Characteristics of urine sodium and potassium after oral ingestion of solutions containing sodium and potassium which is isotonic to the physiological saline--a quantitative study.

The effects of orally ingesting 500 mL of four kinds of test solutions that were isotonic to physiological saline (i.e., containing sodium (Na) and potassium (K) as chloride with Na/K molar ratios of 1, 2, 3 and 4) on urine flow, Na and K excretions from Japanese male students were investigated. The subjects assembled at the National Institute of Nutrition the day before the oral ingestions, which were conducted three times for each subject. They were permitted to eat freely until 8:00 pm, and then the intake of food and drinks except tap water was prohibited until 10:00 pm. After that, no food or drinks except the test solution used, were permitted to be ingested until the end of the final collection of urine. Subjects were woken up at 7:00 am the next morning, at which time they emptied their bladder. At 8:00 am, after sampling control urine before ingestion, they ingested 500 mL of water, the physiological saline or one of the test solutions. Urine was collected every 30 min for 4 h after ingestion. Urine flow was significantly higher for those who drank solutions Na/ K = 1 and 2 than those who drank the saline (paired-t test), but that for those who drank solutions Na/K = 3 and 4 was not significantly higher. For those who drank solution Na/ k=2, urine Na was significantly higher than that of those who drank the saline 30 to 60 min after ingestion. An increase in urine flow after K ingestion may be an essential factor for K-induced Na uresis.