Quantitative morphometric analysis of substance P, vasoactive intestinal peptide, and neuropeptide Y in guinea pig airway.
As putative neurotransmitters of nonadrenergic, noncholinergic (NANC) nerves, neuropeptides have various actions on airway smooth muscle. However, the magnitude of their effects depends on airway level and may be related to the density of innervation. This study quantifies the distribution of substance P (SP), vasoactive intestinal peptide (VIP), and neuropeptide Y (NPY), in smooth muscle of different airway levels. Guinea pig airways (n-4) from trachea through small bronchi were divided into eight levels: upper, middle, and lower trachea (UT, MT, LT), extrapulmonary bronchi (EXB), proximal (PA) and distal (DA) axial bronchi, and the pooled 2nd to 5th generations from the proximal (P2-5) and distal (D2-5) axial bronchi (see diagram). Sections from each level were immunocytochemically labeled for SP, VIP, and NPY. Density of innervation was determined by measuring the number of nerve fibers per mm2 (n/mm2) of airway smooth muscle. SP is present at all levels but highest in smaller airways. VIP is most abundant in the trachea and absent in smaller airways. NPY is present at all levels but highest in the trachea. Thus, the density of neuropeptide innervation is regionally heterogeneous for each neuropeptide. The distribution described is consistent with physiological studies on the actions of neuropeptides on airway smooth muscle at different levels.
Respiratory-system-disorders; Pulmonary-system-disorders; Lung-disorders; Lung-function; Airway-obstruction; Airway-resistance; Laboratory-animals; Laboratory-testing; Nerves; Neurotransmitters; Peptides; Muscles; Vasoactive-agents; Neuromuscular-system; Intestinal-cells; Nerve-fibers; Physiological-measurements; Cytochemistry