Veterinary Physiology-III

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 – noninsulin-dependent diabetes mellitus – (NIDDM) and 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.