EFFECTS OF POTASSIUM AND OUABAIN ON THE VASCULAR REACTIVITY TO NOREPINEPHRINE IN THE RAT MESENTERIC-ARTERY

In the perfused rat mesenteric vascular bed, the effects of potassium and ouabain on the vascular response to norepinephrine were studied. Neither changing the concentration of potassium (1.9 to 7.9 mM) nor adding ouabain (8.6x10-7 to 2.2x10-4 M) to the perfusate changed the basal pressure. A slight increase in the potassium concentration in the perfusate attenuated the vascular response to norepinephrine, and a slight decrease in the potassium concentration potentiated this response. Ouabain in the perfusate potentiated the vascular response to norepinephrine in a dose-related manner. The effect of potassium on the vascular response was inhibited in the presence of ouabain. In preparations in which vascular reactivity had been abolished by indomethacin and then restored by prostaglandin E2, the effects of potassium and ouabain on the vascular reactivity to norepinephrine were similar to those found in the untreated preparations. These results indicate that a slight change in potassium concentration in the perfusate can affect the vascular respose to norepinephrine by changing the activity of Na+-K+-dependent ATPase. It is also suggested that the potentiating effect of low potassium concentration on the norepinephrine response is, at least in the rat mesenteric vascular bed, not mediated by the synthesis of prostaglandin E2 in the vascular wall.