Improvement of reduced coronary vasodilatory response during reactive hyperemia by diltiazem

This study was performed to reconfirm transiently-reduced vasodilatory responses of the coronary artery in the reactive hyperemic period, and also to study whether an increase in calcium influx into the coronary smooth muscle accounts for the reduced coronary vasodilatory responses. Blood flow in the circumflex coronary artery was measured with an electromagnetic flow transducer in anesthetized open-chest dogs. Two successive occlusions for 3 to 7 s performed in pairs with a brief interval were accompanied by decreasing reactive hyperemia: the maximum reduction of reactive hyperemia appeared when the occlusion period was around 5 s with a 5-s interval. Around 5 s after the release of occlusion, excess arterial inflow almost equaled the blood flow debt incurred during the first occlusion. Pretreatment with diltiazem (150 micrograms/kg), a calcium entry blocker, significantly attenuated the reduction of coronary vasodilatory responses, but glyceryl trinitrate (nitroglycerin) did not affect the phenomenon of coronary reactivity. The results suggest that excess accumulation of calcium in the smooth muscle of small coronary arteries occurred during an early period of post-occlusion hyperemia, which resulted in a reduced vasodilatory reactivity of the vessels to the second ischemic stimulus.