ABSTRACT
As a neuropeptide with wide distribution, vasoactive intestinal polypeptide (VIP) is a likely neurotransmitter or neuromodulator. Though first isolated from small intestine, VIP had earlier been discovered in the lung as a vasodilator peptide. VIP-containing neurons are localized in the tracheobronchial smooth muscle layer, around submucosal mucous and serous glands, in the lamina propria, and in the walls of pulmonary and bronchial arteries. Numerous reports document the colocalization of VIP with other neuropeptides or neurotransmitters. Specific receptors for VIP have been identified in membrane preparations of normal mammalian and human lungs and in human lung tumor cells, including small cell carcinoma cell lines. Strong evidence points to adenylyl cyclase stimulation and cyclic adenosine monophosphate production as the dominant mode of action of VIP in most instances. In the superior cervical ganglion and adrenal chromaffin cells, relatively high concentrations of VIP increased the breakdown of phosphoinositides to inositol phosphates, enhancing the intracellular mobilization of Ca2+.
