Augmented leg vasoconstriction in dynamically exercising older men during acute sympathetic stimulation

Vasoconstrictor responsiveness to acute sympathetic stimulation declines with advancing age in resting skeletal muscle. The purpose of the present study was to determine if age-related reductions in sympathetic vasoconstrictor responsiveness also occur in exercising skeletal muscle. Thirteen younger (20-30 years) and seven older (62-74 years) healthy non-endurance-trained men performed cycle ergometer exercise at ∼60 % of peak oxygen uptake while leg blood flow (femoral vein thermodilution), mean arterial blood pressure (radial artery catheter), and plasma adrenaline and noradrenaline concentrations were measured. After steady state was reached (i.e. ∼4 min), acute sympathetic stimulation was achieved by immersing a hand in ice water for 2-4 min (cold pressor test, CPT). CPT tended to cause a larger increase in mean arterial blood pressure in older men (older (O): 16 ± 3 mmHg; younger (Y): 10 ± 2 mmHg) during exercise, but increases in arterial noradrenaline were similar (O: 2.56 ± 0.96 nM; Y: 1.98 ± 0.40 nM). However, the older men demonstrated a larger percentage reduction in exercising leg vascular conductance (leg blood flow/mean arterial pressure) during CPT compared to younger men (O:-13.6 ± 3.1 %; Y:-1.5 ± 4.3 %; P=0.04). Leg blood flow tended to increase in the younger men, but not in the older men (P=0.10). These results suggest, in contrast to what has been observed in resting skeletal muscle, that vasoconstrictor responsiveness to sympathetic stimulation is not reduced, but may be augmented in exercising muscle of healthy older humans. This could reflect a reduced ability of local substances (e.g. nitric oxide) to impair vasoconstriction in response to sympathetic stimulation during exercise in older humans.