Journal of Applied Physiology, Vol 67, Issue 6 2438-2446, Copyright © 1989 by American Physiological Society
Ventilatory control during exercise with peripheral chemoreceptor stimulation: hypoxia vs. domperidone
S. L. Schaefer and G. S. Mitchell
Department of Comparative Biosciences, University of Wisconsin, Madison 53706.
Hypoxia potentiates the ventilatory response to exercise, eliciting a
greater decrease in arterial PCO2 (PaCO2) from rest to exercise than in
normoxia. The mechanism of this hypoxia-exercise interaction requires
intact carotid chemoreceptors. To determine whether carotid chemoreceptor
stimulation alone is sufficient to elicit the mechanism without whole body
hypoxia, ventilatory responses to treadmill exercise were compared in goats
during hyperoxic control conditions, moderate hypoxia (PaO2 = 38-44 Torr),
and peripheral chemoreceptor stimulation with the peripheral dopamine
D2-receptor antagonist, domperidone (Dom; 0.5 mg/kg iv). Measurements with
Dom were made in both hyperoxia (Dom) and hypoxia (Dom/hypoxia). Finally,
ventilatory responses to inspired CO2 at rest were compared in each
experimental condition because enhanced CO2 chemoreception might be
expected to blunt the PaCO2 decrease during exercise. At rest, PaCO2
decreased from control with Dom (-5.0 +/- 0.9 Torr), hypoxia (-4.1 +/- 0.5
Torr), and Dom/hypoxia (-11.1 +/- 1.2 Torr). The PaCO2 decrease from rest
to exercise was not significantly different between control (-1.7 +/- 0.6
Torr) and Dom (-1.4 +/- 0.8 Torr) but was significantly greater in hypoxia
(-4.3 +/- 0.7 Torr) and Dom/hypoxia (-3.5 +/- 0.9 Torr). The slope of the
ventilation vs. CO2 production relationship in exercise increased with Dom
(16%), hypoxia (18%), and Dom/hypoxia (68%). Ventilatory responses to
inspired CO2 at rest increased from control to Dom (236%) and Dom/hypoxia
(295%) and increased in four of five goats in hypoxia (mean 317%).(ABSTRACT
TRUNCATED AT 250 WORDS)
