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 longitud inal muscle strips from horse duodenum, ileum and colon. Circular smoo th muscle of the small intestine was highly responsive, large intestin e circular smooth muscle less so, while longitudinal muscle from all g ut segments was much less sensitive. pD2 values and intrinsic activiti es on small intestine circular muscle indicated differences in recepto r distribution between the duodenum and ileum: NK3 and a smaller numbe r of NK2 receptors being present in the duodenum, and NK2 receptors pr edominating in the ileum. Notwithstanding this, eledoisin and neurokin in B were the most active substances on duodenum and ileum, respective ly. These findings suggest that tachykinins may play a role in equine gastrointestinal pathophysiology.