Insulin sensitizers improve the GLP-1 secretion and the amount of intestinal L cells on high-fat-diet-induced catch-up growth.

Abstract

The aim of this study was to investigate whether insulin resistance can result in impaired glucagon-like peptide (GLP)-1 secretion and to determine whether insulin-sensitizing drugs could improve the secretion of GLP-1 in catch-up growth rats. Male Sprague Dawley rats were used to establish a catch-up growth model. At the end of weeks 6 and 14, these rats were euthanized to measure energy intake, body weight, plasma triacylglycerol, and nonesterified fatty acid. Fat mass percentage was analyzed by dual-energy x-ray absorptiometry scan. The GLP-1 concentrations were measured by enzyme-linked immunosorbent assay, the glucose infusion rates were measured by hyperinsulinemic-glucose clamp experiment. Quantification of the GLP-1 positive cells in distal ileum was done by immunohistochemical staining method. The L cell line NCI-H716cells were treated invitro with palmitate acid, the cells' viability, the carnitine palmitoyl transferase-1, and the insulin signaling pathway were detected. Rats fed a high-fat diet rats had rapidly developed insulin resistance, impaired incretin effect, and a reduction in the number of intestinal Lcells. The insulin sensitizers, metformin and pioglitazone, improved insulin resistance and the concentration of circulating GLP-1, increased the relative number of intestinal Lcells to a certain degree. Invitro, the NCI-H716cell viability was decreased and impaired insulin signaling pathway with palmitate acid treatment, metformin treatment could reverse these effects, whereas pioglitazone could not. Insulin resistance caused by a high-fat diet could result in reduced GLP-1 secretion; the insulin sensitizing drugs were able to improve the incretin effect in catch-up growth rats.