Impaired nocturnal Melatonin secretion in non-dipper hypertensive patients

Melatonin plays a role in the biologic regulation of circadian rhythms, including sleep. Melatonin has also been shown to modulate vascular smooth muscle tone and to induce hemodynamic effects in humans. To evaluate whether melatonin plays a role in the circadian rhythm of blood pressure in hypertensive patients. Sixteen elderly patients with essential hypertension were evaluated. Patients were defined as either dippers (DIP, n = 8) or non-dippers (NDIP, n = 8) according to the nocturnal change in the mean arterial pressure (MAP). 6-Sulfatoxymelatonin (6-SMT), the main melatonin metabolite, was determined by enzyme-linked immunosorbent assay (ELISA) in two separate urine collections, one in the daytime and one during the night. Both groups of DIP and NDIP hypertensives were comparable in regard to age and sex. During the night, the mean arterial pressure decreased by 10.3 +/- 2.2% in the DIP and increased by 7.5 +/- 1.7% in the NDIP group (p < 0.01). Daily 6-SMT was comparable in DIP (3.28 +/- 0.87 microg/12 h) and NDIP (2.31 +/- 0.68 microg/12 h) (p = 0.39). However, while the DIP presented the physiological nocturnal increase in urinary 6-SMT (mean 8.19 +/- 1.68 microg/ 12 h), this surge of melatonin production was missing in NDIP in whom nocturnal urinary 6-SMT concentrations were not significantly different from daily levels (mean 2.56 +/- 0.79 microg/12 h). The nocturnal change in urinary 6-SMT excretion was positively correlated to the nocturnal change in MAP (R = 0.54; p = 0.031). NDIP hypertensive patients differ from DIP hypertensives by having an impaired nocturnal melatonin secretion. Thus, melatonin may play a role in the circadian rhythm of blood pressure in hypertensive patients.