Search for pulmonary arterial chemoreceptors in the cat, with a comparison of the blood supply of the aortic bodies in the newborn & adult animal.

1. Electrophysiological and histological techniques have been employed to search for pulmonary arterial chemoreceptors in kittens and cats.2. In cats, impulses were recorded from vagal fibres arising from chemoreceptors in the aortico-pulmonary region. The receptors were identified by their response to hypoxia, and their location was investigated by comparing the effects of injecting drugs at various sites in the pulmonary and systemic circulations. In only one of a large number of experiments did a chemoreceptor appear to receive pulmonary rather than systemic arterial blood.3. No chemoreceptor impulses were evoked when a segment of the pulmonary artery was perfused as described by Duke, Green, Heffron & Stubbens (1963).4. The vasculature of the aortico-pulmonary bodies was displayed by micro-dissection following injection of coloured gelatin masses, and the bodies were examined histologically. In the new-born kitten, the pulmonary artery invariably furnished a branch to some aortic bodies but the vessel frequently anastomosed with systemic arteries. As post-natal development proceeded the vessel became occluded, and in most kittens more than a month old and in forty-one of forty-three cats the aortic bodies were supplied wholly by systemic arteries.5. It was concluded that a pulmonary arterial supply to aortic bodies in the adult animal is an uncommon variation owing to the abnormal persistence of a foetal condition.6. Results indicated that the nomenclature introduced by Howe (1956) is, with slight modification, a useful method of classifying the various groups of aortic bodies according to their position, blood supply and innervation.