LEP and obesity due to melanocortin 4 receptor deficiency: To determine the potential involvement of leptin signaling in obesity and/orage-induced effects on cardiomyocyte contractile function, intracellularCa2+ homeostasis and O2−production, we evaluated the leptin receptor Ob-R, the post-leptin receptorsignaling molecule STAT-3 and STAT-3 phosphorylation.