Diurnal variation in cutaneous vasodilator and vasoconstrictor systems during heat stress

Ken Aoki, Dan P. Stephens, John M. Johnson

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


It is not clear whether the diurnal variation in the cutaneous circulatory response to heat stress is via the noradrenergic vasoconstrictor system or the nonadrenergic active vasodilator system. We conducted whole body heating experiments in eight male subjects at 0630 (AM) and 1630 (PM). Skin blood flow was monitored by laser-Doppler flowmetry at control sites and at sites pretreated with bretylium (BT) to block noradrenergic vasoconstriction. Noninvasive blood pressure was used to calculate cutaneous vascular conductance. The sublingual temperature (Tor) threshold for cutaneous vasodilation was significantly higher in PM at control and at BT-treated sites (both P < 0.01), suggesting the diurnal shift in threshold depends on the active vasodilator system. The slope of cutaneous vascular conductance as a percentage of its maximum with respect to Tor was significantly lower in AM at control sites only. Also, in the AM, the slope at control sites was significantly lower than that at BT-treated sites (P < 0.05), suggesting that the diurnal change in the sensitivity of cutaneous vasodilation depends on vasoconstrictor system function. Overall, the diurnal variation in the reflex control of skin blood flow during heat stress involves both vasoconstrictor and active vasodilator systems.

Original languageEnglish (US)
Pages (from-to)R591-R595
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number2 50-2
StatePublished - 2001
Externally publishedYes


  • Bretylium
  • Circadian rhythm
  • Human
  • Laser-Doppler flowmetry
  • Skin blood flow
  • Sweating
  • Thermoregulation
  • Vasoconstriction
  • Vasodilation

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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