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 found the ICJ demonstrated sustained tone that was resistant to tetrodotoxin. Ileal distension decreased ICJ pressure by 22.2 ¿ 10.1% (11.9 ¿ 2.7-10.1 ¿ 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 Nw-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 early inhibitory ileo-ICJ response was abolished, while early and late inhibitory responses were abolished by further addition of propranolol but not by the addition of hexamethonium, atropine, prazosin or yohimbine. The excitatory colo-ICJ response was replaced by inhibition in the presence of L-NAME. 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 adrenergic postganglionic neural pathways (3) both excitatory and inhibitory neurogenic colo-sphincteric reflexes exist, and the excitatory pathway involves nitrergic neurotransmission.