Dihydrocapsaicin treatment depletes peptidergic nerve fibers of substance P and alters mast cell density in the respiratory tract of neonatal sheep

In the present study we administered dihydrocapsaicin (DHC) to neonatal lam bs to deplete C-fibers of neuropeptides. We measured the density of substan ce P (SP)-fibers in nasal septum to assess the effectiveness of the treatme nt at 3, 9, and 21 days. The numbers of mast cells in the upper and lower r espiratory tract were determined at the same time points and histamine cont ent was determined from lung tissue. DHC treatment depleted SP-fibers for u p to the 21 day time point. This depletion was estimated as 85% in comparis on with controls. In vehicle-treated lambs, the density of SP-fibers decrea sed progressively with age, but not to the degree of DHC-treated lambs whos e SP-fibers were depleted from the initial 3-day measurement. In both, vehi cle- and DHC-treated lambs, numbers of mast cells increased progressively w ith time; however, the density of mast cells was augmented in the entire re spiratory tract of DHC-treated animals. Apparently, DHC treatment exerts a single and initial effect in increasing mast cells whereas time maintains a continuous influence; both factors exert their influence independently. De spite large numbers of mast cells in DHC-treated animals, histamine content in the lung had similar levels as controls. Our study provides fundamental data for a better understanding of conditions that may influence defense m echanisms dependent on the mast cell-nerve axis in the respiratory tract. ( C) 2000 Elsevier Science B.V. All rights reserved.