Regulation of the Release of Dopamine and Norepinephrine from Rabbit Carotid Body

Abstract

The discovery of multiple neuroactive agents in type I (glomus) cells of the carotid body and the demonstration that natural stimuli evoke their release constitute important advances that have reshaped contemporary views of chemotransmission in this organ. It is now generally accepted that carotid sinus nerve (CSN) discharge is influenced by such putative transmitter agents as acetylcholine (ACh), dopamine (DA), norepinephrine (NE), substance P (SP), met-enkephalin (ME), and perhaps others (1,2). A crucial step in defining the roles of these putative transmitters is to identify conditions that affect their metabolism, as well as the cellular mechanisms which allow for modulation of one transmitter by another. In the present experiments, we have investigated the effects of natural and pharmacological stimuli on the release of DA and NE from the rabbit carotid body. In related experiments, the effects of chronic sympathectomy and the role of a classical second messenger (cAMP) in the catecholamine (CA) release process was also examined. The data suggest that distinct mechanisms in the chemosensory tissue can regulate independently the release of DA and NE. These mechanisms appear to be influenced oppositely by cAMP and they are subject to control by the sympathetic innervation to the organ.