The sources of plasma catecholamines in the American eel, Anguilla rostrata

The origin of the catecholamines (CAs) in the systemic blood of the American eel, Anguilla rostrata, was studied by three approaches: (1) determination of the CA content of tissues suspected to release large quantities of dopamine, norepinephrine, and/or epinephrine into the circulation; (2) measurement of local CA titers in selected regions of the cardiovascular system; and (3) removal of tissues with high CA concentrations, followed by determination of its impact on stimulated CA release. Large quantities of all three CAs were found in the walls of the posterior cardinal veins, from their caudal origin within the opisthonephric kidney to their termination in the ductus Cuvieri. Near the ductus Cuvieri, the CA concentration was 1-3 orders of magnitude above that in other tissues. In this region, which contains the presumed adrenal medulla equivalent, occur the highest plasma levels of the CAs. Strong CA release also in the opisthonephric kidney region raises the question if these CAs affect locally the kidney functions, and/or via the hepatic portal vein (which originates in this region), the liver. Other organs (especially brain and heart) contain CA concentrations high enough to potentially affect the CA level in the systemic blood, if instantly released. However, neither partial removal of the brain nor hypophysectomy, "adrenomedullectomy," Stanniectomy, or urophysectomy had an appreciable impact on stimulated CA release. Together with previous data, these findings show that in the eel (a) the region of the presumed adrenal medulla equivalent is the most important source of all three CAs in systemic plasma; (b) that strong CA-stimulated CA release also occurs outside this region; and (c) that the pituitary, forebrain, and midbrain are not necessary for the CA-stimulated CA release.