Catecholamines in the carotid body are unaffected by hypercapnia.

In contrast to the increased content of dopamine and norepinephrine in rat carotid body during hypoxia (10% O2 in nitrogen) for 3 and 21 days, hypercapnia (8% CO2 in air) for 21 days failed to alter the catecholamine concentrations. DOPAC content was elevated in hypoxia whereas there were no significant changes in hypercapnia. This finding supports the view that the mechanisms of peripheral chemoreception differ, at least partly, in hypoxia and hypercapnia.