Prostaglandin and histaminergic mediation of prolonged vasodilation after exercise

An extended period of recovery of vascular resistance, far outlasting the recovery period of oxygen consumption, follows exercise of dog skeletal muscle when flow is restricted relative to the intensity of the exercise pattern. The duration of this postexercise prolonged vasodilation is graded and is related to the blood flow, duration of muscle stimulation, fatigue of the muscles, and total muscle tension development. To test whether prolonged vasodilation is mediated by prostaglandins or histamine, the prostaglandin synthetase inhibitors indomethacin or meclofenamate and the antihistamine tripelennamine were administered intravenously to anesthetized dogs between two 20-min exercise bouts of the anterior calf muscles at 4 twitches/s. Blood flow was held constant at approximately 20 ml 100 g-1 min-1, typically resulting in a venous O2 content below 2.0 ml/100 ml during exercise. The duration of vascular resistance recovery was evaluated by measuring the time at which vascular resistance returned to 90% (t90) of the recovery level (mean +/- SE). All the drugs caused a significant decline in the t90, but none reduced the recovery time to that following free-flow exercise, where the t90 is less than 1 min and the return of vascular resistance parallels the return of oxygen consumption to control. Thus, prostaglandin and/or histamine release may be at least partially responsible for prolonged vasodilation.