Acute volume expansion in humans releases a factor which inhibits the vascular Na+-K+ pump

The authors previously observed increased Na+-K+ pump inhibitory activity in the plasma of low renin essential hypertensive unselected with respect to renin status. The present experiments were done to determine the effect of acute volume expansion on plasma Na+-K+ pump inhibitory activity in normotensive subjects. The data show that acute volume expansion increases vascular Na+-K+ pump inhibitory activity in plasma, suggesting that the increased level of this inhibitory activity in low essential hypertensives is probably volume dependent. The unique feature of this study is the use of vascular tissue for the bioassay.