role in the dilator response to 2-deoxyglucose. This may have implications both for ischemia-induced coronary vasodilation and for the use of oral hypoglycemic agents in general.

Hydralazine Dilates Large Epicardial Coronary Arteries in Conscious Dogs Through an Endothelium-Independent Mechanism

In chronically instrumented conscious dogs, hydralazine (30-300 micrograms/kg) and nitroglycerin (NTG 0.03-10 micrograms/kg) dose-dependently dilated large epicardial coronary arteries. Simultaneously, hydralazine also dose-dependently dilated small coronary arteries, whereas a similar effect was observed only after NTG > 0.3 microgram/kg. When large coronary arteries were deendothelialized by a balloon angioplasty catheter, dilation of large coronary arteries in response to acetylcholine (ACh 0.3 microgram/kg) and to reactive hyperemia was reduced by 87 and 95%, respectively. In contrast, vasodilation of large coronary arteries induced by hydralazine and NTG was only minimally and similarly affected (-19% for both drugs). These findings demonstrate that in vivo hydralazine-induced dilation of large coronary arteries is endothelium independent.

Stretch revealed three components in the hyperpolarization of guinea-pig coronary artery in response to acetylcholine.

1. Membrane potential was recorded with intracellular microelectrodes from the smooth muscle of coronary arteries of guinea-pigs, and the responses to endothelium-derived relaxants were studied under a variety of conditions. 2. Stimulation of the endothelium with brief applications of acetylcholine or substance P evoked concentration-dependent hyperpolarizations that were complex in nature. A transient component, which is likely to result from endothelium-derived hyperpolarizing factor (EDHF), was followed by a slow component that resulted from the production of nitric oxide (NO) and a prostaglandin. 3. The ability of exogenous and endogenous NO and prostacyclin to hyperpolarize the membrane depended upon the smooth muscle being under stretch. Unstretched preparations responded to acetylcholine with only the transient component of hyperpolarization; NO and prostacyclin were without effect. 4. In stretched preparations exogenous NO and prostacyclin, and its synthetic analogue methyl prostacyclin (Iloprost), evoked hyperpolarization, and the slow component of the response induced by acetylcholine appeared. The amplitudes of these responses reached maximum when the tissues were stretched to the equivalent of approximately 50 mmHg. 5. From a resting membrane potential of -61 +/- 0.6 mV, exogenous NO and Iloprost hyperpolarized the smooth muscle to around -80 mV. The EC50 values for NO- and Iloprost-induced hyperpolarization were 2.6 x 10(-6) and 1.3 x 10(-8) M, respectively. 6. Coronary arterial smooth muscles from rats, rabbits and sheep also hyperpolarized in response to exogenous NO, although their sensitivities were less than those of preparations obtained from guinea-pigs. Iloprost hyperpolarized tissues from rabbits and sheep but not those obtained from rats. 7. It is concluded that the endothelial lining of coronary arteries can release three factors, EDHF, NO and prostacyclin, all of which can hyperpolarize the membrane of the smooth muscle. The relative proportions and significance of each factor depends on the amount of stretch, on the artery and on the species of animal.