The TGR(mRen2)27 rat (Ren2) harbors the mouse renin gene, exhibits increased tissue angiotensin II (Ang II) levels, and develops whole body and skeletal muscle insulin resistance as well as severe hypertension. Evidence is accumulating that renin-angiotensin-aldosterone system (RAAS) mediated increases in reactive oxygen species (ROS) contribute to impaired insulin signaling in a variety of tissues. We have previously demonstrated that RAAS mediated oxidative stress contributes to skeletal muscle insulin resistance in Ren2 rats and that blocking the Ang II type I receptor (AT[sub 1]R) or scavenging superoxide improves whole body glucose tolerance and skeletal muscle insulin-stimulated glucose uptake. However, it is not known whether blocking mineralocorticoid receptors will improve insulin sensitivity in this model. Male Ren2 and Sprague-Dawley (SD) rats (age 6-8 wks) were implanted with time-release pellets containing either spironolactone (5 mg; 0.24 mg/day) or placebo subcutaneously for 21 days. This dose of spironolactone was insufficient to affect blood pressure. After treatment, 2-deoxyglucose transport was measured in isolated soleus strips and epitrochlearis muscles incubated in the presence or absence of a maximally effective dose of insulin (100 nM). ROS production was determined by measuring photon emission from soleus muscle samples in the presence of lucigenin (5 µM) and NADPH (100 µM). Data confirm that ROS production was significantly higher in soleus muscles (190%) from Ren2 compared to SD rats. Spironolactone treatment prevented the increase in ROS production in soleus muscles. Furthermore, insulin stimulated glucose transport was lower in soleus (28%) and epitrochlearis (50%) muscles from Ren2 compared to SD rats. Spironolactone treatment of Ren2 significantly improved insulin stimulated 2-deoxyglucose transport in soleus muscles (115%) compared to muscle from placebo treated rats. Similar improvements were observed in epitrochlearis muscles. Collectively, these findings suggest that mineralocorticoid receptor activation contributes to the increase in ROS and decrease in insulin stimulated glucose transport observed in the skeletal muscles of Ren2 rats. [ABSTRACT FROM AUTHOR]