Vasomotion in chicken foot: dual innervation of arteriovenous anastomoses.

Blood exits the foot of the domestic chicken via two major venous routes: a counter-current network surrounding the major incoming artery and a large collateral vein. Between these two routes are numerous large collateral vein. Between these two routes are numerous anastomotic veins. Both venous routes drain capillaries and arteriovenous anastomoses (AVAs). Blood flow through the foot was measured on unanesthetized hens. Flow varies with ambient temperature: 0.2 ml/min at 5 degrees C, 2.2 ml/min at thermoneutrality, and 5.4 ml/min at 36 degrees C; the AVAs contribute 8, 26, and 63% to this flow, respectively. Flow through capillaries is reduced by alpha-adrenergic agonists and is increased by beta-adrenergic agonists. Blocking nerve conduction to the foot at thermoneutrality releases alpha-adrenergic tone and increase AVA flow. Faradic stimulation of foot nerves after adrenergic blockage increases AVA flow, but not capillary flow, suggesting active vasodilation of the AVAs. Such AVA vasodilation normally occurs during body heating, since AVA flow decreases after denervation. Dopaminergic or beta-adrenergic nerves are not involved in active vasodilatation, however, purinergic nerves may play a role. Thus AVAs have a functional dual innervation.