Reflex changes on the pulmonary and systemic pressures elicited by stimulation of baroreceptors in the pulmonary artery.

• The action of sympathetic and parasynipathetic nerves on the pulmonary vessels is well known. However, until recently, it was thought that the circulation of blood in the lungs was achieved passively. Anatomical and pathological studies have shown that in cases of pulmonary hypertension there is a marked hypertrophy of the muscular coat of the pulmonary artery, which suggests an active vasoconstriction.-" Moreover, pressoreceptor-like structures were recently described in the pulmonary arteries, and Coleridge recorded impulses from some vagal fibers when the large branches of the pulmonary artery were distended. The present work was carried out in order to study the possibility of a pulmo-pnlmonary baroreceptor reflex mechanism in the regulation of the pulmonary circulation.