The route of antigen delivery determines the airway and lung tissue mechanical responses in allergic rats

Background Previous results have shown tissue constriction in allergic anim als following inhalation of an antigen. Further studies have demonstrated a differing response pattern in airway and parenchymal mechanics following i nhaled (i.h.) or intravenous (i.v.) delivery of methacholine (MCh). Object ive The purpose of this study was to compare the acute allergic resp onse in airway and parenchymal mechanics following i.h. and i.v. antigen ch allenge. Methods Brown Norway rats were sensitized to ovalbumin (OVA). Rats were ana esthetized, paralysed, and thoracotomized,and lung input impedance (ZL) bet ween 0.5 and 21 Hz was measured using small-amplitude pseudo-random oscilla tions at control, after saline, and for up to 1 h after either i.h. (n = 7) or i.v. (n = 5) administration of OVA. ZL was evaluated in terms of airway resistance (Raw) and inertance (Iaw), and a constant phase tissue parenchy mal damping (G) and elastance (H). Results Following i.h. OVA challenge elevations were found in Raw [192 +/- 32(SE) %], G (223 +/- 21%), and H (141 +/- 5%). Raw showed higher elevation after i.v. challenge (418 +/- 57%), whereas the elevation in G (278 +/- 30 %) and H (130 +/- 4%) was approximately equal to those seen following inhal ation of an antigen. Conclusions Delivery (i.v.) of an antigen produces a significantly higher r esponse in airway resistance, whereas inhaled antigen results in a mixed ai rway and parenchymal response.