title: Role of catecholamines and beta-receptors in ventilatory response during hypoxic exercise.
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.
authors.affiliation: Department of Comparative Biosciences, University of Wisconsin, Madison 53706.
authors.forename: M M
authors.initials: MM
authors.lastname: Warner
authors.forename: G S
authors.initials: GS
authors.lastname: Mitchell
mesh_terms: D000818:Animals; D002395:Catecholamines / Q000097:blood*; D004837:Epinephrine / Q000097:blood; D005260:Female; D006041:Goats; D000860:Hypoxia / Q000503:physiopathology; D009638:Norepinephrine / Q000097:blood; D005082:Physical Exertion / Q000502:physiology*; D011433:Propranolol / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology; D012119:Respiration / Q000502:physiology*
chemical_list: D002395:Catecholamines; D011943:Receptors, Adrenergic, beta; D011433:Propranolol; D009638:Norepinephrine; D004837:Epinephrine