Rise in Plasma Noradrenaline with Age Results from an Increase in Spillover Rate

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Abstract
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 < 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 < 0.001). Plasma NA clearance was similar in young and elderly subjects. NA spillover was positively correlated with age (r = 0.58; p < 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.