In the normal dog fasting does not usually result in hypoglyceraia. Therefore a serum glucose concentration < 60 mg/dl is almost always due to either organic disease or to laboratory error. In an animal with normal glucose homeostasis, insulin secretion is stimulated when the blood glucose is > 110 mg/dl; insulin secretion is depressed and secretion of hormones that oppose insulin (epinephrine, glucagon, cortisol, growth hormone) is stimulated when the blood glucose falls below < 60 mg/dl. Insulin acts by decreasing the rate of glycogenolysis and gluconeogenesis by the liver and increasing the rate of uptake of glucose by insulin sensitive tissues. In the presence of an insulinoma, neoplastic pancreatic beta cells continue to release insulin despite the presence of hypoglycemia. Clinical signs are dependent on the degree of hypoglycemia and the rate at which it occurs.
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