Tachykinins in the respiratory tract.

Tachykinins as substance P and neurokinin A belong to a family of peptides, which are released from airway nerves after noxious stimulation. They influence numerous respiratory functions under both normal and pathological conditions including the regulation of airway smooth muscle tone, vascular tone, mucus secretion and immune functions. For the most part the synthesis/release of tachykinins is associated with neuronal cells; nevertheless, inflammatory and immune cells can synthesize and release tachykinins under certain physiological conditions. Moreover, this second cellular source of tachykinins may play an important role in inflammatory airway diseases such as bronchial asthma or chronic obstructive pulmonary disease (COPD). Dual tachykinin (NK1 and NK2) receptor antagonists demonstrate a significant bronchoprotection and a possible future role in the development of novel therapeutic approaches. In addition, NK3 receptors could also possess a bronchoprotective action, however, their presence in the human respiratory tract still needs to be confirmed. The family of tachykinins has recently been extended by the discovery of a third tachykinin gene that encodes the previously unknown NK1 receptor selective tachykinins hemokinin 1, endokinin A and B. Together with other novel tachykinin peptides such as C14TKL-1 and virokinin further research is required to define their respiratory biological role in health and disease.