Reflex regulation of the circulation after stimulation of cardiac receptors by prostaglandins.

Prostaglandins (PGs) are potent vasoactive substances that may participate in the control of coronary blood flow, platelet aggregation, and inflammation. An important action of PGs may be the stimulation of c fibers in general and vagal cardiac c fibers in particular. The Bezold-Jarisch reflex after intracoronary injection of Veratrum alkaloids is very similar to the vagal bradycardia elicited by stimulation of cardiac PG synthesis or injection of prostacyclin (PGI2). The characteristic features of this reflex are 1) stimulation of c fibers, 2) inferoposterior wall location of receptors, 3) vagal afferents, 4) vagal efferents to the heart, 5) sympathetic efferents to peripheral blood vessels, and 6) interaction with other reflexes. Vagal cardiac c fibers are activated by intracoronary injections of PGI2 or arachidonic acid, resulting in a vagal reflex bradycardia and hypotension due to withdrawal of peripheral alpha-adrenergic tone to resistance vessels. The cardiac receptors are located predominantly in the inferoposterior wall of the left ventricle. When stimulated by PGs, cardiac receptors may also modify the regulation of arterial pressure by the baroreflexes, altering the inverse relationship between systemic arterial pressure and heart rate. Thus, there is a striking parallelism between the veratridine-induced Bezold-Jarisch reflex and PG-induced cardiac reflexes, although the physiological and clinical significance of these reflexes remains to be determined.