LAUSR

The age-related increase in α-adrenergic tone may contribute to decreased leg vascular conductance (LVC) both at rest and during exercise in the old. However, the effect on passive leg movement (PLM)-induced LVC, a measure of vascular function, which is markedly attenuated in this population, is unknown. Thus, in 8 young (25±5y) and 7 old (65±7y) subjects, this investigation examined the impact of systemic β-adrenergic blockade (propanalol, PROP) alone, and PROP combined with either α1-adrenergic stimulation (phenylephrine, PE) or α-adrenergic inhibition (phentolamine, PHEN), on PLM-induced vasodilation. LVC, calculated from femoral artery blood flow and pressure, was determined and PLM-induced delta peak (LVC∆peak) and total vasodilation (LVCAUC, area under curve) documented. PROP decreased LVC∆peak (PROP: 4.8±1.8, Saline: 7.7±2.7ml/mmHg, P<0.001) and LVCAUC (PROP: 1.1±0.7, Saline: 2.4±1.6ml/mmHg, P=0.002) in the young, but not the old (LVC∆peak, P=0.931; LVC AUC, P=0.999). PE reduced baseline LVC (PE: 1.6±0.4, PROP: 2.3±0.4 ml/min/mmHg, P<0.01), LVC∆peak (PE: 3.2±1.3, PROP: 4.8±1.8ml/min/mmHg, P=0.004) and LVCAUC(PE: 0.5±0.4, PROP: 1.1±0.7ml/mmHg, P=0.011) in the young, but not the old (baseline LVC, P=0.199; LVC∆peak, P=0.904; LVCAUC, P=0.823). PHEN increased LVC at rest and throughout PLM in both groups (drug effect: P<0.05), however LVC∆peak was only improved in the young (PHEN: 6.4±3.1, PROP: 4.4±1.5ml/min/mmHg, P=0.004), and not the old (P=0.904). Furthermore, the magnitude of α-adrenergic modulation (PHEN - PE) of LVC∆peak was greater in the young compared to the old (Young: 3.35±2.32, Old: 0.40±1.59ml/min/mmHg, P=0.019). Therefore, elevated α-adrenergic tone does not appear to contribute to the attenuated vascular function with age identified by PLM.