The present study was undertaken to know whether the formation of inositol 1,4,5-trisphosphate (IP3) is increased by quick stretch, a dynamic mechanical stimulus in porcine coronary artery in order to inquiry the possibility that IP3 could mediate Ca2+ release in the stretch-induced contraction. Quick stretching of a helical strip of porcine coronary artery at a rate of 10 cm/sec, the amount of stretch equivalent to 140% of the initial muscle length (= 100%), and the stimulus period of 30 sec with 20-min intervals, produced delayed contraction. Quick stretching increased the content of IP3 about three-fold over the control basal level, which always preceded the contraction. A putative phospholipase C inhibitor, 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC), abolished the increase in the formation of IP3 and partially inhibited the stretch-induced contraction. The results suggest that quick stretching increases the formation of IP3 through a possible mechanism for activation of phospholipase C, which may lead to release of Ca2+ into myoplasm and to further activation of the contractile elements.