1973. Thc role of the aortic body chemoreceptors in the cardiac and respiratory responses to acute hypoxia in the anesthetized dog. Can. J. Physiol. Pharmacol. 51, 249-259.The participation of the aortic chen~oreceptors in the reflex cardiac responses to acute hypoxia is suggested only by the indirect evidence of pharmacological stimulation of these receptors. In order to assess their role more directly, the response to a 15 min period of hypoxia was determined aftersurgical denemation of the aortic chemoreceptors (A.D.), and compared with the response of shamoperated (S.O.) dogs, anesthetized with morphine-pentobarbital. In the control period, while breathing room air, the cardiovascular and respiratory parameters measured in the A.D. animals were not different from those of the S.O. dogs. Hypoxia (partial pressure of oxygen approximately 30 mm Hg) in the S.O. dogs was associated with a statistically significant rise in the heart rate (4 71 7 min-1, mean & S.E.M.) and of the cardiac output (4-25 -t 10 ml kg-1 min-1). In the A.D. animals, the significantly smaller increment in heart rate (-t29 + 6 min-1) was associated with a fall of the cardiac output (-16 1 12 ml kg-1 min-1). The hypaxia-induced changes in heart rate and cardiac output in the S.Q. animals were different ( p -. 0.05) from those in the A.D. group. The minute volume of ventilation was significantly augmented in both groups, and to a comparable extent. These findings indicate that the aortic chemoreceptors play a significant role in the cardiac response to hypoxia, but they do not affect, to a significant extent, the respiratory response. BIRO, G. P., HATCHER, J. D., et JENNPNGS, D. B. 1973. The role of the aortic body chemoreceptors in the cardiac and respiratory responses to acute hypoxia in the anesthetized dog. Can. J. Physiol. Pharmacol. 51, 249-259. La participation des ch6mor&cepteurs dans la reponse cardiaque d'origine reflexe a la suite d'une hypoxie aigue n'a reCu qu'une demonstration indirecte par la stimulation pharmacologique de ces recepteurs. Chez le chien anesthesi6 A la morphine et pentobarbital et ayant subi unc opkration fan-t8me (O.S.) ou une dknervation chirurgicale des chemor6cepteurs aortiyues (A.D.), nous avons evalue la reponse a une hypoxie d'une durCe de 15 min. Brarant la pkriode temsin, alors que Je chien respire de l'air ambiant, nous n'avons pas not6 de difference entre les chiens O.S. et A.D. quant aux paramktres cardio-vasculaires et respiratoires. Chez le chien tkmoin, l'hypoxie (Pao2 cte 30 mnlde Hg environ) est accompagnke d'une augmentation significative de la frkquence cardiaque ( 1-71 f 7 batt min-1, moyenne f S.E.M.) et du debit cardiaque (+25 f 10 ml kg-1 min-1). CRez l7anima1 A.D., on observe dans ces conditions unc augmentation significativement plus faible de la frkquel~ce cardiaque (+ 29 f . 6 batt min-1) et une dimimution du dkbit cardiaque (-16 f 12 an1 kg-1 min-1). Les modifications de la frkquence et du debit cardiaque produites par l'hypoxie sont differentes dp < 8.05) entre les deux types de prepar...