Insight into the biological role of secretin, the first hormone identified in 1902
Researchers from University of Copenhagen and University of Cambridge have uncovered a role of the first hormone ever identified, secretin in humans undergoing bariatric surgery.
118 years after its first discovery, a new physiological mechanism of the hormone secretin have been uncovered. PhD student Ida Modvig explains: “Our study demonstrates for the first time that secretin is increased after bariatric surgery probably due to a set of glucose-sensing secretin cells located in the distal part of the small intestine. Furthermore, our data suggest that secretin regulate pancreatic hormone secretion and that may contribute to improve glycemic control."
Uncovering the mechanism of bariatric surgery may be exploited as therapeutic to treat obesity and type 2 diabetes.
The study was led by Assistant Professor Nicolai J. Wewer Albrechtsen and Professor Jens Juul Holst and was made possible by a close collaboration between the NNF Center for Basic Metabolic Research, Department of Biomedical Sciences, NNF Center for Protein Research, University of Copenhagen and University of Cambridge.
The study is published in International Journal of Obesity
Abstract
Objectives: Gastrointestinal hormones contribute to the beneficial effects of Roux-en-Y gastric bypass surgery (RYGB) on glycemic control. Secretin is secreted from duodenal S-cells in response to low luminal pH, but it is unknown whether its secretion is altered after RYGB and if secretin contributes to the post-operative improvement in glycemic control. We hypothesized that secretin secretion increases after RYGB as a result of the diversion of nutrients to more distal parts of the small intestine, and thereby affects islet hormone release.
Methods: A specific secretin radioimmunoassay was developed, evaluated biochemically, and used to quantify plasma concentrations of secretin in 13 obese individuals before, 1 week after and 3 months after RYGB. Distribution of secretin and its receptor was assessed by RNA-sequencing, mass-spectrometry and in situ hybridization in human and rat tissues. Isolated, perfused rat intestine and pancreas were used to explore the molecular mechanism underlying glucose-induced secretin secretion and to study direct effects of secretin on glucagon, insulin and somatostatin secretion. Secretin was administered alone or in combination with GLP-1 to non-sedated rats to evaluate effects on glucose regulation.
Results: Plasma postprandial secretin was more than doubled in humans after RYGB (P<0.001). The distal small intestine harbored secretin expressing cells in both rats and humans. Glucose increased secretion of secretin in a sodium-glucose co-transporter dependent manner when administered to the distal part but not into the proximal part of the rat small intestine. Secretin stimulated somatostatin secretion (fold change: 1.59, P<0.05) from the perfused rat pancreas but affected neither insulin (P=0.2) nor glucagon (P=0.97) secretion. When administered to rats in vivo, insulin secretion was attenuated and glucagon secretion increased (P=0.04), while blood glucose peak time was delayed (from 15 min to 45 min) and gastric emptying time prolonged (P=0.004).
Conclusion: Glucose-sensing secretin cells located in the distal part of the small intestine may contribute to increased plasma concentrations observed after RYGB. The metabolic role of the distal S-cells warrants further studies.