Smooth muscles from spastic coronary artery segments show hypercontractility to histamine

Mechanisms of Coronary Artery Spasm

Recent clinical trials have highlighted that percutaneous coronary intervention in patients with stable angina provides limited additional benefits on top of optimal medical therapy. This has led to much more attention being paid to coronary vasomotion abnormalities regardless of obstructive or non-obstructive arterial segments. Coronary vasomotion is regulated by multiple mechanisms that include the endothelium, vascular smooth muscle cells (VSMCs), myocardial metabolic demand, autonomic nervous system and inflammation. Over the years, several animal models have been developed to explore the central mechanism of coronary artery spasm. This review summarises the landmark studies on the mechanisms of coronary vasospasm demonstrating the central role of Rho-kinase as a molecular switch of VSMC hypercontraction and the important role of coronary adventitial inflammation for Rho-kinase upregulation in VSMCs.

Vasospastic Angina: A Contemporary Review of its Pathophysiology, Diagnosis and Management

Nearly 40% of patients presenting to the catheter laboratory with angina have non-obstructed coronary arteries (ANOCA), an umbrella term that encompasses distinct pathophysiological entities, such as coronary artery spasm. Coronary artery spasm leads to sudden reversible coronary flow attenuation, which clinically manifests as vasospastic angina (VSA). VSA is associated with poor quality of life and an increased risk of major adverse cardiac events. However, the pathophysiological mechanisms underlying this phenomenon are incompletely understood, which has resulted in limited therapeutic options for patients afflicted with this condition. The past decade has seen a surge in new research being conducted in the field of ANOCA and VSA. This review article provides a comprehensive summary of the underlying pathophysiological mechanisms of VSA and the current therapeutic options. We also appraise the current diagnostic approach in patients with suspected VSA.

Our animal model of coronary spasm--my personal view

We developed an animal model of coronary spasm in swine, similar to coronary spasm in patients with variant angina based on the angiographic findings. In this animal model, an impairment of endothelium dependent dilatation appeared to play a minor role while the hypercontraction of the medial muscle cells by histamine and serotonin at the spastic site played a major role in the induction of coronary spasm. In Göttingen male miniature swine receiving focal endothelial denudation, moderate hypercholesterolemia and X ray irradiation, the abrupt, severe and prolonged coronary spasm resulted in a sudden progression of organic coronary stenosis mainly due to intraplaque hemorrhage and also in acute myocardial infarction.

Cellular and molecular mechanisms of coronary artery spasm: lessons from animal models

Coronary artery spasm plays an important role in the pathogenesis of a wide variety of ischemic heart diseases, especially in the Japanese population. Because coronary artery spasm can be induced by a variety of stimuli with different mechanisms of action, the occurrence of the spasm appears to be due to the local hyperreactivity of the coronary artery rather than to an enhanced stimulation with a single mechanism of action. Several lines of evidence indicate that coronary artery spasm is caused primarily by smooth muscle hypercontraction whereas the contribution of endothelial dysfunction may be minimal. In order to elucidate the cellular and molecular mechanisms of the spasm, porcine models of the spasm were developed. In the first model with balloon injury and high-cholesterol feeding, a close topological correlation between the early atherosclerotic lesions and the spastic sites was noted, whereas in the second model with an inflammatory cytokine the potential importance of coronary inflammatory changes, especially at the adventitia, was noted. Subsequent studies in vivo and in vitro demonstrated that protein kinase C (PKC) and Rho-kinase are substantially involved in the intracellular mechanism of the spasm, resulting in increases in the mono- and diphosphorylations of myosin light chain (MLC). Furthermore, molecular biological analyses demonstrated that Rho-kinase is upregulated at the spastic site (at all levels, including mRNA, protein, and activity), resulting in the inhibition of MLC phosphatase through the phosphorylation of its myosin binding subunit and thereby causing the increase in MLC phosphorylations. Preliminary results also suggest that the long-term inhibition of Rho-kinase is effective in inhibiting the development of arteriosclerotic vascular lesions in several porcine models. Thus, Rho-kinase could be regarded as a novel therapeutic target for coronary arteriosclerosis in general and coronary artery spasm in particular.

Augmented agonist-induced Ca(2+)-sensitization of coronary artery contraction in genetically hypertensive rats. Evidence for altered signal transduction in the coronary smooth muscle cells

The Ca2+ responsiveness of vascular smooth muscle myofilaments is not unique: it is increased during neuro-humoral activation and decreased during beta-adrenergic stimulation. In this study we tested whether an augmented Ca2+ responsiveness of smooth muscle myofilaments may contribute to the increased coronary tone observed in hypertension using beta-escin-permeabilized coronary arteries from 3-mo-old stroke-prone spontaneously hypertensive rats (SHRSP) and their age matched normotensive reference strain (WKY rats). In intact coronary arteries, the response to 5-hydroxytryptamine (5-HT) but not to KCl was larger in SHRSP than in WKY rats. In beta-escin permeabilized coronary arteries in which the receptor effector coupling is still intact, 5-HT enhanced force at constant submaximal (Ca2+) (pCa 6.38) to a greater extent in SHRSP. The Ca2+ sensitizing effect of 5-HT was mimicked by GTP gamma S (0.01-10 microM); again this effect was larger in SHRSP. In the absence of 5-HT or GTP gamma S the Ca2+ force relation was similar in both groups. Forskolin induced relaxation at constant submaximal (Ca2+). This desensitizing effect was smaller in SHRSP than in WKY rats. In conclusion, this study shows that intracellular signalling pathways involved in modulating the Ca2+ responsiveness of coronary smooth muscle myofilaments are altered in the genetically hypertensive animals favoring a hypercontractile state in the coronary circulation.