Prolonged vasodilation following fatiguing exercise of dog skeletal muscle

Prolonged vasodilation follows 20- and 60-min periods of stimulation (4 twitches/s) of dog skeletal muscle with blood flow held constant at 23 plus or minus 2 ml/100 g per min. During stimulation isometric tension development fell 61 plus or minus 3%, and we have operationally defined this as fatiguing exercise. During stimulation vasodilation was maximum. Following stimulation vascular resistance returned to control with average half-times of 6.9 plus or minus 0.6 and 5.8 plus or minus 0.4 min after 20 and 60 min of stimulation, respectively. This prolonged vascular recovery following fatiguing exercise is an order of magnitude slower than vascular recovery following less severe exercise. The pressor response to an intra-arterial bolus of angiotensin (0.5 mug) is not depressed during prolonged vasodilation. Prolonged vasodilation does not appear to be closely linked to changes in tissue oxygen consumption. In addition, the changes in resistance can be dissociated from changes in K+, osmolality, and lactate production following fatiguing exercise. We conclude that prolonged vasodilation following fatiguing exercise is caused by a metabolic vasodilator substance which is yet to be identified.