[Tonus of epicardial main arteries and dynamic stenosis]

Under physiologic conditions the tone of the epicardial coronary arteries plays a minimal role in the regulation and distribution of myocardial blood flow. However, under pathophysiologic conditions, especially in coronary heart disease, even small changes in tone may play an eminent role. A uniform mechanism for the induction of excessive coronary constriction and spasm is as yet not recognizable. It is probably a multifactorial event in which different, variable factors add to or potentiate each other. This constriction or spasm inducing chain can with certainty only be interrupted at one of its last links: prevention of an excessive activation of the smooth vascular contractile apparatus through a reduction of the activating calcium influx (calcium antagonists) or through an increase of the intracellular cGMP-content with nitrates (through a not yet identified relaxation procedure). In this brief review constriction-inducing or -potentiating factors are discussed in context with the "dynamic stenosis:" alpha-adrenergic and parasympathetic mechanisms, serotonin, histamine, prostanoids and leukotrienes, finally changes of endothelial factors. Under experimental conditions these factors may bring about a more or less pronounced coronary constriction. In animal experiments it is only possible in mini-pigs with experimental coronary atheromatosis or sclerosis (in combination with experimental endothelial damage) to induce spasm-like constrictions of the large epicardial arteries using histamine or serotonin. Under a variety of clinical conditions the importance of these factors for the induction of dynamic coronary stenoses was shown to be of potential significance.(ABSTRACT TRUNCATED AT 250 WORDS)