Contraction of guinea pig trachea by epidermal growth factor – urogastrone

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Abstract
To evaluate further the action of epidermal growth factor – urogastrone (EGF–URO) in smooth muscle systems, we examined the effect of the peptide on guinea pig tracheal strips. The cumulative addition of EGF–URO to the organ bath resulted in a concentration-dependent tonic contraction without tachyphylaxis. The half-maximal contraction was obtained at 13 ± 3 ng/mL EGF–URO (2 nM). The maximum contraction at 100 ng/mL approached 60% of that induced by 1 μM histamine. No significant difference in the EGF–URO-induced contraction was observed in the presence or absence of a functional epithelium, Preincubation with 1 μM indomethacin for 20 min abolished the action of EGF–URO. The contractile effect of EGF–URO was not affected by yohimbine, propranolol, atropine, tetrodotoxin, and esculetin. However, mepacrine caused inhibition by 37 ± 7% (mean ± SEM for n = 3). Verapamil (10 μM) inhibited the EGF-induced response by 62 ± 5% (mean ± SEM for n = 4); the response was also absent in Ca-free (1 mM EGTA) buffer. However, the response was restored after the readdition of calcium. Our results suggest that EGF–URO can modulate tracheal smooth muscle contractility via a cyclooxygenase product and raise the possibility that EGF–URO might play a role in controlling pulmonary smooth muscle tone in vivo.