DIURNAL VARIATION OF THE ALDOSTERONE-TO-RENIN RATIO PEAKS IN THE MORNING IN NORMOTENSIVE AND HYPERTENSIVE INDIVIDUALS

Objective: The purpose of the study is to examine the 24-hour variations of plasma aldosterone concentration, plasma renin activity and the aldosterone-to-renin ratio.Design and method: We analyzed data from 41 normotensive and hypertensive individuals who were admitted in a metabolic ward for the experiment. Testing conditions were standardized, including controlled sodium intake, calorie intake, room temperature, and light and sound exposure. Medications were discontinued two weeks prior to the investigation. A verified sleep-wake cycle was maintained with nocturnal sleep duration of 7-8 hours. Supine measurements of plasma aldosterone concentration, plasma renin activity and the aldosterone-to-renin ratio were obtained at regular intervals without disturbing the participants during sleep. Hormonal measurements were sequentially divided into four 6-hour periods, 00:00-06:00, 07:00-12:00, 13:00-16:00 and 18:00-24:00 hr. Results: Our study demonstrates significant variations in plasma aldosterone concentration, with a peak level of 474.5 pmol/L during the 06:00-12:00 period and trough level of 267.3 during the 18:00-24:00 period. Plasma renin activity also changed significantly across the four time periods, peaking to 20.4 mIU/L between 01:00 and 06:00 hr, with its lowest level of 15.3 mIU/L between 18:00-24:00 hr. Mean values of plasma aldosterone concentration and active plasma renin concentration correlated positively and significantly with the amplitude of their 24-hour change. Finally, the aldosterone-to-renin ratio exhibited significant variations cresting at 27.3 during the 06:00-12:00 period and the trough of 16.8 during 12:00-18:00 period. Among various confounding factors, mean arterial pressure, heart rate, age and BMI were significant influences of the aldosterone-to-renin ratio. Conclusions: We conclude that the aldosterone-renin-ratio changes significantly over a 24-hour period, reinforcing the important but understudied role that diurnal effects play in interpreting the aldosterone-to-renin ratio.