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Prolonged effects of airway epithelial denudation on the mechanical properties and proliferation of airway smooth muscle in the guinea pig

University of British Columbia

The epithelium serves a multitude of functions in the airway wall. More than just acting as a physical barrier, it secretes chemical mediators which regulate smooth muscle function. Injury to the airway epithelium, and with it a loss of these functions, may contribute to the excessive airway narrowing to contractile stimuli observed in asthmatics. However, the long term effects of epithelial denudation on the mechanical properties or proliferation of airway smooth muscle have not been investigated. We hypothesized that epithelial removal from guinea pig tracheal rings would enhance stress generation, shortening and proliferation of airway smooth muscle over time. Paired epithelium intact (Ep+), and denuded (Ep-) rings were incubated in organ culture for 0, 1, 3, or 7 days, followed by measurement of passive isometric stress at Lmax (S₀), maximum active isometric stress (Smax), and maximum isotonic shortening (ΔLMax) to acetylcholine stimulation. Contractile dose responses to histamine and carbachol, and relaxant dose responses to isoproterenol, were also determined. In parallel, paired tracheal rings, immunohistochemical staining for 5-bromo-2'-deoxyuridine was used to calculate the proliferation index (PI). Epithelium removal led to a significant increase in Smax, and ΔLMax to acetylcholine in addition to increases in, the Smax and sensitivities to histamine measured o n ∙ ∙ ∙ ∙ ∙ 0, 1, and 7, but not on day 3. Some epithelial regeneration of a stratified squamous type was evident in epithelium denuded rings measured on day 3, and thus may account for the lack of increase on day 3. The addition of flurbiprofen, a cyclooxygenase inhibitor, did not mimic the effects of epithelial removal suggesting that other epithelium-derived factors may account for the differences. Epithelial removal did not alter constriction to carbachol or relaxation to isoproterenol. No differences in the smooth muscle cross-sectional area or PI were detected between Ep+ and Ep- rings regardless of day, suggesting that epithelium removal and regeneration had no significant effect on the proliferation of smooth muscle. These results demonstrate that the enhanced force generation and shortening caused by epithelial removal is not due to smooth muscle hypertrophy or hyperplasia. In addition, the rapid re-epithelialization and time dependent altered smooth muscle mechanics in this thesis establishes a useful model for studying the effects of airway remodeling in vitro.

Thesis/Dissertation

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2009-05-26

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http://hdl.handle.net/2429/8239

Experimental Medicine

University of British Columbia

UBCV

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