Abstract
Although most bodily serotonin (5-HT) is stored in intestinal enterochromaffin (EC) cells, the mechanism of its release is only now being elucidated. It has previously been reported that such stimuli as luminal acidification or exposure of both sides of a rabbit duodenal mucosal sheet to certain autonomic agonists stimulate release from the mucosal surface in the Ussing chamber model. The hypothesis in the present study is that acid acts only on the mucosal surface, whereas neural receptor agonists and antagonists act specifically on the serosal surface, as would be predicted by the location of acid in the gut lumen and nerve terminals at the bases of the EC cells. 5-HT release was measured by radioimmunoassay from the mucosal surface bathing solution. Duodenal mucosal sheets were exposed separately on the mucosal or serosal surfaces to acid (citric phosphate buffer, pH 5) or to isoproterenol (10 −5 M). The effect of atropine (10 −6 M) and propranolol (10 −6 M) on acid-stimulated mucosal release was studied by combining luminal acid stimulation with one of these antagonists, on either the mucosal or serosal surface. The results demonstrate significant ( P < 0.01) mucosal serotonin release (56 ± 9 ng cm −2 hr −1) only with mucosal acidification. On the other hand, isoproterenol causes significant ( P < 0.05) serotonin release (12.4 ± 3 ng cm −2 hr −1) only when introduced onto the serosal surface. Finally, the antagonists, atropine and propranolol, blocked acid-stimulated serotonin release only when added to the serosal surface. Since acid-induced serotonin release has been shown to be partially mediated by cholinergic and β-adrenergic mechanisms, these findings suggest interconnection of mucosal acid receptors with submucosal neurons which mediate serotonin release by acting on the basal surface of the enterochromaffin cell.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.