Action of Lobeline and Capsaicine on Afferent Endings in the Pulmonary Artery of the Cat

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Abstract
A comparison has been made of the anatomical localization and some of the characteristics of the visceral afferent endings stimulated by capsaicine, lobeline, and phenyldiguanide. The reflex hypotensive responses to these drugs have been measured following injection into the right atrium and different positions of the pulmonary artery tree in cats anesthetized with α-chloralose. In comparison with the magnitude of the hypotensive responses to capsaicine, lobeline, and phenyldiguanide from the right atrium, the response to capsaicine and lobeline was small or absent on injection into the right or left branch of the pulmonary artery at the level of the hilum. The response to phenyldiguanide was the same on injection at these two positions. The latent period between the injection and the reflex responses to capsaicine and lobeline, and the sensitivity of these responses to blocking doses of sodium pentobarbital and procaine hydrochloride were the same. Tetraethylammonium chloride will block the reflex action of lobeline in doses that have little effect on the reflex action of capsaicine. It is concluded that, in the cat, the capsaicine-and lobeline-sensitive receptors have a similar distribution and are probably situated in the pulmonary artery and the extrapulmonary part of its main branches and that these are anatomically separate from those stimulated by phenyldiguanide.