Regional distribution and subcellular localization of catecholamines in the frog heart.

Abstract 1. 1. The distribution of epinephrine (E) and norepinephrine (NE) in sinus venosus (SV), atria and ventricle was studied in two species of frogs, two species of toads and one species of newts. 2. 2. Frogs and toads were found to contain E as the predominant catecholamine (CA) in all parts of the heart. 3. 3. Determinations of dopamine (DA), made in Rana pipiens , showed high concentrations of this amine in the pacemaker region (i.e. SV). 4. 4. The subcellular distribution of E and NE was studied in this latter species, using ultracentrifugation techniques. Most E present was found in the large particulate fraction (10,000 g ) and in the final filtrate. The microsomal (100,000 g ) fraction contained about equal proportions of E and NE. 5. 5. Histochemical studies on whole mount preparations of atria and SV of Rana pipiens , using the formaldehyde condensation technique for monoamines, showed that all catecholamines were present within nerve fibres. 6. 6. No CA-containing fluorescent cells could be demonstrated in these structures. It is concluded that the sympathetic fibers in the frog heart are properly “adrenergic” in that they contain predominantly E, in contrast to fibers in the hearts of all other vertebrate species studied which are noradrenergic containing predominantly NE. 7. 7. It is suggested that dopaminergic fibers may be present in the pacemaker regions of the heart.