title: Altered neurotransmitter control of reflex vasoconstriction in aged human skin.
abstract: Cutaneous vasoconstriction (VC) in response to cooling is attenuated in older humans; however, mechanisms underlying this functional decline remain unclear. The present study tested the hypothesis that the contributions of noradrenaline (NA) and sympathetic cotransmitters to reflex-mediated cutaneous VC are altered with age. In 11 young (18-26 years) and 11 older (61-77 years) men and women, forearm skin blood flow was monitored at three sites using laser Doppler flowmetry (LDF) while mean skin temperature was lowered from 34 to 30.5 degrees C using a water-perfused suit. Cutaneous vascular conductance (CVC; LDF/mean arterial pressure) was expressed as percentage change from baseline (% DeltaCVC(base)). Solutions of yohimbine + propranolol (Y + P), bretylium tosylate (BT), and lactated Ringer solution were infused via intradermal microdialysis at each LDF site to antagonize alpha- and beta-adrenoceptors, block sympathetic release of NA and cotransmitters, and act as control, respectively. During cooling, VC was attenuated at the control site in older subjects compared to young subjects (-16 +/- 3 versus-34 +/- 4% DeltaCVC(base), P < 0.001). Y + P attenuated VC in young subjects (-13 +/- 8% DeltaCVC(base), P < 0.001 versus control) and abolished VC in older subjects (0 +/- 3% DeltaCVC(base), P > 0.9 versus baseline). BT completely blocked VC in both age groups. Cutaneous VC in young subjects is mediated by both NA and sympathetic cotransmitter(s); however, reflex VC in aged skin is attenuated compared to young and appears to be mediated solely by NA.
authors.affiliation: The Pennsylvania State University, 119 Noll Laboratory, University Park, PA 16802, USA.
authors.forename: Caitlin S
authors.initials: CS
authors.lastname: Thompson
authors.forename: W Larry
authors.initials: WL
authors.lastname: Kenney
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D012867:Skin / Q000098:blood supply* / Q000294:innervation; D013564:Sympathetic Nervous System / Q000502:physiology; D014661:Vasoconstriction / Q000502:physiology*
chemical_list: D009638:Norepinephrine