LEP and obesity due to melanocortin 4 receptor deficiency: In line with endothelial dysfunction observed in patients suffering from obesity, organ bath experiments revealed an impaired endothelium-mediated vascular relaxation in isolated aortic rings of HFD-fed WT mice as well as in obese Lep−/− mice, which was not observable in obese Mpo−/− mice (Figures 2F and 2G).