High-fat feeding reduced muscle uncoupling protein 3 expression in rats

Uncoupling Protein 3 (UCP3), largely expressed in skeletal muscle, is modul ated by cold, thyroid hormones, leptin, fasting-refeeding and exercise trai ning among other factors in a tissue-specific manner. In brown adipose tiss ue, there is an increase in UCP3 levels after high-fat feeding and beta(3)- adrenergic agonist treatment. Controversial effects of these agents have be en reported in skeletal muscle. The aim of this experimental trial was to e valuate the effect of high-fat feeding and beta(3)-adrenergic agent treatme nt on skeletal muscle UCP3 expression levels. I,ean rats were fed a cafeter ia diet for 30 days and found to have significantly higher fat stores and b ody weight than control rats at the end of the experimental period. When ca feteria-diet rats were daily i.p. injected with Tertatolol for 30 days; a d ecrease in total fat mass and body weight was found. Such an effect was not observed in fa/fa rats. Interestingly, gastrocnemius muscle UCP3 mRNA leve ls were significantly reduced in cafeteria-diet rats when compared to lean animals. Likewise, mitochondrial O-2 consumption in gastrocnemius muscle wa s also significantly decreased (-31 %) in cafeteria-diet rats as compared t o the control group. It is suggested that the down-regulation of UCP3 gene expression together with the lower O-2 consumption observed in high fat fed rats may be linked to lower fatty oxidation, which would promote triglycer ide accumulation.