Coronary flow, myocardial oxygen consumption, and exercise training in dogs.

Changes in coronary blood flow (CBF) and myocardial oxygen consumption (MVO2) were measured in 17 conscious dogs during submaximal exercise and before and after exercise training. The CBF responses to atrial pacing and a 10-s occlusion were measured in the resting animals. With atrial pacing at 240 beats/min, the change in CBF from resting values increased significantly (12.8 +/- 1 to 15.2 +/- 3 cm/s), reactive hyperemia response was decreased (463 +/- 55 to 328 +/- 52%), and CBF during submaximal exercise was reduced by the end of the 4th or 5th wk of training. These changes persisted for the duration of the training program. When the animals were trained, the CBF response to submaximal exercise was the same as in the untrained condition. Exercise MVO2 did not change with training, but oxygen extraction increased (80 +/- 1 to 83 +/- 1%). These results indicate that changes in the coronary vascular bed occurred very early in the training program and may be explained by either an autonomic nervous system change in control of coronary flow or a change in the anatomic architecture of the bed.