NOS3 and obesity due to melanocortin 4 receptor deficiency: Mice lacking endothelial NO synthase (eNOS), a key source of NO in vivo, are insulin resistant, have impaired fatty acid oxidation and display exaggerated high fat diet (HFD)-induced weight gain (Shankar et al., 2000; Duplain et al., 2001; Cook et al., 2003), and, the abundance of eNOS is remarkably diminished in obesity and diabetes (Valerio et al., 2006; Perez-Matute et al., 2009; Georgescu et al., 2011; Kraus et al., 2012; Sansbury et al., 2012).