Chemoreceptor response to hypoxia and hypercapnia in catecholamine depleted rabbit and cat carotid bodies in vitro

The response of single chemoafferent fibres to hypoxic and hypercapnic stimulation was studied in vitro under different experimental conditions: 1. control, 2. 24 h after reserpinization (5 mg/kg iv) and 3. 18 h after iv injection of alpha-methyl-p-tyrosine (100 mg/kg in the rabbit, and 1. control and 2. 24 h after reserpinization (5 mg/kg ip) in the cat. The spontaneous activity was decreased by monoamine depletion. The amplitude of the response to hypoxia and to hypercapnia was decreased by reserpinization in the rabbit and in the cat, the change being less marked in the latter species. Similarly, treatment with alpha-methyl-p-tyrosine decreased the ability of chemoreceptors to respond to hypoxia and hypercapnia and, in a few instances, these receptors could only be excited by superfusion of nitrogen-equilibrated medium. These results emphasize to possible role of monoamine, and particularly dopamine, in modifying the sensitivity of arterial chemoreceptors to their natural stimuli.