[Regulation of the tracheobronchial and lung vascular system: innervation and receptors].

The regulation of airway smooth muscle shows species variation. The common embryologic origin of the lung and the gut is evidenced by the fact that the morphology and function of innervation, ganglion cell population, smooth muscle cells and receptors are similar to analogous structures in the gastrointestinal tract. Human airway smooth muscle possesses the following anatomic, morphologic and functional characteristics: cholinergic excitatory nerves, non-adrenergic non-cholinergic (NANC) inhibitor nerves, non-cholinergic non-adrenergic excitatory nerves, no adrenergic nerves, an ultrastructural morphology of the ganglia, similar to the one in the gastro intestinal tract, smooth muscle cell-to-cell connection of the gap junction or nexus type, a possible spontaneous myogenic activity, Beta-2-receptors with inhibitory effect and Alpha-1-receptors with excitatory effect. The pulmonary vascular bed is a low pressure system. Pulmonary vascular tone is influenced and probably regulated by multiple neurohumoral factors. These include the autonomic nervous system and a variety of vasoactive peptides and lipides. The autonomic neurogenic influences include the alpha- and beta-adrenergic and cholinergic components, as well as a third, non-adrenergic non-cholinergic component which may be mediated by the neuropeptide Vasoactive Intestinal Polypeptide (VIP). Lung peptides - some present in neuroendocrine cells - have potent actions (relaxation or constriction) on pulmonary vessels and may participate in regulating vascular tone. Leukotriens and other biological active lipides generally constrict pulmonary vessel and promote microvascular permeability.