Pulmonary Vasoconstriction Elicited by Stimulation of the Hypothalamic Integrative Area for the Defense Reaction

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Abstract
Changes in the pulmonary circulation evoked by stimulation of the hypothalamic integrative area for the defense reaction were studied in 22 cats anesthetized with a chloralose-urethane mixture. Pulmonary arterial pressure and flow, left and right atrial pressures, aortic pressure, arterial flow to the skinned hind limb, and heart rate were all significantly increased. The calculated pulmonary vascular resistance was also significantly increased. The rise in pulmonary vascular resistance was abolished by bilateral stellectomy or by hexamethonium infusion; it was not affected by bilateral cervical vagotomy. Therefore, the increase in pulmonary vascular resistance was mediated by the thoracic sympathetic nerves. The increase in pulmonary arterial flow was mainly caused by an increase in heart rate; a small rise in calculated stroke volume also occurred.

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