Effects of Exercise Training on Coronary Reactive Hyperemia and Blood Flow in the Dog

The reactive hyperemic responses to 10-s coronary occlusions were studied in seven sedentary-control (C) and eight exercise-trained (T) anesthetized dogs, with electromagnetic flowmeters placed on the left anterior descending coronary artery. Radiolabeled microspheres (9 +/- 0.8 micron) were used to measure resting coronary flow per gram and to study the effects of isoproterenol infusion (ISO) (1 mg/kg-min) on total and regional coronary flow. Base-line coronary flow per 100 g was significantly greater in the T dogs (122 +/- 7) than in C dogs (100 +/- 4). During ISO, T and C coronary resistances did not differ significantly, whereas the effects of ISO on total and regional coronary flow were quite different in T dogs as compared to C dogs. C and T hyperemic flow debt repayments did not differ significantly; however, the peak reactive hyperemic flow in T dogs (344 +/- 12%) was significantly greater than the control (306 +/- 10%). Since resting coronary flow per gram was greater in T dogs, the greater peak reactive hyperemic flow implies that T dogs have an increased coronary reserve. Although the mechanisms involved are unclear, the results of this study indicate that chronic exercise training may have beneficial effects on coronary physiology.