Responses to catecholamines and nerve stimulation of the perfused rete tibiotarsale and associated blood vessels in the hind limb of the Mallard (Anas platyrhynchos).

The rete tibiotarsale, which is a functional arterio-venous heat exchanger, and its associated blood vessels were perfused in situ and the responses to epinephrine (E), norepinephrine (NE), and perivascular nerve stimulation (NS) were studied. The vasoconstrictor response of the arterial shunt, which bypasses the rete, was significantly greater than in adjacent segments of the same artery. The constrictor responses to E, NE, and NS were reversibly blocked by the alpha-blocker phentolamine. The rete arteries were also capable of vasoconstriction, but during simultaneous perfusion of the arterial shunt and the rete arteries, stimulation with NE and E stopped perfusate flow in the shunt while the flow in the rete arteries increased. Segments of the large vein and rete veins were unresponsive to NE, E, and NS. The results support the previously reported morphological evidences for a sphincteric action of the shunt artery, but not of the shunt vein.