Control of the Human lleocaecal Junction: An in vitro Analysis of Adrenergic and Non-Adrenergic Non-Cholinergic Mechanisms

Abstract

Circular muscle strips from the human lleocaecal junction developed myogenic tone (sustained resting tension) in vitro and showed an obvious component of relaxation in response to electrical field stimulation. These features are considered typical of sphincteric muscle because circular muscle strips from terminal ileum 1-2 cm proximal to the junction and from the caecum or ascending colon 1-2 cm distal to the junction developed little or no tone and showed predominantly contractile responses to electrical-field stimulation. In 18 out of 29 specimens, junctional strips showed excitatory responses to adrenaline or noradrenaline. The relaxation of junctional strips was non-adrenergic non-cholinergic (NANC) in nature. Nitric oxide appears to be involved in the NANC relaxation.

Effects of gastrin‐releasing peptide (GRP) on the mechanical activity of the human ileocaecal region in vitro

“…The tonic component, depending on the location from where the preparations had been excised, decreased in orad and aborad directions. This is in agreement with experiments of McKirdy et al 14 and favours a sphincteric role of the ileocaecal junction in man. In all strips, the phasic-rhythmic activity could be abolished by blockade of L-type calcium channels with nifedipine, whereas the tonic component was sensitive to the nitric oxide donor sodium nitroprusside.…”

In vitro and in vivo effects of nitric oxide synthase inhibitors and nitric oxide inactivators on the South American opossum ileocolonic junction*

“…These findings are consistent with previous reports on the dog, cat and human ICJ as well as in human and North American opossum lower oesophageal sphincter (LOS) 15–21 indicating that NO synthase activity is required for the NANC nerve‐induced relaxations. The fact that NADPH‐diaphorase activity, which is a surrogate marker for NO synthase activity, was detected in myenteric plexus neurones and fibres and in varicose nerve fibres around the circular smooth muscle layer, but not in smooth muscle cells, suggests that NO synthase inhibitors exert a prejunctional action.…”

Differential effect of nitric oxide synthase inhibition on sigmoid colon longitudinal and circular muscle responses to nicotine and nerve stimulation in vitro

“…Tetrodotoxin has been shown to abolish rapidly and reversibly all responses to EFS in human proximal and distal colonic tissues, including sigmoid colon, indicating that these responses are neurally mediated; spontaneous contractions, however, persist with tetrodotoxin 11,12 . Inhibitory responses to EFS can be demonstrated more clearly when smooth muscle tone is raised pharmacologically with substance P 6 or carbachol 8 , when a clear relaxation response can be seen.…”