Proliferation and repair of guinea pig tracheal epithelium after neuropeptide depletion and injury in vivo

Neuropeptides stimulate airway epithelial cell proliferation and migration in vitro, but the role of neuropeptides in the repair of the epithelium after injury in vivo is not clear. We studied epithelial proliferation and repair in 83 male Hartley guinea pigs. Animals received capsaicin weekly for 3 wk to deplete airway neuropeptides. One week later, the dorsal aspect of the trachea was injured with a metal stylette. Animals were killed 1 h to 1 wk later, after which epithelial cell proliferation was assessed for the presence of proliferating cell nuclear antigen (PCNA). PCNA labeling was < 3% in noninjured animals. PCNA labeling increased substantially in the first 72 h after injury in control animals but was significantly decreased in capsaicin-treated animals within and adjacent to the site of injury. PCNA labeling increased opposite to the injury site in both control and capsaicin animals over the first 72 h. We conclude that neuropeptide depletion significantly attenuates both epithelial cell proliferation and repair in the first 72 h after mechanical injury to the trachea. However, neuropeptide depletion did not slow the ultimate repair of tracheal mucosal injury. Proliferation of epithelial cells in response to injury occurs throughout the airway, even away from the injury site.