| Autor: |
Simpson LL; Department of Sport Science, Division of Performance Physiology and Prevention, Universität Innsbruck, Innsbruck, Austria., Hansen AB; Department of Sport Science, Division of Performance Physiology and Prevention, Universität Innsbruck, Innsbruck, Austria., Moralez G; Department of Applied Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas, United States., Amin SB; Department of Sport Science, Division of Performance Physiology and Prevention, Universität Innsbruck, Innsbruck, Austria., Hofstaetter F; Department of Sport Science, Division of Performance Physiology and Prevention, Universität Innsbruck, Innsbruck, Austria., Gasho C; Department of Medicine, Division of Pulmonary and Critical Care, Loma Linda University, Loma Linda, California, United States., Stembridge M; Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, Wales, United Kingdom., Dawkins TG; Centre of Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada., Tymko MM; Centre of Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada.; Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada.; Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada., Ainslie PN; Centre of Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada., Lawley JS; Department of Sport Science, Division of Performance Physiology and Prevention, Universität Innsbruck, Innsbruck, Austria.; Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy., Hearon CM Jr; Department of Applied Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas, United States.; Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Dallas, Dallas, Texas, United States. |
| Abstrakt: |
Sympathetic transduction is reduced following chronic high-altitude (HA) exposure; however, vascular α-adrenergic signaling, the primary mechanism mediating sympathetic vasoconstriction at sea level (SL), has not been examined at HA. In nine male lowlanders, we measured forearm blood flow (Doppler ultrasound) and calculated changes in vascular conductance (ΔFVC) during 1 ) incremental intra-arterial infusion of phenylephrine to assess α 1 -adrenergic receptor responsiveness and 2 ) combined intra-arterial infusion of β-adrenergic and α-adrenergic antagonists propranolol and phentolamine (α-β-blockade) to assess adrenergic vascular restraint at rest and during exercise-induced sympathoexcitation (cycling; 60% peak power). Experiments were performed near SL (344 m) and after 3 wk at HA (4,383 m). HA abolished the vasoconstrictor response to low-dose phenylephrine (ΔFVC: SL: -34 ± 15%, vs. HA; + 3 ± 18%; P < 0.0001) and markedly attenuated the response to medium (ΔFVC: SL: -45 ± 18% vs. HA: -28 ± 11%; P = 0.009) and high (ΔFVC: SL: -47 ± 20%, vs. HA: -35 ± 20%; P = 0.041) doses. Blockade of β-adrenergic receptors alone had no effect on resting FVC ( P = 0.500) and combined α-β-blockade induced a similar vasodilatory response at SL and HA ( P = 0.580). Forearm vasoconstriction during cycling was not different at SL and HA ( P = 0.999). Interestingly, cycling-induced forearm vasoconstriction was attenuated by α-β-blockade at SL (ΔFVC: Control: -27 ± 128 vs. α-β-blockade: +19 ± 23%; P = 0.0004), but unaffected at HA (ΔFVC: Control: -20 ± 22 vs. α-β-blockade: -23 ± 11%; P = 0.999). Our results indicate that in healthy males, altitude acclimatization attenuates α 1 -adrenergic receptor responsiveness; however, resting α-adrenergic restraint remains intact, due to concurrent resting sympathoexcitation. Furthermore, forearm vasoconstrictor responses to cycling are preserved, although the contribution of adrenergic receptors is diminished, indicating a reliance on alternative vasoconstrictor mechanisms. |
