Responses of goat ruminal musculature to substance P in vitro and in vivo.

A concentration-response curve obtained for contraction of goat rumen strips indicated that substance P (SP) is a very potent spasmogenic agent. In vivo, SP caused a dose-dependent inhibition of the extrinsic rumen contractions possibly due to an increase in ruminal smooth muscle tone, resulting in reflex inhibition. SP did not induce significant changes in heart rate. Further studies are necessary to elucidate a possible physiological role of SP in the modulation of forestomach motility.