Reduced Insulin Secretion and Nocturnal Dipping of Blood Pressure Are Associated with a Disturbed Circadian Pattern of Urine Excretion in Metabolic Syndrome

Introduction: An impaired Na and water excretion rate during daytime is associated with increased cardiovascular risk factors. Recent findings suggest that disturbed circadian rhythms may play an important role in salt-sensitive hypertension and reduced beta-cell function. Methods: This study investigated clinical implications of the circadian pattern of urine excretion [evaluated as the day to night ratio of urine flow rate (D/N of V)] in 76 patients with metabolic syndrome (MS) not taking diuretics. We analyzed 24-h urinary excretion and blood pressure (BP) during separate day and night periods. In addition nondiabetic patients (n = 46 of 76) underwent an oral glucose tolerance test. Results: The D/N of V varied largely among subjects (tertile 1 = 1.95 +/- 0.40, tertile 3 = 0.67 +/- 0.14). In the patients with low D/N of V, systolic BP dipped less at night, independently of age and creatinine clearance (P < 0.01). During the first 60 min of the oral glucose tolerance test, the rise in plasma insulin and the insulinogenic index were positively correlated with the D/N of V, even after adjustment for age, waist circumference, 24-h urine volume, and BP (P < 0.001 for both), suggesting inadequate insulin secretion in poor daytime excretors. Conclusion: In patients with MS, a disturbed circadian pattern of urine excretion is associated with a reduced nocturnal dipping of systolic BP and a reduced glucose-induced insulin secretion. These results underline the clinical importance of impaired circadian rhythms in MS and prompt further studies to evaluate the potential of the D/N of V as a prognostic marker in MS patients. (J Clin Endocrinol Metab 96: E929-E933, 2011)