Aortic and carotid body chemoreception in prolonged hyperoxia in the cat

Abstract

Carotid body chemisensory response to hypoxia is attenuated as a result of prolonged normobaric hyperoxia (NH) in the cat. The effect of NH is likely to be due to high cellular P o2 and O 2-related free radicals. Accordingly, the effect would be less if O 2 delivery to the chemoreceptor tissue could be compromised. The aortic bodies, which appear to have less of a circulatory O 2 delivery, as suggested by their vigorous responses to a slight compromise of O 2 flow compared with those of the carotid body, could provide a suitable testing material for the hypothesis. We tested the hypothesis by studying both aortic and carotid body chemoreceptors in the same cats ( n=6) which were exposed to nearly 100% O 2 for about 60 h. These chemoreceptor organs were also studied in 6 control cats which were maintained in room air at sea-level. The cats were anesthetized and their carotid and aortic chemosensory fibers were identified by the usual procedure, and their responses to hypoxia and hypercapnia and to bolus injections (i.v.) of cyanide and nicotine were measured. In the NH cats, the carotid but not aortic chemosensory responses to hypoxia and cyanide were attenuated and to hypercapnia (both onset and steady state) augmented. The aortic chemoreceptors were stimulated by hypoxia, hypercapnia, cyanide and nicotine both in the NH and the control cats similarly. The results support the hypothesis that is presumably a higher tissue blood flow and hence a higher concentration of O 2-related free radicals which ultimately led to the specific attenuation of O 2 chemoreception in the carotid body.