Context
The hormone secretin (SCT) is released from intestinal S cells and acts via the SCT receptor (SCTR). Circulating SCT levels increase after Roux-en-Y gastric bypass surgery and have been associated with massive weight loss and high remission rates of type 2 diabetes (T2D) linked to these operations. Exogenous SCT was recently shown to reduce ad libitum food intake in healthy volunteers.

Objective
To understand SCT biology and its potential role in T2D pathophysiology, we examined the intestinal mucosal expression profile of SCT and SCTR and evaluated the density of S cells along the intestinal tract of individuals with T2D and healthy controls.

Methods
Using immunohistochemistry and messenger RNA (mRNA) sequencing, we analyzed intestinal mucosa biopsies sampled along the small intestine at 30-cm intervals and from 7 well-defined anatomical sites along the large intestine (during 2 sessions of double-balloon enteroscopy) in 12 individuals with T2D and 12 healthy controls.

Results
Both groups exhibited a progressive and similar decrease in SCT and SCTR mRNA expression and S-cell density along the small intestine, with reductions of 14, 100, and 50 times, respectively, in the ileum compared to the duodenum (used as reference). Negligible amounts of SCTR and SCT mRNA, as well as low S-cell density, were found in the large intestine. No significant differences were observed between the groups.

Conclusion
SCT and SCTR mRNA expression and S-cell density were abundant in the duodenum and decreased along the small intestine. Very low SCT and SCTR mRNA levels and S-cell numbers were observed in the large intestine, without aberrations in individuals with T2D compared to healthy controls.