Branchial vascularization in the eel: action of acetylcholine and adrenaline on the distribution of polymerizable resin in the different vascular compartments.

The current findings from gill vascular cast preparations in the eel emphasize the division in each primary lamella of the afferent vasculature into two efferent pathways: an arterial pathway (via the secondary lamellae and the efferent branchial artery to the dorsal aorta), a venous pathway (via the central lamellar compartment and the branchial vein to the sinus venosus). By the same technique two antagonist mechanisms have been shown presumably controlling the blood flow in both pathways. 1. Acetylcholine increases the filling of the central lamellar compartment by constricting the efferent arterial sphincters and therefore increases the venous return. 2. Epinephrine impairs the filling of the central lamellar compartment (by acting on alpha receptors) and dilates the arterial pathway (by acting on beta receptors). Therefore the stimulation of these two synergic receptors by epinephrine increases the systemic blood flow.