Effect of Carbon Dioxide on the Structure of the Carotid Body A comparison between normoxic and hypoxic conditions

Abstract

Three types of hypoxia with different levels of carbon dioxide (hypocapnic, isocapnic, and hypercapnic hypoxia) have been called systemic hypoxia (Hirakawa et al., 1997). Recently, the changes in general morphology and in peptidergic innervation in the carotid bodies of rats exposed to systemic hypoxia were examined to evaluate the effect of arterial CO₂ tension (Kusakabe et al., 1998, 2000, 2002). The carotid bodies of the systemic hypoxic rats were found to be enlarged several fold, but the degree of enlargement was different for each (Kusakabe et al., 2003). The mean diameter of the hypercapnic hypoxic carotid bodies were smaller than the hypocapnic and isocapnic hypoxic carotid bodies. The vasculature in the carotid bodies of chronically hypercapnic hypoxic rats was found to be enlarged in comparison with that of normoxic control rats, but the rate of vascular enlargement was smaller than that in hypocapnic and isocapnic hypoxic carotid bodies. This indicates that the morphological changes in the hypoxic carotid bodies may depend on the arterial CO₂ tension. However this hypothesis may be restricted to the carotid bodies in hypoxic conditions. To clarify this we compared the morphological changes and those in the peptidergic innervation between the carotid bodies of the rats exposed to hypercapnic hypoxia and those exposed to normoxic hypercapnia.