Influence of centrifugal sinus nerve activity on carotid body catecholamines: microphotometric analysis of formaldehyde-induced fluorescence.

The effects of centrifugal activity in the carotid sinus nerve (CSN) on the intensity of formaldehyde-induced fluorescence of carotid body were examined in cat. Measurements of intensity were obtained from 21 to 56 sections of each carotid body with a microscope photometer attached to a fluorescence microscope. Comparisons were made between the two carotid bodies removed from each cat. In one series of experiments, one carotid body (CSN intact) served as control, while the experimental carotid body was on the side on which centrifugal activity was increased by electrical stimulation of the peripheral end of the cut CSN. In a second series, centrifugal CSN activity was increased by hypoxemia; one CSN was transected (control) and the other was left intact (experimental). In untreated cats, fluorescence intensity was significantly higher on the side with increased centrifugal CSN activity. In cats treated with either MK486, which inhibits conversion of L-DOPA to dopamine, or reserpine, increased centrifugal CSN activity caused a significant decrease in intensity of type I cells. These findings indicate that centrifugal discharges regulate, in part, the synthesis and release of catecholamines by type I cells of the carotid body.