Vagal inhibitory effects on peripheral circulation in acute coronary occlusion

The reflex adjustments of the peripheral circulation in response to acute coronary occlusion were studied in anesthetized dogs with isolated vascular beds perfused at constant flow. Coronary occlusion caused significant increases in perfusion pressure which averaged 27 +/- 4 mmHg in the hindlimb, 19 +/- 8 mmHg in skeletal muscle, and 13 + 5 mmHg in the mesenteric artery. These responses were less than half those caused by a similar decrease in aortic pressure obtained with hemorrhage. Coronary occlusion caused no significant changes in renal and paw circulations, while marked vasoconstriction resulted from hemorrhage. When aortic pressure was maintained constant throughout the duration of coronary occlusion, there was a significant vasodilatation in all beds studied. After vagotomy, coronary occlusion caused a constrictor response similar in magnitude to that caused by hemorrhage in each vascular bed and the dilator responses to occlusion at constant aortic pressure were abolished. Both constrictor and dilator changes were prevented by alpha-adrenergic blockade. Mechanical distension of the left ventricle in four dogs with carotid sinus nerves cut caused a significant reflexdilatation in the hindlimb. Thus, coronary occlusion initiates an inhibitory reflex mediated by vagal afferents which opposes peripheral vasoconstriction most effectively in the renal and paw circulations.