In vitro effects of tachykinins on the smooth musculature of horse gut

The contractile effects of the tachykinins eledoisin, substance P and neurokinin A and B were investigated in vitro on circular and longitudinal muscle strips from horse duodenum, ileum and colon. Circular smooth muscle of the small intestine was highly responsive, large intestine circular smooth muscle less so, while longitudinal muscle from all gut segments was much less sensitive. pD₂ values and intrinsic activities on small intestine circular muscle indicated differences in receptor distribution between the duodenum and ileum: NK₃ and a smaller number of NK₂ receptors being present in the duodenum, and NK₂ receptors predominating in the ileum. Notwithstanding this, eledoisin and neurokinin B were the most active substances on duodenum and ileum, respectively. These findings suggest that tachykinins may play a role in equine gastrointestinal pathophysiology.