Myogenic Response of Resistance Vessels and Precapillary Sphincters in Skeletal Muscle during Exercise

Capillary filtration coefficient (CFC), reflecting precapillary sphincter tone, and venous outflow of cat lower leg muscle were observed at various transmural pressures before and during muscle work. Increasing transmural pressure in resting muscle 30 mm Hg caused a 35 per cent decrease in CFC, indicating increased tone of precapillary sphincters and, on the average, no change in blood flow, indicating that the increased active tone of resistance vessels closely balanced passive distention. During exercise at 1 twitch/sec, elevating transmural pressure decreased CFC by 50 per cent and increased flow 38 per cent indicating that while precapillary sphincters were still responsive, metabolic demand caused the resistance vessels to behave passively. At 4 twitches/sec the active response of the precapillary sphincters was present, although less marked, whereas the passive behaviour of the resistance vessels was even more pronounced than at 1 twitch/sec. Myogenic autoregulation of filtration exchange via alteration of precapillary sphincter tone may be an important factor preventing gross edema in the legs of upright man during exercise.