Moderate Exercise Restores Pancreatic Beta-Cell Function and Autonomic Nervous System Activity in Obese Rats Induced by High-Fat Diet

Abstract

Background/Aims: Metabolic syndrome has been identified as one of the most significant threats to human health in the 21^st century. Exercise training has been shown to counteract obesity and metabolic syndrome. The present study aimed to investigate the effects of moderate exercise training on pancreatic beta-cell function and autonomic nervous system (ANS) activity in rats fed a high-fat diet (HFD). Methods: Weaning rats were divided into four groups: rats fed a standard chow or HFD (sedentary, Control-SED and HFD-SED; or exercised, Control-EXE and HFD-EXE, respectively). Exercised rats ran (from 21- to 91-days-old) for 60 minutes (3 times/week) over a 10-week period. Glucose and insulin tolerance tests were performed. Pancreatic islets were isolated to study glucose-induced insulin secretion (GIIS). Parasympathetic and sympathetic nerve electrical signals were measured, and liver samples were processed and histologically analyzed. Results: Exercise prevented obesity, insulin resistance, and liver steatosis as well as improved total cholesterol, ALT, and AST levels. Islets from HFD rats showed insulin hypersecretion which was ameliorated by exercise. Exercise decreased vagal nerve activity in the HFD-EXE group and increased the activity of the sympathetic nervous system in both exercised groups. Conclusion: Exercise prevents obesity and liver steatosis and restores pancreatic beta-cell function and ANS activity in HFD-obese rats.

Low-intensity and moderate exercise training improves autonomic nervous system activity imbalanced by postnatal early overfeeding in rats

“…The data of the current research reveal, for the first time, that higher vagal nerve activity is observed in obese rats induced by early overfeeding. Our group also observed this feature in other different model of obesity [19,20,27,34], in all of these obesity model high fasting insulinemia and insulin resistance were observed. The method used in the present work cannot discriminate afferent from efferent signals; however, the firing rates from control rats are very similar to those reported by other authors [35,36].…”

“…In previous studies, using the same exercise training protocol applied throughout life, we showed that obese rats induced by high-fat diet restores the imbalanced autonomic function beyond other metabolic dysfunctions [27]. Similar results were obtained in rats fed hypercaloric diets that ran voluntarily [39].…”

“…Running protocols, including running speeds and times, were set to induce moderate-intensity exercise training, promoting a 50-70% total oxygen uptake (VO 2max ) for each animal, independent of age. The running protocols used have been described previously [27,28] with some modifications. The anaerobic threshold of the rats is approximately 20 m.min -1 and was used to delimit the maximal velocity reached in the training program.…”

“…The sessions were increased to 20 min at 12 m × min -1 for the subsequent sessions. The rats in the group exercised from days 21–90 had an adaptation time of two weeks, and the rats in the 21–50 day group and the 60–90 day group had an adaption time of one week, as previously reported [27]. The running sessions were performed in the afternoon.…”

HPA axis and vagus nervous function are involved in impaired insulin secretion of MSG-obese rats

“…After a stabilization of the signal over the course of 2 min, 20 record frames of 15 s were randomly chosen from each animal for spike counting. The average number of spikes was used to calculate the rate of nerve firing for each rat (Gomes et al 2013).…”