Ovariectomized Highly Fit Rats Are Protected against Diet-Induced Insulin Resistance

Introduction: In the absence of exercise training, rats selectively bred for high intrinsic aerobic capacity (high-capacity running (HCR)) are protected against ovariectomy (OVX)-induced insulin resistance (IR) and obesity compared with those bred for low intrinsic aerobic capacity (low-capacity running (LCR)). Purpose: This study determined whether OVX HCR rats remain protected with exposure to high-fat diet (HFD) compared with OVX LCR rats. Methods: Female HCR and LCR rats (n = 36; age, 27–33 wk) underwent OVX and were randomized to a standard chow diet (NC, 5% kcal fat) or HFD (45% kcal fat) ad libitum for 11 wk. Total energy expenditure, resting energy expenditure, spontaneous physical activity (SPA), and glucose tolerance were assessed midway, whereas fasting circulating metabolic markers, body composition, adipose tissue distribution, and skeletal muscle adenosine monophosphate-activated protein kinase (AMPK), and mitochondrial markers were assessed at sacrifice. Results: Both HCR and LCR rats experienced HFD-induced increases in total and visceral adiposity after OVX. Despite similar gains in adiposity, HCR rats were protected from HFD-induced IR and reduced total energy expenditure observed in LCR rats (P

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