Effects of Aging on Whole-Leg α-Adrenergic Vasoconstrictor Responsiveness in Healthy Men.

Muscle sympathetic vasoconstrictor nerve activity increases with advancing age, but does not result in elevated forearm vasoconstrictor tone due to a selective reduction in α1-adrenergic receptor responsiveness. In contrast, the leg circulation of older adults is under greater tonic sympathetic vasoconstriction, but it is unclear whether leg α-receptor responsiveness is altered with age. We tested the hypothesis that α-adrenergic receptor responsiveness is not reduced in the leg circulation with age. In 12 young (24±1 yrs) and 7 healthy older men (62±2 yrs), we measured femoral blood flow (FBF; Doppler ultrasound) and calculated the vascular conductance (FVC) responses to alpha-adrenergic receptor stimulation via intra-femoral artery infusions of tyramine (evokes endogenous NE release), phenylephrine α1-agonist), and dexmedetomidine (α2-agonist) during local blockade of β-adrenergic receptors. At rest, femoral blood flow and vascular conductance were ∼30% lower in older compared with young men. Maximal vasoconstrictor responses (%ΔFVC) to tyramine (-30±3 vs -41±3%), phenylephrine (-25±4 vs -45±5%), and dexmedetomidine (-22±4 vs -44±3%) were significantly reduced in older compared with young men (all P<0.05). We conclude that aging is associated with impaired leg α-adrenergic receptor responsiveness at rest, and that this involves both α1- and α2-adrenergic receptors. [ABSTRACT FROM AUTHOR]