Chronic Hypoxia Enhances Expression of Catecholamine Biosynthesizing Enzymes in Rat Carotid Body

Catecholamines, dopamine and norepinephrine, are present in a significant amount in the carotid body of many animal species (Fidone et al, 1980; Fitzgerald et al, 1983). Dopamine is synthesized in glomus cells since the presence of the rate limiting enzyme in catecholamine synthesis, tyrosine-hydroxylase (TH), has been clearly demonstrated. Moreover, hypoxia is known to increase dopamine release (Fidone et al, 1982), norepinephrine content (Hanbauer et al, 1981; Verna et al, 1993), and activity of TH in carotid body, and to induce the expression of TH-mRNA (Czyzyk-Krzeska et al, 1992). However, the presence of epinephrine in the carotid chemoreceptors remains controversial probably because of the difficulty in detecting small amounts of this substance.