Nyctohemeral Rhythm of Plasma Renin Activity and Plasma Aldosterone in Children

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Abstract
Summary: Circadian rhythms of plasma renin activity (PRA) and plasma aldosterone (PA) were studied in eight healthy children, 7 to 15 years old. Blood samples were obtained at 7:00 AM, 10:00 AM, 1: 00 PM, 4:00 PM, 5:00 PM, 8.00 PM, and midnight on day 1 and 4:00 AM and 7:00 AM on day 2. Children had normal activity during this test. Intra- and interindividual changes were noted in PRA in plasma taken in the upright position. Mean PRA values for samples taken in the upright position were maximal at 1:00 PM (7 ng/ml/hr) and minimal at 5:00 PM (4.1 ng/ml/hr). Mean PRA in the supine position was maximal at 4:00 AM on day 2 (5.6 ng/ml/hr), and its rise was statistically significant compared with the mean PRA at 7:00 AM on the same day (3.9 ng/ml/hr). Plasma aldosterone varied without any definite pattern. No correlation was found between PRA and PA and between PRA and PA and 24-hr urinary sodium excretion. Speculation: This study shows the extreme variability of plasma renin activity and plasma aldosterone values during the nyctohemeron. It is well known that the dispersion of values for plasma renin activity and plasma aldosterone is greater in children than in adults even after age correction. We therefore speculated that the reactivity to different stimuli of the renin-angiotensin-aldosterone system is increased in children. Consequently, more than one plasma sample is required to evaluate the renin-angiotensin-aldosterone system in children.

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