Blood flow distribution in rat muscles during preexercise anticipatory response

Previous work has suggested that preexercise "anticipatory" blood flow distribution in the muscles of rats is influenced by the intensity of the preceding conditioning or training program. The purpose of this study was to carefully control the conditioning programs for control, low-speed conditioned, and high-speed conditioned rats to determine the respective effects on preexercise mean arterial pressure (Pa), heart rate (HR), and blood flow distribution in muscles and other organs. Control (daily placement on treadmill, no exercise), low-speed conditioned (daily treadmill walking up a 12 degree incline at 15 m/min), and high-speed conditioned (daily treadmill galloping up a 12 degree incline at 50 m/min) rats were conditioned for 2-4 wk in their respective programs. On the experimental day, the circulatory variables were measured immediately before exercise by using the same preexercise regimen as during the conditioning sessions. Pa, HR, and blood flow distribution were the same in control and low-speed conditioned rats (P greater than 0.05). However, in high-speed conditioned rats, HR (+9%), Pa (+7%), and white gastrocnemius muscle (+46%) blood flow were higher than in controls (P less than 0.05). The higher white muscle flow was the result of the higher Pa and lower resistance to flow. These data demonstrate that specific changes in preexercise anticipatory blood flow distribution among muscles occur during exercise conditioning programs and that the changes are dependent on the intensity of the conditioning regimen. The mechanisms responsible for the adaptations are not known.