Prokinetic effects of cisapride, naloxone and parasympathetic stimulation at the equine ileo‐caeco‐colonic junction

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Abstract
The electromyogram of the terminal ileum, the caecum and the proximal right ventral colon was recorded in fasted conscious ponies receiving intravenously equiactive doses of pilocarpine (0.05 mg/kg) and carbachol (0.01 mg/kg) as acetylcholine analogues; cisapride (0.1 mg/kg) and metoclopramide (2 mg/kg) facilitating acetylcholine release from myenteric neurones and naloxone (0.05 mg/kg) as an antogonist of the endogenous inhibitory opioid system. Both cisapride and naloxone induced typical migrating spike bursts in the colon associated with contractions of caecal body and caecal base. Both pilocarpine and carbachol stimulated the termination ileum but had opposite effects on the activity of the caeco-colonic segments which was decreased by pilocarpine and increased by carbachol. High doses of metoclopramide had weak and unspecific stimulator motor effects. It is conncluded that a true prokinetic effect at the equine ileo-caeco-colonic junction requires a motor profile which includes cooridination between contractions sequentially involving the body and the base of the caecum and migrating spike bursts on the proximal colon. Such changes in the motor profile were produced by cisapride and naloxone and to a lesser extent by carbachol.