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Regulation of skeletal muscle blood flow in the elderly: role of alpha‐1 adrenergic receptor sensitivity
Author(s) -
Wray David Walter,
Nishiyama Steven K.,
Harris Ryan A.,
Richardson Russell S.
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.967.8
Subject(s) - vasoconstriction , medicine , blood flow , phenylephrine , heart rate , blood pressure , femoral artery , endocrinology , cardiology
In nine young (25 ± 1 yrs) and six older (72 ± 2 yrs) healthy volunteers, we evaluated changes in leg blood flow (ultrasound Doppler) during blood flow‐adjusted, intra‐arterial infusion of phenylephrine (PE, a selective alpha‐1 adrenergic agonist) at rest and during knee‐extensor exercise. Heart rate, arterial blood pressure, femoral artery diameter, and blood velocity were measured in all subjects at rest and exercise at 20, 40, and 60% of maximal work rate (WR max ). In a subset of subjects ( n = 10), leg O 2 consumption (VO 2 ) and lactate efflux were also evaluated. At rest, PE reduced blood flow to a lesser degree in older (−37 ± 3%) compared to young (−54 ± 4%) subjects. During exercise, older subjects maintained a greater vasoconstrictor response to PE at 40% WR max (−14 ± 3%, older; −7 ± 2%, young) and 60% WR max (−11 ± 3%, older; −4 ± 3%, young), which may be attributed to lower absolute work rates in the older group. At a similar absolute work rate and leg VO 2 , vasoconstriction to PE was not different between groups (−14 ± 3%; older; −17 ± 5%, young). In both groups, blunting of PE‐mediated vasoconstriction was highly correlated with leg VO 2 but not leg lactate efflux. Together, these data indicate that alpha‐1 adrenergic receptors become less sensitive during knee extensor exercise as a consequence of absolute work and the associated level of oxidative metabolism, with no effect of age per se .