Developmental expression of neurokinin A and functional neurokinin-2 receptors in lung

Peribronchial smooth muscle constriction causes airway stretch, an important mechanical force in developing lung. Little is known about factors influencing these spontaneously active muscle elements. We measured contractile activity of neurokinin (NK) receptors on fetal intrapulmonary smooth muscle by tracheal perfusion assay (n = 11). Injecting either capsaicin or the NK2 receptor agonist [NLE10]NKA resulted in significant (P < 0.05) bronchoconstriction. A specific NK2 receptor antagonist inhibited constriction caused by endogenous tachykinins released by capsaicin. We then examined NK2 receptor (n = 44) and NKA (n = 23) ontogeny in human lung. NKA immunostaining was identified in peribronchial nerves in samples with gestational age > 12 wk. NK2 receptor protein was identified in peribronchial and perivascular smooth muscle. These results indicate that endogenous tachykinins released by the developing lung act via NK2 receptors to cause smooth muscle constriction. We speculate that tachykinins could modulate lung development.