This study aims at investigating the possible beneficial effect of succinic acid dimethyl ester (SAD), injected intraperitoneally (5.0 micromol/g body wt.), upon the metabolic and hormonal response to a 60 min exercise in both fed and overnight starved rats. In fed rats, the injection of SAD minimized the fall in plasma D-glucose concentration, and the increase in plasma lactate, beta-hydroxybutyrate, free fatty acid and glycerol concentrations, otherwise provoked by exercise. SAD, however, failed to prevent the decrease in plasma insulin concentration and liver glycogen content caused by exercise. Starved rats displayed lower plasma D-glucose and insulin concentrations and higher plasma beta-hydroxybutyrate and free fatty acid concentrations than fed rats. The body weight, liver weight and paraovarian fat weight, as well as the glycogen content of both liver and heart were also decreased in the starved rats. In the latter animals, the injection of SAD again opposed the exercise-induced increase in plasma beta-hydroxybutyrate, free fatty acid and glycerol concentrations, and again failed to prevent the more modest decreases in plasma insulin concentration and liver glycogen content caused by exercise in the starved, as distinct from fed rats. These findings suggest that, independently of any obvious change in plasma insulin concentration, SAD minimizes the exercise-induced mobilization and enhanced utilization of endogenous nutrients, especially fatty acids and glycerol produced by hydrolysis of triglycerides in adipose tissue, presumably through its capacity to act as an oxidizable nutrient in various cell types and as a gluconeogenic precursor in hepatocytes.

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