Increase in substance P levels in the lung of old rats

Substance P levels in the lung of young (3-month-old), adult (12-month-old), senescent (20-month-old) and aged (28-month-old) male Wistar rats were determined by radioimmunoassay. Levels of substance P were constant until 28 months of age when these become significantly higher (approximately more than 2 times, p less than 0.001) than the values found in younger rats. Whether the increase of substance P content in the lung of old rats may reflect changes in the density of substance P containing nerve fibres or in the content of the peptide in single nerve fibres is discussed.