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

Abstract

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.

Determinants of postprandial flow across the human ileocaecal junction: a combined manometric and scintigraphic study

“…The ability of the ICJ to regulate luminal flow has been debated in the literature for many years. While several studies in animals 1,3,21,22 and humans 4,5,23 confirmed the existence of a high‐pressure zone at the ICJ, data supporting the ability of this raised pressure zone to inhibit coloileal reflux are scarce. Furthermore, myotomy of the sphincter in dogs 24,25 and removal of the ICJ by right hemicolectomy in humans 26 failed to influence flow rates or transit times of chyme from the ileum to caecum.…”

“…The ileocolonic junction (ICJ) is reported to regulate flow between the terminal ileum and colon. Studies in both animals and humans have identified a high‐pressure zone within the ICJ that demonstrates sphincteric characteristics 1–5 . In animal models, ileal propagating sequences (PSs) have been temporally associated with caecal filling 6–8 .…”

The ileocolonic sphincter

“…An earlier study has reported inhibition of such contractions but this result is questionable due to the available recording method 13 . In a porcine model, 8 a more complex pattern of response was observed depending on the degree of distension. For low distending pressure, about one‐third of the responses were inhibitory whereas the remaining were excitatory.…”

“…In horse, a species with an extended caecocolonic segment the high‐pressure zone is only 6 mmHg over a distance of 5 cm 7 . In pig, a species also with a large caecocolonic segment, the high‐pressure zone is slightly larger yet less than that recorded in dog with a mean pressure of 15 mmHg over 3 cm length 8 . Manometric studies of the human ICS have yielded conflicting observations, with some investigators demonstrating a sustained high‐pressure zone 9,10 and others not demonstrating this 11–14 .…”

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

“…The ileocolonic junction also has intense nitrergic innervation in the dog (Boeckxstaens et al, 1990a(Boeckxstaens et al, , 1993bBogers et al, 1991;Leelakusolvong et al, 2002), cat (Mozhorkova et al, 1994), opossum (Matsuda et al, 1998), and pig (Kajimoto et al, 2000) that would contribute to the regulation of the ileocolonic transit of intraluminal contents. Muscarinic M 1 receptors also mediate nitrergic inhibitory responses in the rat intestine (Olgart and Iversen, 1999) and cat duodenum (Shikova and Kortezova, 2000).…”