RESPONSES OF LUNG PARENCHYMA AND AIRWAYS TO TACHYKININ PEPTIDES IN PIGLETS

The tachykinin peptides substance P (SP) and neurokinin A (NKA) have b een shown to induce tracheal smooth muscle contraction in piglets, and the enzyme neutral endopeptidase has been shown to modulate this effe ct. In these studies, we compared the SP and NKA responsiveness of pig let airways and lung parenchymal tissues in anesthetized paralyzed ope n-chest piglets 2-3 wk old, partitioning total lung resistance (RL) in to airway resistance (Raw) and tissue resistance (Rti). During tidal b reathing, pressure was measured at the trachea and in two alveolar reg ions by means of alveolar capsules. Intravenous administration of SP c aused concentration-dependent increases in Rti and Raw and a decrease in dynamic lung compliance. Under baseline conditions, Rti contributed 74.6 +/- 1.9% (SE) of RL, and at any level of constriction, Rti accou nted for >50% of RL. The responses of Rti and Raw to NKA were negligib le and were always significantly weaker than those to SP. These result s indicate that both central airways and tissue contractile elements r espond vigorously to SP, but not to NKA, in maturing piglets.