Comparison of circadian rhythms of the renin-angiotensin-aldosterone system and electrolytes in clinically healthy young women in Fukuoka (Japan) and Minnesota (USA)

Abstract

Circadian rhythms of the renin-angiotensin\x=req-\ aldosterone (R-A-A) system and electrolytes were evaluated in young healthy Fukuokan (Japan) and Minnesotan (USA) women. A similar protocol was used and each group remained on its usual diet. Blood was taken for 24 h at 4 h intervals from 8 a.m. during which time urine samples were also collected. The determinations in both groups were made in a laboratory in Japan. Plasma renin activity, plasma aldosterone concentration and aldosterone excretion rate showed similar circadian rhythms in both groups. However, those values at each sampling time and each span were always significantly higher in the Americans while the urinary Na and Cl excretions and blood pressure were higher in Japanese. The significant differences in the R-A-A system and blood pressure levels between these two groups may be due to the large amount of salt consumed by the Japanese.It has recently been reported that the Yanomamo Indians, a 'no-salt' culture, showed strikingly high levels of the renin-angiotensin-aldosterone (R-A-A) system (Oliver et al. 1975). The differing dietary habits of Japanese and North Americans may lead to differences in the R-A-A system as daily con¬ sumption of salt per person in Japan is habitually higher than in North America (Dahl 1972).A collaborative study between the Universities of Kyushu (Fukuoka, Japan) and Minnesota (Minnea¬ polis, USA) has already demonstrated remarkable differences in the rhythm-adjusted mean (mesor) and the circadian rhythm of plasma prolactin ) and plasma renin activity, analy¬ zed by means of the cosinor method ). In the present study, an identical proto¬ col was used for young adult Fukuokan and Minnesotan women and all chemical determinations were performed in the same laboratory. Differences in the means and the circadian rhythms of the R-A-A system and electrolytes in urine between the two groups, studied in the same season and in a com¬ parable fashion, are reported herein. Materials and Methods SubjectsTwenty young Japanese women between 20 and 21 years of age and 16 young American women, Caucasians of mixed ethnic origin, between 18 and 24 years of age were accepted for the study after a complete history and physical examination, which showed evidence of neither endocrine nor circulatory disorders and no active disea¬ ses of any nature. Subjects from Minnesota were signifi¬ cantly taller and heavier than those from Fukuoka, but did not differ in body mass index. The distribution of menstrual stage of the two groups did not differ.

Second morning urine method is superior to the casual urine method for estimating daily salt intake in patients with hypertension

“…With all three levels of salt intake tested, the intake estimated by the CU equation was lower with morning urine samples than with afternoon samples (Figure 2). This was probably related to the circadian rhythm of urinary sodium excretion, [25][26][27][28] which results in lower excretion during the morning than during the afternoon. As the creatinine excretion rate is almost constant throughout 24 h, 29 the urinary sodium/ creatinine ratio reflects the circadian rhythm of sodium excretion and the estimated salt intake is lower when a morning urine sample is employed than with an afternoon urine sample.…”

The influence of posture on the estimation of daily salt intake by the second morning urine method

“…34 However, this method can actually be used in patients receiving antihypertensive therapy because there were no differences between the SMU and 24-h collection methods for any class of antihypertensive (Figure 4). These findings agreed with our previous results.…”

Effectiveness of a Spot Urine Method in Evaluating Daily Salt Intake in Hypertensive Patients Taking Oral Antihypertensive Drugs

“…The usefulness of the SUM has been confirmed in population studies (8)(9)(10)(11) and in hypertensive patients who were taking no medicine (12,13). While calcium channel blockers (14), angiotensin-converting enzyme inhibitors, and diuretics (15) have a natriuretic action, α-blockers (16) have an anti-natriuretic action, and these differing effects presumably could affect daily salt intake estimated by SUM in med-icated patients by altering the circadian rhythm of sodium secretion (17). Therefore, we here investigated whether or not the SUM is applicable to patients taking oral antihypertensive medications on a regular basis by comparing results with those in hypertensive patients who took no medicine.…”