[Neuropeptides and respiratory diseases: prospects in the treatment of asthma]

The autonomic nervous system includes, side by side with the sympathetic and parasymathetic systems, a third, non-adrenergic and non-cholinergic system called NANC. The mediators in this system are peptides acting as neurotransmitters, i.e. neuropeptides. The NANC system has two components: bronchodilator and bronchoconstrictor. The bronchial relaxant system, called non-adrenergic inhibitory system, has several neurotransmitters, viz.: vasoactive intestinal peptide (VIP), isoleucine histidine peptide (IHP) and methionine histidine peptide (MPH), all derived from a common precursor: pre-pro VIP. MHP has been described in man and IHP in some animal species. VIP relaxes the bronchial smooth muscle, is vasodilator and exerts cellular effects in phagocytes, lymphocytes and mast cells. VIP receptors are present on cells. The other component, called non-cholinergic excitatory system, has tachykinins as neuromediators, including substance P, neurokinins A and B, neuropeptide K and calcitonin gene related peptide (CGRP). Substance P contracts the bronchi, increases mucus secretion, dilates vessels and also exerts cellular effects in lymphocytes and phagocytes. Tachykinins act through receptors 3 types of which are now known: NK 1, NK 2 and NK 3. Other neuropeptides have been isolated, including galanin, neuropeptide Y, bombesin, gastrin releasing peptide, enkephalins and katacalcin. The coexistence, in pre- and post-synaptic positions, of the conventional mediators (noradrenaline, acetylcholine) and neuropeptides leads to the concept of co-transmission and makes the notion of nerve impulse transmission more complex. The development of neuropeptide agonists and antagonists opens new therapeutic prospects in the management of asthma.