Gastric Bypass-Related Effects on Glucose Control, β Cell Function and Morphology in the Obese Zucker Rat

Roux-en-Y gastric bypass (RYGB) may improve beta cell function by mechanisms other than caloric restriction and body weight loss. We aimed to assess the impact of anatomical and hormonal alterations specific to RYGB on glucose homeostasis, β cell function and morphology.

Male Zucker(fa/fa) rats underwent either RYGB (n = 11) or sham surgeries (n = 10). Five of the shams were then food restricted and body weight matched (BWM) to the RYGB rats. Six male Zucker(fa/+) rats underwent sham surgery and served as additional lean controls. Twenty-seven days after surgery, an oral glucose tolerance test (OGTT) was performed and plasma levels of glucose, insulin and glucagon-like peptide-1 (GLP-1) were measured. Immunohistological analysis of pancreatic islets was performed, and GLP-1 receptor and PDX-1 mRNA content were quantified.

Shams consumed more food and gained more weight compared to both RYGB and BWM (p < 0.001). Hyperglycaemia was evident in ad libitum-fed shams, whilst postprandial glucose levels were lower in RYGB compared to the BWM sham group (p < 0.05). During the OGTT, RYGB rats responded with >2.5-fold increase of GLP-1. Histology revealed signs of islet degeneration in ad libitum-fed shams, but not in RYGB and sham BWM controls (p < 0.001). GLP-1 receptor and PDX-1 mRNA content was similar between the RYGB and BWM shams but higher compared to ad libitum shams (p < 0.05).

Combined molecular, cellular and histological analyses of pancreatic function suggest that weight loss alone, and not the enhancement of GLP-1 responses, is predominant for the short-term β cell protective effects of RYGB.