HYPEROSMOLALITY AND VASODILATATION IN HUMAN SKELETAL MUSCLE

Exercise of the forearm muscles in man was found to cause a considerable increase of the osmolality in the venous effluent but no osmolar change in arterial blood, thus indicating a regional hyperosmolality in the working muscles. There was a relation between the degree of hyperosmolality during work and the extent of the exercise hyperemia (determined immediately after cessation of exercise). Experimental hyperosmolality of similar magnitudes, produced in the resting skeletal muscle by intra‐arterial infusion of hypertonic solutions of glucose, xylose, or mannitol, invariably elicited a dilatation of the resistance vessels, whereas there was no significant effect of isotonic infusion. Vascular resistance tended to decrease progressively with increasing osmolality. Furthermore, intramuscular deposits of Xe133 in the resting muscle were cleared more rapidly when the tracer was dissolved in hypertonic than in isotonic medium, indicating a hyperemia response also when the hyperosmolality primarily involved the extra‐vascular space. The results are discussed in relation to previous studies of the effects of hyperosmolality on skeletal muscle circulation in anesthetized animals and on vascular smooth muscle in vitro. The conclusion was reached that hyperosmolality can be one factor contributing to exercise hyperemia in man. © 1969 Scandinavian Physiological Society