Earl Sutherland

Cyclic AMP (cAMP) is a small molecule inside cells that acts as a 'second messenger,' relaying the signal of a hormone from the cell surface to the cell's interior. Sutherland discovered cAMP in the late 1950s while studying how the hormone epinephrine (adrenaline) triggers the liver to release glucose, showing that cAMP is the intracellular intermediary that transmits the hormone's signal.

A second messenger is a molecule produced inside a cell in response to a 'first messenger' such as a hormone binding to a receptor on the cell surface. Sutherland's concept explained how hormones like epinephrine and glucagon, which cannot enter cells, can still trigger dramatic internal changes—like the breakdown of glycogen into glucose—by generating cAMP as their internal relay signal.

Sutherland was awarded the 1971 Nobel Prize in Physiology or Medicine for his discoveries concerning the mechanisms of action of hormones, specifically the identification of cyclic AMP as a second messenger. He conducted the foundational research at Case Western Reserve University (then Western Reserve University) in Cleveland, Ohio.

Sutherland's discovery that cAMP mediates hormone action inside cells opened up the entire field of receptor signaling and second-messenger biology, which became central to pharmacology. Many widely used drugs, including beta-blockers for heart conditions and bronchodilators for asthma, work by targeting receptors that signal through the cAMP pathway that Sutherland elucidated.