AGING AND ALPHA-ADRENERGIC CONTROL OF MUSCLE BLOOD FLOW

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Muscle sympathetic nerve activity (MSNA) plays an important role in the regulation of basal limb vascular tone, as well as regulating limb blood flow during exercise. Resting MSNA increases markedly with age in humans, and recent studies suggest that the vasoconstrictor responses to acute and chronic elevations in MSNA are blunted in older adult humans. Additionally, data regarding sympathetic control of blood flow to contracting skeletal muscle in older adults is lacking. The proposed experiments will determine whether I) the blunted vasoconstriction with age is due to reduced postganglionic alpha-adrenergic receptor responsiveness; 2) the specific alpha-adrenergic receptor subtype contribution to basal and stimulated vascular tone is altered with age; and 3) older adults demonstrate more robust sympathetic vasoconstriction in active skeletal muscle compared with young adults. The strength of the proposed experimental design is that we will target the specific alpha- receptor subtypes before and after abolishing basal sympathetic outflow to the forearm with local anesthetics given at the stellate ganglion. These experiments will provide important new information about sympathetic control of blood flow to resting and contracting skeletal muscle in aging humans.