Disturbed Circadian Rhythm of Urinary Albumin Excretion in Non-Dipper Type of Essential Hypertension

Abstract

Recently, we found that the circadian rhythms of natriuresis as well as of glomerular filtration rate were disturbed similar to the blood pressure in non-dipper type of essential hypertension during intake of a high-sodium diet. In this study, we examined circadian rhythms of the urinary albumin excretion rate (AER), which is recognized as a marker of glomerular capillary hydraulic pressure, in addition to those of urinary sodium excretion and blood pressure in 27 patients with essential hypertension. The patients were maintained on relatively high (10–12 g) on low (1–3 g) sodium (NaCl) diets for 1 week. On the last day of each diet, the 24-hour blood pressure was measured every 30 min noninvasively, and during the last 3 days, urine samples were collected for determination of both daytime (07:00–21.30 h) and nighttime (21.30–07.00 h) sodium and AER variations. During the high-sodium diet, nocturnal falls in urinary sodium excretion and blood pressure were observed in dippers (n = 7), while they were not observed in non-dipper (n = 20). The nocturnal decline in AER was also observed in dippers (day: 37 ×/÷ 6 µg/min vs. night: 22 ×/÷ 5 µg/min; p < 0.02), while it was not observed in non-dippers (day: 49 ×/÷ 6 µg/min vs. night: 40 ×/÷ 8 µg/min; NS). During intake of the low-sodium diet, on the other hand, a nocturnal decline in AER was observed in both types of hypertension. Sodium restriction significantly reduced only the nighttime AER in non-dippers (p < 0.01). These findings indicate that changes in dietary sodium intake modified the circadian rhythms of both blood pressure and AER in non-dippers. Renal sodium handling may contribute to determining the circadian rhythm of blood pressure, and furthermore an elevated glomerular capillary hydraulic pressure during the night may enhance the nocturnal albumin excretion in non-dippers.