Modification of gut-islet secretions after Roux-En-Y gastric bypass (RYBG) surgery contributes to its metabolic and anti-diabetic benefits. However, there is limited knowledge on tissue-specific hormone distribution post-RYGB surgery and how this compares with best medical treatment (BMT). In the present study, pancreatic and ileal tissues were excised from male Zucker-Diabetic Sprague Dawley (ZDSD) rats 8-weeks after RYGB, BMT (daily oral dosing with metformin 300mg/kg, fenofibrate 100mg/kg, ramipril 1mg/kg, rosuvastatin 10mg/kg and subcutaneous liraglutide 0.2mg/kg) or sham operation (laparotomy). Insulin, glucagon, somatostatin, PYY, GLP-1 and GIP expression patterns were assessed using immunocytochemistry and analyzed using ImageJ. After RYGB and BMT, body weight and plasma glucose were decreased. Intestinal morphometry was unaltered by RYGB, but crypt depth was decreased by BMT. Intestinal PYY cells were increased by both interventions. GLP-1- and GIP-cell counts were unchanged by RYGB but BMT increased ileal GLP-1-cells and decreased those expressing GIP. The intestinal contents of PYY and GLP-1 were significantly enhanced by RYGB, whereas BMT decreased ileal GLP-1. No changes of islet and beta-cell area or proliferation were observed, but the extent of beta-cell apoptosis and islet integrity calculated using circularity index were improved by both treatments. Significantly decreased islet alpha-cell areas were observed in both groups, while beta- and PYY-cell areas were unchanged. RYGB also induced a decrease in islet delta-cell area. PYY and GLP-1 colocalization with glucagon in islets was significantly decreased in both groups, while co-staining of PYY with glucagon was decreased and that with somatostatin increased. These data characterize significant cellular islet and intestinal adaptations following RYGB and BMT associated with amelioration of obesity-diabetes in ZDSD rats. The differential responses observed and particularly those within islets, may provide important clues to the unique ability of RYGB to cause diabetes remission.

The incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are rapidly degraded by dipeptidyl peptidase-4 (DPP-4) to their major circulating metabolites GLP-1(9-36) and GIP(3-42). This study investigates the possible effects of these metabolites, and the equivalent exendin molecule Ex(9-39), on pancreatic islet morphology and constituent alpha and beta cells in high-fat diet (HFD) fed mice. Male Swiss TO-mice (6-8 weeks-old) were maintained on a HFD or normal diet (ND) for 4 months and then received twice-daily subcutaneous injections of GLP-1(9-36), GIP(3-42), Ex(9-39) (25 nmol/kg bw) or saline vehicle (0.9% (w/v) NaCl) over a 60-day period. Metabolic parameters were monitored and excised pancreatic tissues were used for immunohistochemical analysis. Body weight and assessed metabolic indices were not changed by peptide administration. GLP-1(9-36) significantly (p<0.001) increased islet density per mm(2) tissue, that was decreased (p<0.05) by HFD. Islet, beta and alpha cell areas were increased (p<0.01) following HFD and subsequently reduced (p<0.01-p<0.001) by GIP(3-42) and Ex(9-39) treatment. While GLP-1(9-36) did not affect islet and beta cell areas in HFD mice, it significantly (p<0.01) decreased alpha cell area. Compared to ND and HFD mice, GIP(3-42) treatment significantly (p<0.05) increased beta cell proliferation. Whilst HFD increased (p<0.001) beta cell apoptosis, this was reduced (p<0.01-p<0.001) by both GLP-1(9-36) and GIP(3-42). These data indicate that the major circulating forms of GLP-1 and GIP, namely GLP-1(9-36) and GIP(3-42) previously considered largely inactive, may directly impact pancreatic morphology, with an important protective effect on beta cell health under conditions of beta cell stress.

Kisspeptin is a neuropeptide recognised for a pivotal role within the reproductive system, but potentially important endocrine metabolic effects are less well understood. We examined effects of twice-daily intraperitoneal administration of saline vehicle or kisspeptin-10 (25 nmol/kg), for 21 days, on glucose homeostasis, energy balance, circulating hormones as well as the morphology-function of enteroendocrine and islet cells in high-fat diet (HFD) fed female mice, with normal diet (ND) mice as an additional control group. Kisspeptin-10 decreased body weight, blood glucose and energy intake to ND levels. HFD increased circulating follicle-stimulating hormone (FSH) levels, which were further enhanced by kisspeptin-10 along with luteinising hormone (LH) concentrations. Neither HFD nor kisspeptin-10 affected progesterone or corticosterone. In the ileum, kisspeptin-10 decreased crypt depth and restored villi length to ND control levels, as well as increasing the proportion of glucose-dependent insulinotropic polypeptide (GIP) positive cells when compared to HFD mice and glucagon-like peptide-1 (GLP-1) positive cells compared to ND mice. Peptide YY (PYY) immunoreactivity was unaltered by HFD or kisspeptin-10. Plasma GIP was unchanged but circulating GLP-1 and PYY were reduced to ND levels. Within the pancreas, total islet, beta- and alpha-cell areas were similar in all mice, but kisspeptin-10 intervention restored relative insulin area to ND levels. Glucagon radius, an indicator of peripherally located alpha-cells, was reduced in HFD mice but normalised by kisspeptin-10 alongside elevated glucagon-islet area. Notably, beta-cell proliferation was increased by kisspeptin-10 with no alteration in beta-cell apoptosis. Overall, we reveal a previously uncharacterised diverse metabolic role for kisspeptin in directly modulating the gut–pancreatic axis.

Aim: Estrogens regulate energy balance and glucose homeostasis, but whether they coordinate endocrine changes across the gut–pancreas axis in obesity remains unclear. This study examined whether ethinyl estradiol (EE2) improves metabolic control in obese diabetic mice through combined effects on pancreatic islets and intestinal enteroendocrine cells. Methods: Female ob/ob mice received EE2 (4,000 ng/mL) or vehicle in drinking water for 21 days. Body weight, food intake, glucose levels, glucose tolerance, pancreatic islet composition, and ileal enteroendocrine cell populations were assessed using biochemical assays and immunohistochemistry. Results: EE2 significantly reduced body weight and energy intake and produced sustained lowering of blood glucose with markedly improved glucose tolerance and reduced terminal insulin levels. EE2 increased islet density and beta-cell proliferation and shifted islet size distribution toward larger islets, consistent with enhanced islet growth. Alpha-cell area was significantly reduced, indicating improved insulin–glucagon balance. Peptide YY (PYY)-positive cells within pancreatic islets were markedly increased, whereas somatostatin (SST)-positive cells were unchanged. In the ileum, EE2 significantly reduced crypt depth and increased the number of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP)-positive enteroendocrine cells, particularly within crypt regions, indicating enhanced incretin cell abundance. These coordinated changes across the gut and pancreas were associated with improved glucose control and reduced hyperinsulinaemia. Conclusions: EE2 improves metabolic control in obese diabetic mice through linked changes in pancreatic islet cell composition and intestinal incretin-producing cells. By increasing beta-cell renewal, reducing alpha-cell area, and enhancing GLP-1, GIP, and PYY expression, estrogen establishes a gut–pancreas endocrine environment that supports glucose homeostasis in obesity.