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  • Title: Role of catecholamines and beta-receptors in ventilatory response during hypoxic exercise.
    Author: Warner MM, Mitchell GS.
    Journal: Respir Physiol; 1991 Jul; 85(1):41-53. PubMed ID: 1658899.
    Abstract:
    The ventilatory response to moderate exercise in hypoxia is potentiated in goats, decreasing PaCO2 more than in normoxic exercise. We investigated the hypothesis that this potentiation results from a ventilatory stimulus provided by increased levels of circulating catecholamines (norepinephrine and/or epinephrine), acting via beta-receptors. Plasma norepinephrine [NE] and epinephrine [E] concentrations, arterial blood gases and ventilation were measured in normoxia and hypoxia (PaO2 = 34-38 Torr) at rest and during moderate exercise (5.6 kph; 5% grade) in seven female goats. PaCO2 decreased from rest to exercise in normoxia (2.9 +/- 0.7 Torr; P less than 0.01), and decreased significantly more from rest during hypoxic exercise (6.4 +/- 0.6 Torr; P less than 0.01). [NE] increased in both normoxic (1.1 +/- 0.4 ng/ml; P less than 0.05) and hypoxic exercise (2.5 +/- 0.5 ng/ml; P less than 0.01); the [NE] increase in hypoxia was significantly greater (P less than 0.01). [E] increased in normoxic (0.3 +/- 0.1 ng/ml; P less than 0.05) but not hypoxic exercise (0.6 +/- 0.5 ng/ml; P greater than 0.2). Experiments were repeated following administration of the beta-adrenergic receptor blocker, propranolol (2 mg/kg, i.v.). After beta-blockade, PaCO2 decreases from rest to exercise in normoxia (3.2 +/- 0.7 Torr; P less than 0.01) and hypoxia (8.1 +/- 0.7 Torr; P less than 0.001) were not significantly different from control. The data indicate that beta-adrenergic receptor stimulation is not necessary for a greater decrease in PaCO2 during hypoxic versus normoxic exercise. The greater rise in [NE] suggests a possible role in ventilatory control during hypoxic exercise, perhaps via alpha-adrenergic receptors. However, recent evidence suggests that NE is inhibitory in goats, and that NE is unlikely to mediate extra ventilatory stimulation during hypoxic exercise.
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