The effect of peroxisome proliferator-activated receptor (PPAR)-alpha activators on the liver is well established, but the other effects on muscle and adipose tissue about lipid metabolism and insulin sensitivity are not clear. We investigated whether PPAR-alpha activation affects adiposity of skeletal muscle as well as adipose tissue and improves insulin sensitivity in spontaneous type 2 diabetes model, Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Thirty-three weeks of aged, 20 male OLETF rats were divided into two groups. Control group (n = 10) was fed with chow and treatment group (n = 10) with chow contained fenofibrate for 7 weeks. At the age of 40 weeks, all rats were examined with MRL intravenous glucose tolerance test, and then sacrificed for measurement of fat mass and RNA analyses. The total fat (the sum of subcutaneous, mesenteric, epididymal. and retroperitoneal fat pads) measured by dissection was significantly reduced in treatment group. The signal intensity of muscular adiposity was significantly decreased in treatment group. The mRNA levels of FAT/CD36 and mitochondrial carnitine palmitoyltransferase I (M-CPTI) in liver were remarkably increased. Fasting plasma insulin and leptin levels, insulin response after intrallenous glucose loading and homeostasis model assessment insulin resistance (HOMA(IR)) index were lowered in treatment group. Fenofibrate increase mitochondrial fatty acid beta-oxidation in liver but not in skeletal muscle and lower the plasma levels of triglyceride and free fatty acid. It might result in reduction of adiposity of truncal adipose tissue and skeletal muscle. We suggest that reduction of adiposity in trunk and skeletal muscle might improve insulin sensitivity, (C) 2002 Elsevier Science (USA). All rights reserved.