Neurogenic pathways mediating ascending and descending reflexes at the porcine ileocolonic junction

We studied the pharmacology of the neural pathways mediating the responses of ileo- and coloileo-colonic junction (ICJ) to regional distension in ten anaesthetized pigs. Using manometric pullthroughs and a sleeve sensor, we f ound the ICJ demonstrated sustained tone that was resistant to tetrodotoxin . Ileal distension decreased ICJ pressure by 22.2 +/- 10.1% (11.9 +/- 2.7-1 0.1 +/- 2.6 mmHg; P=0.002) and colonic distension augmented ICJ pressure by 23.5 +/- 8.6% (12.8 +/- 1.5-15.6 +/- 2.1 mmHg; P=0.02). Bethanecol and N o mega-nitro-L-arginine methyl ester (L-NAME) increased ICJ pressure (P=0.002 , P=0.01, respectively). Sodium nitroprusside and isoproterenol reduced ICJ pressure (P=0.004, P=0.02, respectively). In the presence of L-NAME, the e arly inhibitory ileo-ICJ response was abolished, while early and late inhib itory responses were abolished by further addition of propranolol but not b y the addition of hexamethonium, atropine, prazosin or yohimbine. The excit atory colo-ICJ response was replaced by inhibition in the presence of L-NAM E. We concluded that: 1 the porcine ICJ displays myogenic tone which is influenced by excitatory muscarinic and inhibitory nitrergic and beta adrenergic pathways 2 an inhibitory ileo-sphincteric reflex mediated by nitrergic and beta adre nergic postganglionic neural pathways 3 both excitatory and inhibitory neurogenic colo-sphincteric reflexes exist , and the excitatory pathway involves nitrergic neurotransmission.