Glucagon R (GCGR) is a receptor for glucagon which plays a central role in regulating the level of blood glucose by controlling the rate of hepatic glucose production and insulin secretion. The activity of GCGR is mediated by G proteins which activate adenylyl cyclase and also a phosphatidylinositol-calcium second messenger system. Defects in GCGR are a cause of non-insulin-dependent diabetes mellitus.