Page 126 - Clinical Small Animal Internal Medicine

94 Section 2 Endocrine Disease

Table 12.1 Effects of insulin and counterregulatory hormones History and Clinical Signs
VetBooks.ir Hormone Effect on carbohydrates Diabetes is characterized by hyperglycemia resulting
on carbohydrate metabolism

from insufficient insulin production or function.
Hyperglycemia causes the hallmark clinical signs of
Cortisol Increases blood glucose polyuria, polydipsia, polyphagia, and weight loss
● ↓ Glucose uptake by cells that distinguish diabetes. Some dogs and up to 50%
● ↑ Gluconeogenesis of cats present with decreased appetite. Other clinical
● ↑ Glycogenolysis signs include hepatomegaly, lethargy, cataract for-
● Inhibits insulin
mation (dogs), and diabetic neuropathy (mainly cats).
Glucagon Increases blood glucose Signs are usually slowly progressive over weeks
● ↑ Gluconeogenesis to months.
● ↑ Glycogenolysis
● Inhibits insulin
Epinephrine Increases blood glucose Polyuria and Polydipsia
● ↑ Gluconeogenesis
● ↑ Glycogenolysis Relative or absolute insulin deficiency in diabetes causes
Growth hormone Increases blood glucose reduced blood glucose uptake by liver, muscle, and adi-
● ↓ Glucose uptake by cells pose tissues, and unchecked glucose production in the
● ↑ Gluconeogenesis liver, which result in hyperglycemia. In the glomerulus of
Insulin Decreases blood glucose the kidney, nearly all the blood glucose is passively fil-
● ↑ Glucose uptake by all cells except liver, tered into the ultrafiltrate. In the proximal tubule of the
brain, red blood cells kidney, receptors are capable of resorbing only a fixed
● ↑ Glycogen formation amount of glucose from the ultrafiltrate. This fixed
● ↓ Gluconeogenesis, glycogenolysis amount is called the renal threshold, and is approxi-
mately 200 mg/dL in dogs and 250–290 mg/dL in cats.
When the amount of glucose in the blood exceeds this
Epidemiology renal threshold, glucose remains in the ultrafiltrate,
acting as an osmotic diuretic and causing polyuria and
compensatory polydipsia.
Diabetes mellitus is the most common disorder of
the endocrine pancreas in dogs and cats. The incidence
in dogs is approximately 0.13%, and the incidence in Polyphagia
cats is approximately 0.5%, depending on the study pop-
ulation, and is influenced by geographical location and Animals with uncomplicated diabetes mellitus may have
type of veterinary practice (referral or primary an increased appetite. This is governed by central mech-
accession). anisms, including increased hunger triggered by nutrient
loss (predominantly glucose), and lack of insulin‐medi-
ated uptake of glucose into cells of the satiety center,
Signalment which normally inhibits hunger.

Diabetes mellitus is a disease of middle‐aged to older Weight Change
companion animals, with peak prevalence of 7–12 years
of age in dogs and 10–13 years in cats. Intact female dogs Obesity is a common co‐morbidity in middle‐aged
and male cats are predisposed. Various breeds of cat and and senior diabetic dogs and cats. It reduces insulin
dog are overrepresented, and predisposed breeds vary sensitivity, and when superimposed on beta‐cell loss
with geographic area. For example, in the USA, dog from any cause, will hasten onset of hyperglycemia
breeds at increased risk include miniature schnauzer, and clinical signs. However, untreated diabetes melli-
Samoyed, and miniature poodle, whereas in the UK, in tus leads to weight loss, due to malassimilation of
addition to miniature schnauzer and Samoyed, breeds nutrients absorbed from the gut, and urinary loss
more commonly seen include Tibetan, cairn, border and of glucose and amino acids. Dogs in which pancreatitis
Yorkshire terriers and Labrador retrievers. In cats, is either a complicating co‐morbidity or a cause of
Burmese are overrepresented in Australia, New Zealand their diabetes may later progress to exocrine pancre-
and the UK, and in the USA, Maine Coon, domestic atic insufficiency (EPI), which exacerbates weight
longhair, Russian blue and Siamese. Norwegian forest loss, and may be first evident as increased frequency
cats and Burmese are at increased risk in Scandinavia. of defecation.