VIP and chronic obstructive pulmonary disease: VPAC1 was particularly elevated in alveolar macrophages of COPD patients.207 VPAC2 receptor was activated by VIP, and inhibited the CSE-induced cytotoxicity of rat lung alveolar L2 cells.208 Increased serum VIP levels are associated with acute exacerbation of COPD patients.209 VIP has significant therapeutic potential in the treatment of COPD.208 How, it clinical application might be limited because of the short half-life of plasma after intravenous administration and the difficulty of routes.210,211 VIP (3-month inhaled treatment) was performed in severe COPD patients.