To determine the role of glucagon action in the metabolic phenotype of untreated insulin deficiency.

We compared pertinent clinical and metabolic parameters in glucagon receptor-null (Gcgr^−/−) mice and wild-type (Gcgr^+/+) controls after equivalent destruction of β-cells. We used a double dose of streptozotocin to maximize β-cell destruction.

Gcgr^+/+ mice became hyperglycemic (>500 mg/dL), hyperketonemic, polyuric, and cachectic and had to be killed after 6 weeks. Despite comparable β-cell destruction in Gcgr^−/− mice, none of the foregoing clinical or laboratory manifestations of diabetes appeared. There was marked α-cell hyperplasia and hyperglucagonemia (∼1,200 pg/mL), but hepatic phosphorylated cAMP response element binding protein and phosphoenolpyruvate carboxykinase mRNA were profoundly reduced compared with Gcgr^+/+ mice with diabetes—evidence that glucagon action had been effectively blocked. Fasting glucose levels and oral and intraperitoneal glucose tolerance tests were normal. Both fasting and nonfasting free fatty acid levels and nonfasting β-hydroxy butyrate levels were lower.

We conclude that blocking glucagon action prevents the deadly metabolic and clinical derangements of type 1 diabetic mice.