Noradrenergic Inhibition of the Goat Carotid Body

Abstract

Circulating catecholamines are considered to be respiratory stimulants in humans. This conclusion is based on studies in which intravenous infusion of norepinephrine or epinephrine produced ventilatory stimulation (Cunningham, et al., 1963; Heistad et al., 1972). Because the respiratory stimulation was diminished during hyperoxia, it was concluded that the carotid bodies were responsible for the reflex effect. Studies of norepinephrine and epinephrine in non-human species have revealed complex and sometimes conflicting effects on the carotid body and ventilation. Joels and White (1968) found tht in anesthetized and decerebrate cats, these agents stimulate ventilation, an effect eliminated by carotid sinus nerve transection. Folgering et al. (1982) found that norepinephrine and epinephrine produced transient inhibition followed by excitation of carotid chemoreceptor afferent neural discharge frequency in cats. Although similarly complex effects were found in rabbits (Matsumoto et al., 1981), Bisgard et al. (1979) found primarily inhibition but also excitation of the carotid body in dogs. More recently, the possibility of a prominent alpha-2 adrenergic inhibitory mechanism in the cat carotid body has been described (Kou et al., 1991).