Tracheal smooth muscle responses to substance P and neurokinin A in the piglet

cheal smooth muscle responses to substance P and neurokinin A in the piglet. J. Appl. Physiol. 72(3): 1090-1095, 1992.-The tachykinins substance P (SP) and neurokinin A (NKA) have been-shown to induce airway smooth muscle contraction in ma-ture animals, and the enzyme neutral endopeptidase (NEP) modulates this effect. We evaluated maturation of SP- and NKA-induced tracheal smooth muscle contraction and modula-tion of their effects by NEP in anesthetized, paralyzed, and artificially ventilated piglets <4 days, 2-3 wk, and 10 wk of age. Tracheal smooth muscle tension was measured in vivo from an open tracheal segment by use of a force transducer. Intrave-nous SP caused a dose-dependent increase in tracheal tension in all three age groups; however, the response in c&day-old piglets was significantly weaker than in 2- to 3- and lo-wk-old piglets. NKA caused a dose-dependent increase in tracheal ten