Evidence for the involvement of endogenous substance P in the motor effects of capsaicin on the rat urinary bladder.

[pro4,trp7,9,Leu11]SP-(4-11), a substance P (SP) antagonist, selectively antagonized contractions produced by either capsaicin or SP on the rat isolated urinary bladder. These experiments provide direct evidence indicating that the motor effects of capsaicin on rat urinary bladder are attributable, at least in part, to the release of endogenous SP.