Endocrine Abstracts

Aim: HMβ is a metabolite of leucine commonly used by athletes and in medical practice in order to increase muscle mass and/or minimize protein degradation. We have previously shown that chronic intake of HMβ increases GH synthesis and secretion in rats, which might account to its anabolic effect. However HMβ-treated rats, although normoglycemic, exhibited hyperinsulinemia, suggesting an apparent insulin resistance (IR) state. The present study attempted to investigate this possibility.

Methods: Rats were treated with HMβ (320 mg/kg BW) or vehicle, by gavage, for 4 weeks, during which the body weight was monitored. After this period, part of the animals was subjected to glucose tolerance test (GTT), and the remainder was sacrificed by decapitation for removal of the soleus and extensor digitorum longus (EDL) muscles to evaluate the GLUT4 content (GLUT4/g tissue), dry/wet weight ratio and cross-sectional area (CSA). Data were analyzed by unpaired Student’s t-test. The HMβ chronic administration resulted in IR, as shown by the GTT (P<0.001). No alterations were observed in the animals’ weight gain and in the dry/wet weight ratio of soleus and EDL muscles between groups. However, it was found a significant reduction of CSA and total GLUT4 content (P<0.05) in soleus muscle of the HMβ-treated rats.

Conclusion: The chronic administration of HMβ induces an apparent IR state in a stage in which the hyperinsulinemia seemed to account for normoglycemia. However the reduction of GLUT4 content and CSA in soleus muscle strongly indicates that the repercussions of the IR state are taking place, which might limit the recognized beneficial effects of HMβ, at least in rats under normal conditions.