Exenatide challenge in oral glucose tolerance test is insufficient for predictions of glucose metabolism and insulin secretion after sleeve gastrectomy (SG) in obese patients with type 2 diabetes: a pilot study to establish a preoperative model to estimate β-cell function following augmented glucagon-like peptide-1 secretion after SG.

The postoperative increase in glucagon-like peptide-1 (GLP-1) is the main factor to improve glucose metabolism following sleeve gastrectomy (SG) in obese patients with type 2 diabetes. We investigated whether the β-cell responsiveness to an injection of exogenous GLP-1 in the preoperative period could determine the postoperative glucose tolerance in 18 patients underwent SG. In the preoperative period, a regular oral glucose tolerance test (OGTT) and an exenatide-challenge during OGTT (Ex-OGTT) were performed to evaluate the β-cell function and its responsiveness to GLP-1. The postoperative glucose tolerance was evaluated by another regular OGTT performed at 3 months after SG. The significant decrease in glucose levels with enhanced secretions of insulin and GLP-1 was observed in OGTT at 3 months after SG. The area under the curve of glucose from 0 to 120 minutes (AUC glucose) and the insulinogenic index (I.I.) in OGTT at 3 months post-SG were significantly improved compared to those in preoperative period, but comparable with those in Ex-OGTT. AUC glucose and I.I. in OGTT at 3 months post-SG were significantly correlated with not only those in Ex-OGTT, but also those in the preoperative regular OGTT. Conversely, the correlations calculated by the Spearman's ρ were stronger in the latter than the former. This exenatide-challenge protocol might be useful to estimate glucose tolerance and insulin secretion after SG, however, it may be insufficient to improve predictability of a patient who is likely to achieve a significant benefit on glucose metabolism from receiving SG.