The Potassium Ion as a Vasodilator during Muscular Exercise

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Abstract
Calf muscles of cats were perfused with blood at constant flow rates. Tissue volume, blood flow, arterial and venous pressures were measured. Exercise was imitated by intermittent contractions of the muscles. During contractions the potassium concentration of the venous plasma from the calf increased by up to 100 per cent. Potassium salts infused intra‐arterially at low rates dilated the vessels. It was calculated that the potassium released during exercise directly explains 25 to 65 per cent of the dilatation during exercise, the percentage being smallest when dilatation was slightest. There is presumably a diffusion gradient for potassium between tissue and blood with consequent underestimation of the role of the potassium ions, particularly when the dilatations are only weak. Therefore, 65 per cent probably comes closest to the true value of the proportion of the dilatation due to the potassium ions.Potassium infusions produced the same vascular response as exercise: a decrease of flow resistance was accompanied by a proportionate increase of the capillary filtration coefficient without signs of any increase in capillary permeability or dilatation of the capacitance vessels. Potassium is the only dilative substance hitherto found to produce exactly the same response as exercise.