Vagal control of pulmonary vascular resistance in the turtle Chrysemys scripta

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Abstract
We have directly examined the control of pulmonary vascular resistance in the turtle Chrysemys scripta to determine the way in which pulmonary vasoregulation is achieved. The pulmonary circulation of the turtle Chrysemys scripta receives a strong excitatory cholinergic innervation from the vagus nerve. The major site of vasoconstrictor activity is in the extrinsic pulmonary artery proximal to the lung with only weak constrictor activity evident in the intrinsic arteries and arterioles within the lung parenchyma. No cholinergic innervation is evident in the segment of the extrinsic pulmonary artery proximal to the origin of the arterial ligament (ligamentum Botalli) and all vagally induced changes in flow resistance reside in the much narrower segment distal to this site. Vagal stimulation in an intact preparation produces sufficient constriction in the distal segment of extrinsic pulmonary artery to totally occlude pulmonary flow. The pulmonary arteries appear to be devoid of sympathetic innervation.