Cyclic AMP is the second messenger in signal coupling with glucagon and epinephrine to stimulate glycogen breakdown. Glucagon is a peptide hormone synthesized and secreted from α-cells of the islets of Langerhans of the pancreas. Epinephrine is a catecholamine synthesized by the adrenal medulla. Both hormones raise blood glucose as part of their effect. To signal the cell, these hormones activate adenylate cyclase, an enzyme associated with the plasma membrane, which catalyzes the conversion of ATP into Cyclic AMP. Cyclic AMP then serves as a second messanger within the cell.