The melanocortin system consists of five seven-transmembrane spanning G-protein coupled receptors, MC1-MC5. Among the five members of the melanocortin receptor family, MC2 and MC5 are expressed in peripheral tissues. The MC2 receptor (ACTH receptor) is almost exclusively expressed in the adrenal cortex whereas MC5 is expressed in several organs including the adrenal cortex. Studies have shown that targeted disruption of the MC5R gene produced mice with a severe defect in water repulsion and thermoregulation caused by decreased production of sebaceous lipids. In addition, MC5 is required for secretion from several exocrine glands, indicating that melanocortin peptides integrate the function of exocrine glands.