Abstract
Cervical vagal section is rapidly fatal to the guinea pig. The process is one of pulmonary hyperemia followed usually but not necessarily by transudation. Factors incidental to laryngeal paralysis or to tracheotomy are not implicated nor are the changes agonal. The changes must be due to afferent denervation since atropine does not induce or intensify the changes. Sympathetic hyperactivity is not involved; on the contrary, prior reduction of sympathetic tone intensifies or induces the change. Isopropylarterenol, a smooth muscle relaxant, prevents the effects of vagal section. The pulmonary changes following vagal section are, therefore, due to a loss of the sympathetic tone necessary to maintain normal smooth muscle tone in the bronchioles or pulmonary vessels. Since the loss of sympathetic activity results from section of sensory fibers in the vagus, it is reflex in origin.
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