Rise in plasma noradrenaline with age results from an increase in spillover rate.

Venous plasma noradrenaline (NA) kinetics, determined using steady-state intravenous infusions of subpressor doses of [3H] NA, were measured in 8 young, 13 middle-aged and 8 elderly subjects. Plasma NA concentrations were 0.71 nmol/l (0.25-0.98) in the young, 1.90 nmol/l (0.98-3.65) in the middle-aged and 3.03 nmol/l (1.15-3.85) in the elderly (young vs. elderly, p less than 0.001). NA spillover rates were 2.07 nmol/l/m2 (1.05-4.91) in the young, 3.91 nmol/l/m2 (1.62-9.44) in the middle-aged and 7.57 nmol/l/m2 (4.38-24.0) in the elderly (young vs. elderly, p less than 0.001). Plasma NA clearance was similar in young and elderly subjects. NA spillover was positively correlated with age (r = 0.58; p less than 0.01) and was not independently related to blood pressure. The rise in plasma NA with age results from an increase in spillover rate rather than any alteration in clearance.