ABSTRACT
All elasmobranchs and about one-third of the teleosts studied have a well-developed coronary system. In species with a coronary system, there is a large inter-species variation in the proportion of the myocardium that is supplied, with a correlation between activity level and dependence on a coronary system. In fish, most of the knowledge about the control of the coronary circulation stems from in situ or in vitro work with only a few recent in vivo studies. In salmonids, about one percent of cardiac output is returned to compact myocardium through the coronary circulation. It has been shown that, as in mammals, the coronary circulation is compromised by the mechanical work of the heart and peak coronary flow occurs during diastole. The control systems involved in the regulation of the coronary vascular resistance changes include both neuronal and humoral components. As in mammals, there are alpha- and beta-adrenoceptors located in the coronary circulation and a cholinergically mediated vasodilatation has been described. ATP, ADP and prostaglandins are probably also involved in the control of the vascular resistance, and there is evidence that local metabolites also have a strong influence on the blood flow through the coronary system.