Kazuhiko Aikawa

Multiple endothelial injury in epicardial coronary artery induces downstream microvascular spasm as well as remodeling partly via thromboxane A2.

OBJECTIVES The study was undertaken to develop a coronary microvascular spasm model in pigs by repeated epicardial coronary artery endothelial injury. BACKGROUND The pathophysiologic mechanisms responsible for coronary microvascular spasm remain unclear, in large part because a suitable animal model has yet to be found. METHODS Balloon endothelial denudation was done just distal to the site of an implanted Doppler flowmeter in the left anterior descending coronary artery (LAD) every two weeks for a total of four times. Changes in LAD blood flow by intracoronary administration of vasoactive agents were assessed before each denudation. RESULTS In the epicardial LAD endothelial denudation pigs, decreases in LAD blood flow caused by acetylcholine were augmented. Before denudation, it was - 15 +/- 4%, and at week 8 (i.e., two weeks after the fourth denudation) it was -100% (i.e., zero flow [p < 0.01]). The LAD flow changes in response to 5-hydroxytryptamine (5-HT) changed from an increase to a decrease, accompanied by medial thickening of microvessels in the LAD perfusion area. These flow responses were observed without significant changes in LAD diameter. In contrast, the LAD blood flow responses to acetylcholine and 5-HT did not change throughout the experiment in pigs given aspirin and a thromboxane A2 (TXA2) synthase inhibitor orally. CONCLUSIONS This microvascular spasm model indicates that hypersensitivity to vasoactive substances in the microvascular beds as well as microvascular remodeling are brought about partly through TXA2. This model should be useful for examining the pathophysiology and treatment of microvascular angina.

Morphological and functional changes in coronary vessel evoked by repeated endothelial injury in pigs

OBJECTIVE We examined the morphological changes induced by repeated endothelial denudation in coronary artery (CA), as well as functional changes in the endothelium-dependent and smooth muscle responses to various vasoactive agents during the process of intimal thickening. METHODS We observed vascular responses in denuded and non-denuded portions of pig CA while being fed a normal diet (n = 11, N group) or 2% cholesterol diet (n = 25, C group) to intracoronary acetylcholine (ACh), 5-hydroxytryptamine (5-HT), substance P (SP), and isosorbide dinitrate (ISDN) with and without the nitric oxide synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg i.v.) over a period of 8 weeks. Balloon endothelial denudation of the left anterior descending CA was carried out every 2 weeks. RESULTS In N group, maximum vasoconstriction was obtained with ACh 2 weeks after the first denudation [26 +/- 5% vs. 1 +/- 1% pre-denudation, p < 0.05]. L-NAME did not affect ACh-induced CA diameter changes. Thereafter, the response to ACh was attenuated by repeated denudation in N groups. However, the degree of 5-HT-induced CA narrowing at the denuded portion increased from 7 +/- 4% (0 week) to 88 +/- 8% (8 weeks) (p < 0.05). The changes resulted in severe myocardial ischaemia, and suggested that endothelium-dependent vasodilation was progressively attenuated while hyperreactivity of vascular smooth muscle simultaneously increased. Vasodilation induced by SP was attenuated somewhat, but ISDN-induced vasodilation was preserved. Although mild hypercholesterolaemia was induced in C group, the vascular responses to these vasoactive agents did not differ from those of N group. CONCLUSIONS Repeated CA endothelial injury and regeneration induce the change of morphology and vascular reactivity in the denuded portion regardless of atherogenic diet. This study strongly suggests that intimal thickening caused by repeated endothelial injury and regeneration induces specific vascular responses to vasoactive agents. Moreover, it is also suggested that during the progression of intimal thickening, increased vascular smooth muscle contraction and decreased endothelium-dependent dilation appear in a stimulus-dependent manner, often leading to severe coronary vasoconstriction accompanied with definitive ECG ST change.

Effects of antioxidants on coronary microvascular spasm induced by epicardial coronary artery endothelial injury in pigs.

ObjectivesThe effect of oxidative stress on coronary microvascular disease is unknown. We investigated whether chronic administration of ascorbic acid (ASC) or glutathione (GSH) prevents microvascular dysfunction and remodeling induced by upstream repeated coronary artery endothelial injury. MethodsBalloon endothelial injury was repeated at the left anterior descending coronary artery (LAD), just distal to an implanted flow meter, every 2 weeks for 6 weeks in pigs. Changes in LAD blood flow induced by acetylcholine (ACh) and 5-hydroxytryptamine were assessed before each endothelial injury and at 8 weeks after the first endothelial injury in pigs without treatment (endothelial injury group, n=12) and in pigs treated with oral ASC (3 g/day) (ASC group, n=12) and ASC (3 g/day) plus GSH (1 g/day) (ASC+GSH group, n=12). ResultsIn the endothelial injury group, reduced blood flow in response to ACh was augmented from a decrease of 18±17% to a decrease of 100% (that is, zero flow, 8 weeks, P<0.01), accompanied by an increase of ascorbyl free radicals (AFRs) in coronary sinus blood. In contrast, in the ASC+GSH group, blood flow response to ACh was altered to a decrease of 45±17% (8 weeks, P<0.01 compared with the endothelial injury group), coronary sinus blood AFRs did not change (8 weeks, 21.4±12.5 signal intensities, P<0.01 compared with the endothelial injury group) and the rate of platelet aggregation induced by adenosine diphosphate was small (8 weeks, 56±17%, P<0.01 compared with the endothelial injury group). ConclusionsChronic administration of antioxidants suppressed microvascular hypercontraction, suggesting that it may be a promising therapeutic strategy for treating coronary microvessel disorders, including microvascular angina.

Repeated epicardial coronary artery endothelial injuries lead to a global spontaneous coronary artery spasm.

ObjectivesThis study was conducted to develop a spontaneous coronary spasm model. Materials and methodsBalloon endothelial denudation was carried out in the epicardial left anterior descending coronary artery (LAD) every 2 weeks, for a total of four times, in 12 pigs. Changes in the denuded site diameter and LAD blood flow caused by acetylcholine or serotonin were assessed before each denudation and at week 8. Blood pressure, electrocardiogram (ECG) from the LAD area and LAD blood flow were monitored continuously in conscious and unrestrained pigs. ResultsSpontaneous ECG ST depression with a decrease in LAD blood flow appeared at around 2 weeks. In accordance with this, 0.5 μg/kg acetylcholine induced similar ECG and LAD blood flow changes without denuded site narrowing, suggesting microvascular spasm. Thereafter, ECG ST depression or elevation by serotonin via a denuded site spasm was found after 6 weeks and spontaneous ECG ST changes due to epicardial coronary artery spasm were observed. ConclusionEpicardial coronary artery endothelial injury may induce spontaneous vasospasticity in the downstream coronary microvessels as well as in the denuded portion, suggesting functional abnormality through the entire coronary arterial tree.