Effect of Hypokalemia and Hypomagnesemia Produced by Hemodialysis on Vascular Resistance in Canine Skeletal Muscle

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Abstract
Hemodialysis was used to study the effect of an acute local decrease in plasma [K+] or [Mg2+] or in both on vascular resistance in skeletal muscle. A dialyzer was placed in the arterial supply of the collateral-free gracilis muscle of the dog and blood flow was held constant while measuring perfusion pressure. Pressure increased linearly with decreased [K+] down to 0.2 mEq/liter. A 50% decrease in [K+] produced a 12% increase in resistance. Prolonged hypokalemia produced a sustained increase in perfusion pressure and a decreased responsiveness to close arterial injection of norepinephrine. Removal of up to 84% of the plasma Mg2+ produced no effect, either alone or in conjunction with hypokalemia. When the potassium level of the perfusing blood was changed from normal to hypokalemic during the dilation brought on by simulated exercise, the resistance did not change. In addition, the magnitude of the resistance changes seen during exercise were much greater than could be induced by local changes in plasma [K+] alone. It is concluded that hypokalemia produces active constriction of vascular smooth muscle. However, this study fails to lend support to the idea that potassium alone is responsible for exercise dilation.

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