Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous peptide that stimulates cAMP production in the anterior pituitary. PACAP and PACAP-related peptide (PRP) regulate immune function and display increases in expression when hosts are challenged with bacterial pathogens. PACAP and PRP also control expression of reproductive hormones such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Additionally, PACAP and PRP bind the PAC1 receptor and VPAC1/2 receptors. PACAP itself inhibits K+ amplitude of delayed rectifier K+ channels, exhibiting anti-apoptotic activity in cerebellar granule cells.