BENEFICIAL EFFECTS OF POTASSIUM ON BLOOD PRESSURE: A NOVEL MECHANISM LINKED TO THE DISTINCTIVE CIRCADIAN RHYTHM OF URINARY POTASSIUM EXCRETION

Dietary K supplementation is known to reduce blood pressure (BP) but the mechanism is not yet elucidated. We have previously shown that a low urine flow rate (V) during the day (D) (possibly due to excessive vasopressin action) is accompanied by a reduced ability to excrete Na and is associated with a higher BP and/or a reduced nocturnal dipping. We reanalyzed relationships between excretion (exc) of K or Na, and V during D (16 h) and N (8 h) in 141 young normotensive adults on their normal diet (data from M. Weinberger, Indianapolis). With increasing 24 h K exc (reflecting K intake), K exc increased mostly during D (slope 1.40, r = 0.988) but only modestly during N (slope 0.19, r = 0.397) suggesting that K is excreted quickly after its ingestion. For a 3‐fold higher 24 h K exc, V was 1.93‐fold higher during D but only 1.27‐fold higher during N. In contrast, for a 3‐fold higher 24 h Na exc, VD and VN increased almost equally (x 1.67 and 1.50). In rat experiments, a selective increase in dietary K (x 3.5) doubled V in the active period (p < 0.001) with no change in the resting period. This effect of K on V is likely due to the limited capacity of the kidney to secrete and thus to concentrate K in the urine. These results suggest a novel mechanism for the beneficial effects of K on BP. By increasing V selectively during D, K could accelerate Na exc and thus reduce body fluid volume. Separate D and N urine collection during K supplementation will be necessary to confirm this hypothesis.