Calcitonin Gene-Related Peptide: 24-Hour Profile and Responses to Volume Contraction and Expansion in Normal Men

Plasma immunoreactive calcitonin-gene related peptide (CGRP) concentrations were measured in 10 normal male subjects, aged 23–34 yr, who were studied under 3 separate conditions at intervals of at least 1 week. In phase 1, plasma CGRP concentrations were measured hourly for 24 h during normal activity; in phase 2, the CGRP response to diuretic-induced volume depletion and upright posture was measured over 3 h; in phase 3, the CGRP response to volume loading and supine posture was measured over 4 h. During phase 1, the mean 24-h plasma CGRP concentration averaged 30 ± 16 pmol/L; hourly CGRP concentrations ranged from 25–37 pmol/L over 24 h and oscillated from 16% below to 27% above the mean 24-h CGRP value, changes that were highly significant (P = 0.005). The peaks were at 0600 and 0700 h, while the nadirs were at 1200 and 2000 h. No significant difference was found between fasting CGRP at 0800 h and levels taken 1, 2, and 3 h postprandially (P = 0.68). During phase 2 (volume depletion and upright) mean p...