Na+, K+-ATPase Inhibitory Activity of Fractionated Urine during Changes in Dietary Sodium Intake in Man.

Na+, K+-ATPase inhibitory activity in urine fractionated by HPLC was quantified in 7 normotensive male subjects during changes in dietary sodium intake. Subjects were studied on free sedium intake for 2 days, on low sodium intake (2g/day) for 3 days, on high sodium intake (22g/day) for 4 days and subsequently on normal sodium intake (6g/day) for 2 days. Na+, K+-ATPase inhibitory activity in fraction 10 eluted with 17% acetonitrile by reverse-phase HPLC was 12.3±5.2%(mean±S. D.) on free sodium intake, 8.7±9.8% on the 3rd day of low sodium intake, 61.2±6.6% on the 4th day of high sodium intake, and 20.5%±0.7% on the 2nd day of the normal sodium intake. Changes in Na+, K+-ATPase inhibitory activity of fraction 10 were closely associated with those in urinary sodium excretion. These results suggest that an endogenous Na+, K+-ATPase inhibitor (s) which plays a physiological role in the control of sodium and water balance may exist in this particular fraction.