Effect of exercise on body weight and insulin sensitivity following glucose loading in chronic leptin treated rats

Abstract

Leptin is known to increase glucose metabolism and energy expenditure while insulin increases glucose uptake into peripheral tissue. However, in obese and type 2 diabetes mellitus (T2DM) patients, high levels of both leptin and insulin are observed, indicating resistance to these two hormones in these individuals. It is unclear if elevated leptin levels are the cause of insulin resistance in these individuals. Physical exercise is known to be useful in the management of obesity and T2DM. It has been found that exercise can decrease bodyweight and increase glucose uptake in these individuals following exercise. This study aims to determine the effect of chronic leptin treatment and exercise on body weight, serum glucose and insulin levels of Sprague-Dawley rat. Eight-week old rats were treated with either intraperitoneal injection of normal saline (Control; n=8), or leptin (60 μg/kg body weight/day; Leptin; n=8), or leptin and exercise (60 μg/kg body weight/day plus running on a treadmill every other day for 30 minutes at a speed of 30 m/min with 10° inclinations; Leptin-exercise; n=8) or exercise only (running every other day for 30 minutes at a speed of 30 m/min with 10° inclinations on a treadmill; Exercise; n=8) for six weeks. Following six weeks of treatment, glucose challenge was performed by intravenous infusion of 100 mg/ml of glucose for 5 minutes. During the protocol, blood was drawn at 0, 5, 10, 15, 20, 25 and 30-min for estimation of serum glucose, and serum insulin levels. Data were analyzed using oneway ANOVA with post-hoc analysis and expressed as mean ± standard error of mean (SEM). Despite not statistically different in body weight between the groups, leptin group shows higher trend of mean body weight indicating treatment with leptin might induce leptin resistance in this group. Moreover, glucose clearance was also delayed in this group showing decreased insulin action associated with lower insulin level in leptin group. More importantly, exercise reversed the leptin effects by promoting glucose clearance. In conclusion, six weeks of daily leptin administration resulted in delayed glucose clearance, however, concurrent exercise prevented these effects of leptin by promoting glucose clearance signifying increase in insulin action.