Effect of Plasma Osmolality on Resistance to Blood Flow through Skeletal Muscle

The gastrocnemious-plantaris muscle group of the dog was pump-perfused at constant flow with fresh plasma from a donor dog. When the osmolality of the perfusing plasma was increased by adding sodium chloride, glucose, sucrose, mannitol, dextran, or urea, the resistance to flow through the muscle decreased. The decrease in resistance was proportional to the increase in plasma osmolality. When distilled water was added to the plasma to decrease the osmolality, the resistance to flow through the muscle increased in proportion to the decrease in osmolality. The response to most test substances persisted for at least 20 min. These data suggest a mechanism regulating blood flow in resting muscle that is sensitive to osmolar concentration differences.