Diabetes mellitus
Diabetes mellitus is a metabolic disorder of carbohydrates, proteins and fats due to deficiency of insulin and with insulin resistance. It is observed in dogs, humans and cats.
Diabetes mellitus can be classified into three types –
- Type I (Insulin-dependent diabetes mellitus – IDDM)
- Type II (Non-insulin dependent diabetes mellitus – NIDDM)
- Impaired glucose tolerance (IGT)
Type I diabetes mellitus is characterized by loss of beta cells leading to insulin deficiency.
Type II diabetes is characterized by insulin resistance which may occur along with reduced insulin secretion. Type 2 diabetes is the most common type.
Diabetes mellitus is characterized by persistent hyperglycemia
A fasting blood glucose level of 125mg/dl or more is suggestive of diabetes mellitus.
Insulin deficiency affects entire metabolism of the organism: fat, protein, carbohydrate, electrolyte and water. It leads to the inability of peripheral tissues to use glucose for energy or for glycogen synthesis, whereas it stimulates glycogenolysis and gluconeogenesis which results in hyperglycemia.
Glucose appears in urine (glucosuria) and causes osmodiuresis leading to water and electrolyte loss, polyuria, dehydration and hemoconcentration. Other signs include polyphagia, polydipsia, and hypercholestrolemia.
Insulin deficiency activates hormone-sensitive lipase activity leading to increased fatty acid mobilization for oxidation and energy, increased acetyl‑CoA formation which on conversion to ketone bodies causes ketonemia and ketonuria.
Protein catabolism is enhanced in insulin deficiency and amino acids are used for gluconeogenesis. There is a negative nitrogen balance with weight loss. BUN is elevated in dogs.
Pituitary diabetes is weakly sensitive to insulin whereas adrenal diabetes is moderately insulin sensitive and pancreatic diabetes is highly sensitive to insulin.
When plasma glucose is elevated for a long time, small amounts of Hb are non-enzymatically glycosylated to form HbA1c. Controlling the diabetes with insulin reduces this level; HbA1c concentration is measured clinically as an index of diabetic control for the 4-6 week period before the measurement. Higher level will be observed in poorly controlled diabetes.