Reduced insulin secretion and glucose intolerance are involved in the fasting susceptibility of common vampire bats

► Reduced insulinemia and insulin secretion impairment in Desmodus rotundus. ► Irregular and small pancreatic islets, with reduced β-cell mass, showed through morphometrical analyses. ► Glucose-stimulated insulin secretion impairment, although preserved leucine response. ► Inability to handle glucose overload by vampire bats, indicating glucose intolerance.