Circadian rhythm and postural change in natriuresis in non-dipper type of essential hypertension

Recently we found that, in non-dipper type of essential hypertensive patients who showed the lack of nocturnal fall in blood pressure, circadian rhythm of urinary sodium excretion rate was disturbed. In the present study we examined whether postural change in natriuresis is also disturbed in non-dippers. Sixteen inpatients with essential hypertension were maintained on a relatively high sodium diet containing 10 to 12 g of NaCl per day for 8 days. On the 7th day of the study period, 24-h ambulatory blood pressures were measured, and 5-7th days urinary samples were collected for both daytime and night-time. On the last day of the study period, patients stood for 2 h and then lay down for 2 h. Urinary volume and excretion rates of creatinine and sodium were measured every hour in both positions. Night-time urinary sodium excretion rate was significantly higher in non-dippers (n = 9) than that in dippers (n = 7). Night/day ratio of mean arterial pressure had a positive relationship with night/day ratio of urinary sodium excretion rate. In non-dippers, but not in dippers, the mean value of U(Na)V during upright position was significantly lower than that during supine position. There was a significantly negative relationship between upright/supine ratio of U(Na)V and night/day ratio of MAP or night/day ratio of U(Na)V. In patients with non-dipper type of essential hypertension, both natriuresis patterns, circadian rhythm and postural change, were disturbed.