Effect of duodenal mucosal blood flow on duodenal alkaline secretion in rats

The duodenal mucosal bicarbonate secretion

The duodenal lumen is exposed to aggressive factors with a high potential to cause damage to the mucosa. Bicarbonate secretion by the duodenal mucosa is accepted as the primary important defense mechanism against the hydrochloric acid intermittently expelled from the stomach. The present work concerns both the influence of the central nervous system and the effects of the hormone melatonin on duodenal bicarbonate secretion in anesthetized rats in vivo as well as effects of melatonin on intracellular calcium signaling by duodenal enterocyte in vitro examined in tissues of both human and rat origin. The main findings were as follows: Melatonin is a potent stimulant of duodenal mucosal bicarbonate secretion and also seems to be involved in the acid-induced stimulation of the secretion. Stimulation elicited in the central nervous system by the alpha1-adrenoceptor agonist phenylephrine induced release of melatonin from the intestinal mucosa and a four-fold increase in alkaline secretion. The melatonin antagonist luzindole abolished the duodenal secretory response to administered melatonin and to central nervous phenylephrine but did not influence the release of intestinal melatonin. Central nervous stimulation was also abolished by synchronous ligation of the vagal trunks and the sympathetic chains at the sub-laryngeal level. Melatonin induced release of calcium from intracellular stores and also influx of extracellular calcium in isolated duodenal enterocytes. Enterocytes in clusters functioned as a syncytium. Overnight fasting rapidly and profoundly down-regulated the responses to the duodenal secretagogue orexin-A and the muscarinic agonist bethanechol but not those to melatonin or vasoactive intestinal polypeptide.

Brief communication: smoking and duodenal blood flow

Smoking promotes an increase in both the incidence and the recurrence of duodenal ulcers, but the mechanisms responsible for its adverse effects on the duodenal mucosa are still poorly understood. The aim of the present study was to investigate the effect of chronic cigarette smoking on duodenal blood flow. In 20 dyspeptic patients (10 non-smokers and 10 smokers) with endoscopically normal duodenum, mucosal blood flow was measured in the duodenal bulb by laser Doppler flowmetry during endoscopy. Basal bulbar perfusion was found to be significantly lower (P < 0.05) in smokers. Our results suggest that duodenal blood flow is reduced in heavy smokers. This may promote duodenal damage because of both local ischaemia and the reduced secretion of protective bicarbonate.