• Glucose in the blood is derived from three main sources:

• The plasma concentration of glucose is controlled by a number of hormones, in particular, insulin and glucagon. The physiology of glucose homeostasis is controlled primarily by insulin release in response to elevated glucose levels (postprandial), although in birds, glucagon appears to serve as the primary regulator. Significant species variations in glucose levels have been noted. In general, levels are lowest in reptiles (60 to 100 mg/dL) and highest in birds (200 to 500 mg/dL), with mammals in between (100 to 200 mg/dL).

Glucose that is not needed for energy is stored in the form of glycogen as a source of potential energy, readily available when needed. Most glycogen is stored in the liver and in muscle cells. When these and other body cells are saturated with glycogen, excess glucose is converted to fat and is stored as adipose tissue.

Clinical Applications

Causes of Abnormally High Levels

• Hyperglycemia

• Catecholamine release

• Increased growth hormone (growth hormone–producing tumor)

• Increased glucagon (glucagon-producing tumor)

• Increased progesterone production (diestrus in female)

• Pancreatitis

• Drugs (see later)

• Hyperthyroidism

• Moribund animals

• Birds

image Hyperglycemia is generally defined by blood glucose concentrations exceeding 500 mg/dL.

image Hyperglycemia most often results from catecholamine release from stress, glucocorticosteroid excess from administration of corticosteroids, and diabetes mellitus.

image Exertion, excitement, and extreme temperatures stimulate the release of catecholamines, resulting in a mild to moderate increase in the blood glucose concentration. Stress hyperglycemia can occasionally produce a strong positive on urine glucose dipstick, similar to diabetes mellitus.

image Excess glucocorticosteroids normally cause a mild to moderate increase in the blood glucose concentration (≤600 mg/dL) in birds.

image Concentrations greater than 700 mg/dL are suggestive of diabetes mellitus in birds.

image The pathophysiology of diabetes mellitus in birds is variable, however, and appears to be associated with excess glucagon in the presence of hyperglycemia. In psittacine birds, pancreatitis and pancreatic islet cell tumors are known causes. In some species (e.g., tucans [Ramphastidae]), diabetes occurs commonly and may be related to diets rich in fruits. Budgerigars and cockatiels are predisposed to diabetes associated with hepatic lipidosis. Birds suffering from diabetes mellitus demonstrate polyuria and urinary glucose concentrations exceeding 1 mg/dL.

image Reproductively active cockatiel hens can present with “pseudodiabetes.” Plasma glucose levels are elevated but remain under 1000 mg/dL. The cause appears to be reduced pancreatic function from inflammation associated with yolk peritonitis.

• Reptiles

• Ferrets

• Rabbits

image Hyperglycemia is a relatively common finding in rabbits and can be accompanied by glycosuria.

image Stress-induced catecholamine release is believed to be the most common cause. Handling pet rabbits or warm temperatures result in increased blood glucose.

image Glucocorticoid excess (e.g., stress induced, exogenous corticoids, hyperadrenocorticism) is also possible.

image Hyperglycemia is associated with severe gastrointestinal distress ranging from acute obstruction to chronic stasis.

image Diabetes mellitus is rarely a cause of hyperglycemia in rabbits and is rarely diagnosed in pet rabbits. Rare hereditary diabetes occurs in some populations. Herbivorous animals withstand the absence of insulin more readily than carnivorous ones. Management of hyperglycemia in herbivorous animals is done via diet modification.

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Jul 29, 2016 | Posted by in EXOTIC, WILD, ZOO | Comments Off on Glucose

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