The relationship between age and venous plasma concentrations of noradrenaline, catecholamine metabolites, DOPA and neuropeptide Y-like immunoreactivity in normal human subjects.

Forearm venous plasma concentrations of noradrenaline (NA), catecholamine metabolites (dihydroxyphenylglycol (DHPG), dihydroxyphenylacetic acid (DOPAC], dihydroxyphenylalanine (DOPA) and neuropeptide Y-like immunoreactivity (NPY-LI) were studied in 22 men aged 20 to 81 years in the supine position and after 30 min of standing posture. Venous plasma NA, DHPG and NPY-LI increased significantly in the standing position, whereas venous plasma DOPAC and venous plasma DOPA remained unchanged. Increments in venous plasma NA and DHPG upon standing up, as well as venous plasma NA in the standing-up position, increased significantly with age. The ratio between increments in venous plasma DHPG and venous plasma NA did not change with age. Venous plasma NPY-LI and venous plasma DOPA did not change with age, whereas venous plasma DOPAC decreased significantly. Changes in venous plasma NPY-LI were negatively correlated with changes in pulse pressure. These results confirm previous studies that sympathetic activity increases with age. The unchanged ratio between increments in venous plasma DHPG and venous plasma NA suggests that intra-neuronal deamination of recaptured NA is unchanged in the elderly. The lower basal venous plasma DOPAC concentration may suggest a reduced basal intraneuronal synthesis of NA in old age.