Neuropeptide secretion in exercise

Plasma concentrations of atrial natriuretic peptide immunoreactivity (irANP) and brain natriuretic peptide immunoreactivity (irBNP) in elderly normal subjects (mean age 71.1, range 66-81 years, n = 10) were examined before (rest), during (peak of exercise) and after (3 min, 6 min) a treadmill exercise test (modified Bruce protocol). An attempt was also made to determine the effect of steady state exercise (30% and 50%) and posture (supine, sitting) on circulating levels of atrial natriuretic peptide and calcitonin gene-related peptide (CGRP) in man. The results suggest that exercise gives rise to increased levels of irANP and irCGRP, but not human BNP. The study also demonstrated a >40% rise in irCGRP and irANP levels at 50% steady state exercise compared with 30% steady state exercise. irCGRP was shown to decline in the upright position compared with the supine position, and irCGRP did not rise with exercise. Although ANP is normally stored in large concentration in the atria with much less in the ventricles and BNP is derived to a much greater extent from the ventricles, the differential release rate of these peptides may make BNP concentration a more sensitive indicator of left ventricular dysfunction than ANP. The observations obtained here also raise the possibility that the ANP system may not only help to eliminate intermittent overhydration, but also participate in the postural regulation of diuresis and natriuresis and perhaps even support the maintenance of excretory kidney function in the ageing subjects.