Epidermal growth factor-urogastrone (murine EGF-URO) caused concentration-dependent contractile responses in preparations of longitudinal and circular smooth muscle derived from guinea pig stomach. The actions of EGF-URO in these two preparations were distinguished in terms of the ability of indomethacin to block EGF-URO-mediated contraction completely in the longitudinal muscle preparation but not in the circular muscle preparation. The EC50 for EGF-URO was 2 to 5 nM in the longitudinal muscle preparations and 20 to 50 nM in the indomethacin-treated circular muscle preparation. The action of EGF-URO in the longitudinal preparation also was inhibited by ibuprofen, aspirin and by anti-inflammatory steroids possessing an 11-beta-hydroxyl; the corresponding steroids lacking the 11-beta-hydroxyl substituent were inactive. In contrast, little or no effect of the anti-inflammatory steroids on the EGF-URO-mediated response was observed in the indomethacin-treated circular muscle preparation. Partial inhibition (about 30%) of the EGF-URO-mediated contraction of the indomethacin-sensitive longitudinal preparation was caused by mepacrine and p-bromophenyl-acylbromide, whereas esculetine, tranylcypromine, prazosin, yohimbine and cyproheptadine had no effect. The action of EGF-URO in both preparations exhibited marked tachyphyllaxis, which could not be attributed either to the production of inhibitory factors or to the disappearance of EGF-URO from the organ bath. The response of both preparations required the presence of extracellular calcium and was inhibited largely (90%, longitudinal preparation) or in part (69%, indomethacin-treated circular preparation) by verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)