RESPONSES OF LUNG PARENCHYMA AND AIRWAYS TO TACHYKININ PEPTIDES IN PIGLETS

The tachykinin peptides substance P (SP) and neurokinin A (NKA) have been shown to induce tracheal smooth muscle contraction in piglets, and the enzyme neutral endopeptidase has been shown to modulate this effect. In these studies, we compared the SP and NKA responsiveness of piglet airways and lung parenchymal tissues in anesthetized paralyzed open-chest piglets 2-3 wk old, partitioning total lung resistance (RL) into airway resistance (Raw) and tissue resistance (Rti). During tidal breathing, pressure was measured at the trachea and in two alveolar regions by means of alveolar capsules. Intravenous administration of SP caused 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 accounted for >50% of RL. The responses of Rti and Raw to NKA were negligible and were always significantly weaker than those to SP. These results indicate that both central airways and tissue contractile elements respond vigorously to SP, but not to NKA, in maturing piglets.