The Effects of Hyperosmolarity on Intact and Isolated Vascular Smooth Muscle. Possible Role in Exercise Hyperemia

Abstract

Skeletal muscle exer-cise was associated with a pronounced increase of regional osmolarity. Intra-arterial infusion of hypertonic glucose or xylose solutions into resting skeletal muscle at rates producing similar changes in regional osmolarity elicited a pattern of vascular response resembling that during work. The extent of the evoked resistance vessel dilatation was only slightly below that seen in exercise. This dilatation seemed to be due to an inhibition of vascular smooth muscle tone. The mechanisms responsible for this inhibition were elucidated by recording electrical and mechanical activity in isolated vascular smooth muscle. Increased osmolarity exerts a ''negative chronotropic'' effect on the muscle by inhibiting myogenic pacemaker activity, which could be partly accounted for by hyperpolarization due to an increased gradient of internal K+ concentration/external K+ concentration. Hyperosmolarity of a high degree also interferes with propagation and with excitation-contraction coupling. A possible role of osmotic factors in exercise hyperemia is discussed.