Decreased active vasodilator sensitivity in aged skin.
Kenney, W. L., A. L. Morgan, W. B. Farquhar, E. M. Brooks, J. M.
Pierzga, and J. A. Derr.
Noll Physiological Research Center, Penn State University,
University Park, PA 16802-6900, Statistical Consulting Center, Penn
State University, University Park, PA 16802)
APStracts 3:0519H, 1996.
Older men and women respond to local and reflex-mediated heat stress
with an attenuated increase in cutaneous vascular conductance (CVC).
This study was performed to test the hypothesis that an augmented or
sustained noradrenergic vasoconstriction (VC) may play a role in this
age-related difference. Fifteen young (22+/-1 yr) and 15 older (66+/
-1 yr) men exercised at 50% VO2peak in a 36C environment. Skin
perfusion was monitored at 2 sites on the right forearm by laser
-Doppler flowmetry, one site pretreated with bretylium tosylate (BT)
to block the local release of norepinephrine and thus VC, and an
adjacent control site. Blockade of reflex VC was verified during
whole-body cooling using a water-perfused suit. CVC (=perfusion/mean
arterial pressure) at each site was reported as a percent of the
maximal CVC (%CVCmax) induced at the end of each experiment by
prolonged local heating at 42C. Neither age nor BT affected the
%CVCmax (75% - 86%) attained at high core temperatures. During the
early rise phase of CVC, the %CVCmax:_Tes curve was shifted to the
right in the older men (ET50 for young = 0.22+/-0.04 and 0.39+/
-0.04C, for older = 0.73+/-0.04 and 0.85+/-0.04C at control and BT
sites, respectively). BT had no interactive effect on this age
difference, suggesting a lack of involvement of the VC system in the
attenuated CVC response of individuals over the age of 60 yr.
Additionally, increases in skin vascular conductance were
quantitatively compared by measuring increases in total forearm
vascular conductance (FVC, restricted to the forearm skin under these
conditions). After the initial 0.2C increase in esophageal
temperature (Tes), FVC was 40-50% lower in the older men
(p<0.01) for the remainder of exercise. Decreased active
vasodilator sensitivity to increasing core temperature, coupled with
structural limitations to vasodilation, appear to limit the cutaneous
vascular response to exertional heat stress in older subjects.
Received 1 August 1996; accepted in final form 1 November 1996.
APS Manuscript Number H700-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996