Circadian rhythm of urinary potassium excretion in patients with CKD

Aims: We previously reported in patients with chronic kidney disease (CKD) that the circadian rhythms of blood pressure (BP) and urinary sodium excretion were both impaired into non-dipper pattern as renal function deteriorated. However, the circadian rhythm of urinary potassium excretion has not been studied in relation to renal dysfunction. Methods: BP and urinary excretion rates of sodium (UNaV) and potassium (UKV) were evaluated for day-time and night-time to estimate their circadian rhythms in 83 subjects with CKD. Results: As renal function deteriorated, night/day ratios of UNaV and UKV were both increased. Night/day ratio of UKV was positively correlated with night/day ratio of UNaV (r = 0.60, p < 0.0001). Multiple regression analysis (R-2 = 0.37, p < 0.0001) revealed that night/day ratio of UKV was determined independently by the night/day ratio of UNaV (r = -0.55, p < 0.0001), rather than renal function or night/day ratio of BP. Conclusions: Circadian rhythm of natriuresis was regulated by renal function and night/day ratio of BP. On the other hand, the circadian rhythm of urinary potassium excretion was primarily determined by neither renal function nor BP, but was correlated with that of urinary sodium excretion.