Metabolic factors in peripheral circulatory regulation.

The old and recent literature bearing on the role of metabolic factors in exercise hyperemia has been reviewed. Two general conclusions have gradually emerged over the years. First, no one factor is by itself a sufficient explanation for the hyperemia. Second, the contributions of the various factors appear to change with time of exercise. While additional temporal studies are needed to firmly establish more specific conclusions, those now available suggest that factors related to skeletal muscle cell depolarization initiate the hyperemia while factors related to oxygen consumption in excess of oxygen delivery contribute more to the maintenance of the hyperemia. For example, the potassium that leaves the skeletal muscle cell on depolarization appears to contribute more to the initiation of the hyperemia than to its maintenance. Hydrogen, on the other hand, appears to have little to do with initiation but may contribute to maintenance, at least with grades of exercise that reduce cellular oxygen tension. The picture that emerges from the review seems to be one of multiple factors acting in concert with a changing temporal pattern.