Vascular responses to catecholamine of the sinus node artery of the dog.

On the coronary circulation, the effect of catecholamines was disputed by many investigators, and there is general agreement that catecholamines increase the coronary blood flow. However, some researchers attributed this vasodilatation to myocardial stimulation and consequent metabolic vasodilatation rather than to direct action to the coronary artery1,2,3). On the other hand, ZUBERBUHLER and BoHR4) reported that epinephrine and norepinephrine caused contraction of the isolated coronary artery strips after beta-receptor blockade. Similarly DOUTHEIL et al.5), GAAL et al.6), and PARRATT7) have demonstrated alpha-receptor activity after induction of beta-receptor blockade in the anesthetized dog. Recently PITT et al.8) who investigated the coronary flow in the unanesthetized dog using chronically implanted electromagnetic flow transducers described both alphaand beta-receptor activities for catecholamines in coronary arteries. In the previous papers9,10), the present authors described the constant pressure perfusion of the sinus node artery. This artery, the outer diameter of which is from 0.5 to 1 mm and is a branch of the right coronary artery, runs on the surface of the right auricle to the sinus node area. The extravascular pressure exerted by myocardial contraction will be minimum among other coronary arteries because of thin atrial muscle and low atrial pressure. Furthermore occlusion of this artery induces a positive chronotropic response of the sino-atrial node due to a baroceptive response9), but never induces degenerative tissue damage. Then this artery is not like the ordinary coronary arteries which nourish myocardium, and may be considered as a specific coronary artery. In the present study, the authors investigated whether alphaand beta-adrenergic receptor activities could be demonstrated in this artery.