Effects of extracellular potassium on the pressure response to noradrenaline in the perfused hindquarters of the rat.

1. The hindquarters of the rat were perfused with oxygenated Tyrode-Ficoll solution at constant flow and the blood pressure in the caudal artery was measured. All experiments were started with the resistance vessels maximally dilated (arterial pressure 20 mmHg). 2. Variations in the extracellular potassium concentration (from 0.5 mmol/l to 22 mmol/l) had no direct effect on the arterial pressure. 3. Noradrenaline in the range 1.6-17 mumol/l increased the arterial pressure in a dose-dependent manner at all potassium concentrations. 4. Variations in the potassium concentration within the physiological range did not affect the dose-dependent responses to noradrenaline.