Cardiovascular responses to voluntary and treadmill exercise in rats.

Male Sprague-Dawley rats (n = 12) were housed in activity wheels and familiarized with treadmill running 2 wk before they were instrumented with Doppler flow probes and a carotid catheter. Mean arterial pressure (MAP), heart rate (HR), mesenteric blood flow (BFmes), and iliac blood flow were determined during bouts of voluntary and treadmill exercise. One voluntary exercise bout (speed = 33 +/- 2 m/min, duration = 26 +/- 5 s) from each rat was selected to compare with 30 s of treadmill exercise at 30 m/min. Voluntary exercise produced increases in MAP (7 +/- 3 mmHg) and HR (63 +/- 7 beats/min) that were significantly less than the increases of 21 +/- 5 mmHg and 95 +/- 9 beats/min, respectively, with treadmill exercise. Voluntary exercise caused an immediate reduction in BFmes of 32 +/- 6%, whereas treadmill exercise produced a significantly greater reduction of 57 +/- 4%. Voluntary and treadmill exercise caused similar increases in iliac blood flow of 112 +/- 15 and 169 +/- 31%, respectively. The patterns of cardiovascular adjustments to the initiation of voluntary exercise are similar to those observed at the initiation of treadmill exercise; however, MAP, HR, and BFmes responses were significantly greater with treadmill exercise.