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1 Noll Physiological Research Center2 Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802-6900, USA
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°C using a water-perfused suit. Cutaneous vascular conductance (CVC; LDF/mean arterial pressure) was expressed as percentage change from baseline (%
CVCbase). Solutions of yohimbine + propranolol (Y + P), bretylium tosylate (BT), and lactated Ringer solution were infused via intradermal microdialysis at each LDF site to antagonize 
- and ß-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%CVCbase, P < 0.001). Y + P attenuated VC in young subjects (–13 ± 8%CVCbase, P < 0.001 versus control) and abolished VC in older subjects (0 ± 3%CVCbase, 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.
(Received 2 April 2004;
accepted after revision 28 May 2004;
first published online 4 June 2004)
Corresponding author W. L. Kenney: The Pennsylvania State University, 119 Noll Laboratory, University Park, PA 16802, USA. Email: w7k{at}psu.edu
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