Plasma catecholamines in the lamprey: intrinsic cardiovascular messengers?

The widely scattered cardiovascular chromaffin cells of Petromyzon marinus appear to form an intrinsic control system of circulatory function. In response to blood-borne stimuli, a checkpoint-like accumulation of epinephrine cells in the heart releases its hormone; epinephrine, in turn, stimulates the release of norepinephrine, and probably also of dopamine, from other cardiovascular chromaffin cells. The myocardium seems to be a major target of norepinephrine. On the other hand, high disappearance rates of epinephrine and dopamine in the gills point to these organs as possible major targets of the latter two secretions. Carbon dioxide and hypovolemia are strong stimuli of catecholamine release.