1. An assessment was made of the extent sodium (Na) and potassium (K) intake can be estimated from Na, K and creatinine (Cr) content of a second morning voiding urine (SMU) specimen collected within 4 h after the first voiding upon awakening but before breakfast in 159 clinically healthy, free-living individuals (20-79 years). The SMU and the rest of 24 h urine specimens for a 3-5 day period were collected. 2. The following equations for estimating 24 h urinary Na (24HUNaV) and K (24HUKV) excretions were developed, and the accuracy and the reliability of these equations were evaluated. Estimated value of 24HUNaV (mEq/day) = 16.3 square root of XNa; estimated value of 24HUKV (mEq/day) = 7.2 square root of XK, where XNa (or XK) = SMUNa (or SMUK)/SMUCr x predicted 24 h urinary Cr excretion. 3. Highly statistically significant correlations were detected between the values estimated and measured for both Na (r = 0.728, P < 0.001, n = 159) and K (r = 0.780, P < 0.001, n = 159). 4. These equations were applied to Group 1 subjects, who collected the urine for a single day, and to Group 2, for 3 days. The correlation coefficients between the values estimated and measured for Na and K were 0.531 and 0.443 in Group 1, and 0.821 and 0.590 in Group 2, respectively. No statistically significant differences were observed. 5. The SMU specimens provide a satisfactory alternative to both 24HUNaV and 24HUKV in adults for extensive epidemiological surveys but also for clinical application.
Information regarding daily intake of sodium (Na) is useful for both normotensive and hypertensive subjects. We measured urinary excretion of sodium (U-Na) and urinary excretion of potassium (U-K) to estimate daily salt intake in a cohort of health screening subjects in Okinawa, Japan. Urine samples were obtained from 2,411 subjects (1,554 men and 857 women) who were examined on a half-day dry-doc at the Okinawa General Health Maintenance Association (OGHMA). Four hundred and one subjects were examined twice, once between September and November in 1997, and once between September and November in 1998. The mean U-Na was 182 mEq/day for men and 176 mEq/day for women. The mean U-K was 54 mEq/day for men and 50 mEq/day for women. U-Na was higher in young men, and U-K was lower in young women. In both men and women, smokers had a significantly lower Na excretion compared to nonsmokers. Subjects treated for hypertension had a significantly lower Na excretion (173 mEq/day) compared to subjects not treated for hypertension (192 mEq/day). Our findings suggest that Na excretion in screened subjects in Okinawa is lower than the national average. Sodium excretion, however, was higher in young men than in elderly subjects, and K excretion was lower in young women than in elderly subjects. Both trends are disadvantageous for controlling hypertension.
The circadian profiles of D-alanine (Ala) amounts in human serum and urine have been clarified using a two-dimensional HPLC system combining a microbore reversed-phase C18 column and a Pirkle-type enantioselective column. The two-dimensional HPLC system enables the determination of trace amounts of D-Ala in the clinical samples without severe interference from intrinsic substances in the human physiological fluids. In the volunteers having normal sleep-awake patterns, the amounts of D-Ala in the serum were high in the late evening and low in the morning. On the other hand, in the volunteers having the reversed sleep-awake patterns, the amounts of D-Ala in the serum were high in the morning and low in the nighttime. The similar circadian changes of D-Ala amounts were observed in the urine. These 24-h profiles of D-Ala are almost the same as those observed in rats and mice, suggesting that D-Ala has fundamental physiological functions related to rest-active conditions in mammals, and could also be useful as the biomarker for sleep-awake profiles.
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