Attenuated Sympathetic Activity and Its Relation to Obesity in MSG Injected and Sympathectomized Rats

In order to characterize the role of sympathetic activity in obesity, we repeatedly assessed sympathetic activity via power spectral analyses of heart rate variability in the same subjects at 7, 11, 25, and 60 weeks, using monosodium glutamate (MSG)-induced obese and control rats. The effects of lower sympathetic activity on obesity were also evaluated. Fat mass in MSG rats was already higher at 7 weeks, but the sympathetic activity did not differ between 7 and 25 weeks. Between 25 and 60 weeks, the increase in fat mass, food efficiency, and body weight gain was higher in MSG rats. The increase in sympathetic activity between 25 and 60 weeks and sympathetic activity at 60 weeks were lower in MSG rats. Fat mass at 60 weeks was inversely correlated with changes in sympathetic activity between 25 and 60 weeks. Reduced plasma epinephrine levels by bilateral adrenal demedullation induced increase of fat mass. In summary, an attenuated increase of sympathetic activity with age may partly be responsible for aggravated obesity in MSG rats. Additionally, reduced sympathetic activity per se induced obesity in rats. These results suggest that lower sympathetic activity contributes to obesity in rats.

Preliminary study of insulin resistance induced by neonatal monosodium glutamate treatment in normal Wistar rats / 中国药理学通报

AIM To study the glucose and lipids metabolism and insulin sensitivity of MSG rats during their growing period, and to evaluate the effects of insulin sensitizer pioglitazone on the model rats. METHODS Body weights were measured regularly, and glucose and insulin tolerance tests were taken. In their 3 and 10 months old, rats were given insulin sensitizer pioglitazone orally, then the effects on serum glucose, triglyceride, cholesteral, free fatty acid and insulin concentrations were determined. RESULTS Compared with normal rats, a slight but significant increase of glucose in MSG rats was revealed. The serum triglyceride, cholesteral, free fatty acid and insulin concentrations were significantly higher in model rats. Moreover, gluconeogenesis increased significantly, and insulin tolerance showed abnormal. However, glucose tolerance was nearlly normal. Pioglitazone could ameliorate all these metabolic disorders. CONCLUSION Obesity and insulin resistance were induced by injecting monosodi- um glutamate (MSG) to neonatal Wistar rats. Piogli- tazone can significantly improve the insulin sensitivity of Msc rats. These results suggested that MSG obese rats can be used as an easily accessible and inexpensive insulin resistance animal model for evaluating the efficacy and mechanisms of antidiabetic agents.