Effect of systemic yohimbine on the control of skin blood flow during local heating and dynamic exercise

W. L. Kenney, D. H. Zappe, C. G. Tankersley, J. A. Derr

Research output: Contribution to journalArticle

Abstract

We previously demonstrated that systemic α1-adrenergic blockade (prazosin) does not alter control of nonacral human skin blood flow (SkBF) during prolonged exercise. The purpose of this investigation was to examine the effects of systemic α2-adrenergic blockade on, and thus the potential contribution of α2-adrenergic vasoconstriction (VC) to, control of SkBF during graded local heating and dynamic leg exercise. Five healthy men (aged 24-30 yr) were tested after 36 h of oral yohimbine (Y; a selective α2- antagonist) treatment, or no drug [control (C)]. The dosage of Y used caused sympathetic activation, as demonstrated by significant increases in resting heart rate (Δ = 13 beats/min; P <0.05) and mean arterial pressure (MAP, Δ = 11 mmHg; P <0.05). Laser Doppler flowmetry was utilized to monitor changes in forearm cutaneous vascular conductance (CVC) during graded local heating of the forearm. During stepwise local heating of the forearm at sustained (20 min) local temperatures (T(local)) of 34-42°C, the CVC-T(local) response curve was shifted leftward by Y [half-maximum effective dose = 39.6 ± 0.2 vs. 40.8 ± 0.2°C; P <0.05). On a different day, the subjects performed 45 min of semi-upright dynamic leg exercise (at 48 ± 1% maximal oxygen consumption) in a warm (36°C) environment during which forearm blood flow (FBF; venous occlusion plethysmography) was measured and forearm vascular conductance (FVC; FBF/MAP) was calculated. From the initiation of exercise, FVC increased with a constant steep slope with Y [ΔFVC/initial 0.3°C change in esophageal temperature (ΔT(es)) = 7.2 ± 1.8 U) but showed a slower initial rate of increase over the first few minutes in the control tests (3.4 ± 0.6 U; P <0.05), resulting in a more sigmoidal-shaped curve. There were no further drug effects on FVC after this initial phase as core (esophageal) temperature (T(es)) increased further and FVC rose rapidly in both conditions. Likewise, there was no drug effect on the attenuated rise in FVC at higher T(es) levels. These results suggest that local warming reduces, but does not abolish, α2-adrenergic vasoconstriction (VC) and that α2- receptors mediate the relative VC of forearm skin during the sympathetic activation accompanying the first few minutes of exercise. However, this VC is overridden by active vasodilation as T(es) increases further. These results also confirm the idea that the functional limit to increasing SkBF during prolonged exercise is due to an alteration in active vasodilation rather than an imposition of adrenergic VC or increased vasoconstrictor activity.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume266
Issue number2 35-2
StatePublished - 1994
Externally publishedYes

Fingerprint

yohimbine
Yohimbine
vasoconstriction
Forearm
skin (animal)
Heating
blood flow
Vasoconstriction
exercise
Adrenergic Agents
Exercise
heat
Skin
blood vessels
Blood Vessels
vasodilation
Vasodilation
drugs
Temperature
Leg

Keywords

  • active vasodilation
  • adrenergic receptors
  • alpha-receptors
  • cutaneous blood flow
  • forearm blood flow
  • heat stress
  • hyperthermia
  • vasoconstriction

ASJC Scopus subject areas

  • Physiology
  • Agricultural and Biological Sciences(all)

Cite this

Effect of systemic yohimbine on the control of skin blood flow during local heating and dynamic exercise. / Kenney, W. L.; Zappe, D. H.; Tankersley, C. G.; Derr, J. A.

In: American Journal of Physiology - Heart and Circulatory Physiology, Vol. 266, No. 2 35-2, 1994.

Research output: Contribution to journalArticle

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AU - Derr, J. A.

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KW - heat stress

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