INS and obesity due to melanocortin 4 receptor deficiency: Chronic melatonin administration given from the onset of the obesity-inducing diet was recently shown to prevent the harmful effects of obesity, such as insulin resistance and dyslipidaemia and to protect the hearts of obese rats against myocardial ischaemia–reperfusion injury.32 In addition, we observed that short-term melatonin consumption also reduced systemic insulin resistance and conferred cardioprotection.33 However, whether melatonin treatment affects myocardial insulin sensitivity and glucose uptake remains unknown.