Domperidone as a Tool to Assess the Role of Dopamine within Carotid Body Chemoreception

Abstract

The carotid bodies are composite receptors, i.e. hypoxia apparently acts upon glomus cells which are synaptically apposed to the sensory endings of primary afferent neurons, responsible for conveying the information to the medullary centers. Considerable effort has been directed to determine the transmitter(s) involved in signal transference between glomus cells and chemosensory nerve terminals. Dopamine is the putative transmitter that has received more attention, because of the following observations: i) glomus cells are characterized by their abundance in dense-core granules and strong formaldehyde-induced fluorescence, indicative of a high concentration of catecholamines (see Hess, 1975); ii) dopamine is the prevalent catecholamine in the carotid body of most species studied (see Fidone et al, 1983); iii) glomus cells possess the enzymes required for dopamine synthesis as well the transporter mechanisms for uptake of dopamine and its precursors (see Eyzaguirre & Zapata, 1984); iv) the dopamine content of the rat carotid body in situ is reduced in direct proportion to the severity and duration of hypoxia (Hellström et al, 1976; Hanbauer & Hellström, 1978); v) the dopamine content of the rabbit carotid body in vitro is reduced by hypoxic superfusates (Leitner, 1993); and vi) hypoxia induces dopamine release from rabbit and cat carotid bodies superfused in vitro (Fidone et al, 1982; Rigual et al, 1986; see also Zapata et al, 1996). These observations led to the proposal that dopamine may serve as the excitatory transmitter between glomus cells and chemosensory nerve terminals (see Gonzalez et al, 1994).