Significant decrements in the expression of Ucp1 and Pgc1a mRNA as well as UCP1 protein levels induced by prolactin but not by HFD, indicate that prolactin, independently of the diet or obesity, may predispose to the development of an obese phenotype by lowering the thermogenic capacity of BAT. Here, PRL is linked to obesity due to melanocortin 4 receptor deficiency.