Enables glucagon receptor binding activity. Acts upstream of or within response to starvation. Predicted to be located in extracellular region. Predicted to be active in extracellular space. Is expressed in endocrine pancreas; intestine; and pancreas. Human ortholog(s) of this gene implicated in obesity and type 2 diabetes mellitus. Orthologous to human GIP (gastric inhibitory polypeptide).