Gut peptides in gastrointestinal motility and mucosal permeability
Abstract: Gut regulatory peptides, such as neuropeptides and incretins, play important roles in hunger, satiety and gastrointestinal motility, and possibly mucosal permeability. Many peptides secreted by myenteric nerves that regulate motor control are also produced in mucosal epithelial cells. Derangements in motility and mucosal permeability occur in many diseases. Current knowledge is fragmentary regarding gut peptide actions and mechanisms in motility and permeability.This thesis aimed to 1) develop probes and methods for gut permeability testing, 2) elucidate the role of neuropeptide S (NPS) in motility and permeability, 3) characterize nitrergic muscle relaxation and 4) characterize mechanisms of glucagon-like peptide 1 (GLP-1) and the drug ROSE-010 (GLP-1 analog) in motility inhibition.A rapid fluorescent permeability test was developed using riboflavin as a transcellular transport probe and the bisboronic acid 4,4'oBBV coupled to the fluorophore HPTS as a sensor for lactulose, a paracellular permeability probe. This yielded a lactulose:riboflavin ratio test.NPS induced muscle relaxation and increased permeability through NO-dependent mechanisms. Organ bath studies revealed that NPS induced NO-dependent muscle relaxation that was tetrodotoxin (TTX) sensitive. In addition to the epithelium, NPS and its receptor NPSR1 localized at myenteric nerves. Circulating NPS was too low to activate NPSR1, indicating NPS uses local autocrine/paracrine mechanisms.Nitrergic signaling inhibition by nitric oxide synthase inhibitor L-NMMA elicited premature duodenojejunal phase III contractions in migrating motility complex (MMC) in humans. L-NMMA shortened MMC cycle length, suppressed phase I and shifted motility towards phase II. Pre-treatment with atropine extended phase II, while ondansetron had no effect. Intestinal contractions were stimulated by L-NMMA, but not TTX. NOS immunoreactivity was detected in the myenteric plexus but not smooth muscle.Food-intake increased motility of human antrum, duodenum and jejunum. GLP-1 and ROSE-010 relaxed bethanechol-induced contractions in muscle strips. Relaxation was blocked by GLP-1 receptor antagonist exendin(9-39) amide, L-NMMA, adenylate cyclase inhibitor 2´5´-dideoxyadenosine or TTX. GLP-1R and GLP-2R were expressed in myenteric neurons, but not muscle.In conclusion, rapid chemistries for permeability were developed while physiological mechanisms of NPS, nitrergic and GLP-1 and ROSE-010 signaling were revealed. In the case of NPS, a tight synchrony between motility and permeability was found.
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