Mechanisms of epidermal growth factor-induced contraction of guinea pig airways

We investigated the functional effects of epidermal growth factor (EGF) on guinea pig airways in vitro. EGF (3 ng/ml to 1 microgram/ml) induced a concentration-dependent contraction in epithelium-denuded strips. The average maximal contraction was 0.64 +/- 0.1 g (mean +/- S.E., for n = 27), which was 72.0 +/- 9.5% of the 100 mM KCl-induced contraction. The EC50 was 12.3 +/- 1.6 ng/ml. The presence of the epithelium significantly suppressed the EGF-induced contraction (P < 0.01). EGF-induced contraction was abolished by cyclooxygenase inhibitors (indomethacin and ibuprofen) and a 5-lipoxygenase inhibitor, 2-(12-hydroxydodeca-5,10-diynyl)-3,5,6-trimethyl-1,4-benz oqu inone (AA-861). It was also inhibited by a leukotriene-receptor antagonist, 8-[p-(4-phenylbutyloxy)benzoyl]amino-2-(tetrazol-5-yl)-4-oxo -4H-1-benzopyran hemihydrate (ONO-1078) but not affected by a thromboxane A2-synthetase inhibitor, (E)-3-[4-(1-imidazolylmethyl)phenyl]-2-propenoic acid (OKY-046) or a thromboxane A2-receptor antagonist, 9,11-epithio-11,12-methano-thromboxane A2 (ONO-3708). A phospholipase A2 inhibitor (mepacrine) inhibited the EGF-induced contraction but a diacylglycerol-lipase inhibitor, 1,6-di-(O-(carbamoyl)cyclohexanone oxime)hexane (U-57908) and a phospholipase D inhibitor (wortmannin) did not affect it. A tyrosine kinase inhibitor (genistein) abolished it. Measurement of prostanoids showed that EGF (300 ng/ml) did not increase the prostaglandin F2 alpha level in either epithelium-intact or epithelium-denuded strips. In epithelium-intact strips, EGF significantly increased the prostaglandin E2 concentration (P < 0.01). These results suggest that EGF causes contraction of guinea pig airway smooth muscle by activating tyrosine kinase followed by phospholipase A2 activation, and that arachidonic acid metabolites, especially leukotrienes, may have important roles in this contraction.