Indblik i den biologiske rolle af sekretin – det første hormon der blev identificeret

118 år efter dets opdagelse, er der blevet fundet en ny fysiologisk funktion af hormonet sekretin. Ph.d.-studerende Ida Modvig forklarer: "Vores studie demonstrerer for første gang, at sekretin øges efter en vægttabsoperation. Dette skyldes formentlig en gruppe af glukose-følsomme sekretin-celler, der er lokaliseret i den nederste del af tyndtarmen. Derudover viser vores data, at sekretin regulerer bugspytkirtlens hormonsekretion og at den måske bidrager til at øge den glykemiske kontrol."

Opdagelsen af øget sekretin udskillelse efter vægttabsoperationer kan måske bruges til at behandle fedme og type 2-diabetes.

Studiet blev ledet af adjunkt Nicolai J. Wewer Albrechtsen og professor Jens Juul Holst. Det blev muliggjort af et tæt samarbejde mellem Novo Nordisk Fondens Center for Basic Metabolic Research, Biomedicinsk Institut, NNF Center for Protein Research, Københavns Universitet og Cambridge University.

Studiet er publiceret i International Journal of Obesity.

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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.