A role for adrenergic receptors in the activation of intracellular signalling pathways that lead to mitogenic responses has been described [18,23,24], whilst abnormalities of sympathetic effects, including disturbances of leptin and β3-adrenergic receptor signalling may contribute to the development of obesity and type 2 diabetes in rodents [25]. Here, LEP is linked to obesity due to melanocortin 4 receptor deficiency.