Immunochemical localization of type I VIP receptor and NK-1-type substance P receptor in rat lung

Peptidergic nerves in the respiratory tract release vasoactive intestinal peptide (VIP) and substance P (SP), which mediate physiological and immune functions. Antipeptide antibodies to type I VIP receptor (VIPR) and NK-1-type SP receptor (SPR) were used to identify these receptors in normal rat lungs. VIPRs and SPRs were detected on airway epithelium from the trachea to the respiratory bronchioles but not in alveoli, submucosal glands, or pulmonary smooth muscle, except for that of some pulmonary veins. VIPRs also were expressed on macrophages around capillaries, in tracheal and bronchial connective tissue, in alveolar walls, and in the subintima of pulmonary veins and some arterioles. The absence of receptors from airway smooth muscle and submucosal glands implies that mediation of some known effects of SP and VIP may be epithelial or macrophage dependent. Other types of VIPRs and SPRs on airway glands and smooth muscle may transduce direct effects. The similar localization of VIPRs and SPRs in rat lung suggests that VIP and SP may coordinately regulate some pulmonary functions.