Circadian rhythm of calcitonin gene-related peptide in uncomplicated essential hypertension

OBJECTIVE: To assess the existence of an altered circulating pattern of calcitonin gene-related peptide (CGRP) in hypertension. DESIGN: The 24 h variation in plasma CGRP was measured and compared in 10 patients affected by uncomplicated essential hypertension and in nine age- and sex-matched healthy volunteers. The diurnal variations in blood pressure, atrial natriuretic peptide (ANP), plasma renin activity (PRA), plasma aldosterone and plasma cortisol were also assessed. METHODS: Recumbency studies were performed under standardized, drug-free conditions beginning at 0800 h. Venous samples were drawn every 4 h for 24 h and hormone levels were assessed with specific radioimmunoassays. The blood pressure was measured every 15 min with a SpaceLabs 90207 monitor. RESULTS: The mean 24-h plasma CGRP concentrations were significantly lower in the hypertensive group than in the control group. In both groups a circadian rhythm was present with the same pattern, but at a lower level in hypertension. A temporal sequence starting with the nocturnal rise in plasma CGRP concentrations and progressing with the elevations of ANP, PRA, and plasma aldosterone and cortisol was apparent in both groups. The nocturnal rise in the CGRP and ANP concentrations coincided with the blood pressure and the heart rate falls. CONCLUSIONS: Our data show that CGRP is lower than normal but maintains its circadian variability and its relationship with the diurnal variations in blood pressure and other hormones known to be active on the cardiovascular system.