Relaxation effect of marmin on guinea pig tracheal smooth muscle via NO-independent mechanisms

ObjectiveTo investigate the relaxation mechanims of marmin on epithelium of guinea pig isolated trachea smooth muscle (TSM).MethodsThe study was conducted using in vitro isolated-trachea experimental. The guinea pig isolated trachea were incubated in Krebs solution-containing organ bath and supplied with a mixed gas of O2: CO2 (95%:5%).ResultRemoval of tracheal epithelium was associated with significant increases in the potencies of histamine and methacholine to contract guinea pig TSM. The pD2 value of histamine increased from 6.04±0.08 on epithelial-intact to 6.32±0.06 on epithelial-denuded (P < 0.05). The pD2 value of methacholine also increased from 5.85±0.09 on epithelial-intact to 6.15±0.07 on epithelial-denuded (P < 0.05). Marmin exhibited relaxation effects on TSM induced by methacholine (3×10−5 mol/L) and histamine (3×10−5 mol/L). Inhibition of prostaglandin E2 (PGE2) through incubation with indomethacin could reduce the relaxation effect of marmin (P < 0.05) on methacholine- and histamine-induced contractions. However, no significant differenceswere shown in methylene blue, Nω-nitro-L-arginine (L-NNA) and propranolol-incubated TSM.ConclusionsThe results suggest that marmin has relaxation effect on TSM which is epithelial-dependent through the release of PGE2. However, nitric oxide, cGMP and β2-adrenergic-mediated relaxation were not involved.