Hyperlipidaemia in the dog
Hyperlipidaemia describes increased plasma concentrations of cholesterol and/or triglyceride and may arise from primary, often inherited defects in lipoprotein metabolism or appear secondary to systemic disease. The aim of this study was to characterise the abnormalities of lipoprotein metabolism responsible for hyperlipidaemia in the dog, to establish their effect upon the health of the individual, and to evaluate approaches to therapy. A combined ultracentrifugation/precipitation technique for the measurement of very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL) was adapted and validated for use with canine plasma. Alternative methods of analysis were evaluated, but none of the commercially available precipitation reagents for the measurement of human lipoproteins were found to be suitable for use in the dog. Lipoprotein electrophoresis was useful in the investigation of hyperlipidaemic patients by allowing the identification of other lipoprotein classes, namely chylomicrons, HDL1 and B-VLDL. The effects of age, breed, sex and health status on lipoprotein concentrations in the dog were established. The HDL concentration was greater in entire females than males and certain disease processes were found to displaycharacteristic lipoprotein abnormalities. Dogs with diabetes mellitus and hypothyroidism presented with defects in the metabolism of LDL and HDL and triglyceride-rich lipoproteins, while hyperadrenocorticism, obstructive jaundice and protein-losing nephropathies were predominantly associated with abnormalities of cholesterol metabolism. A decreased lipoprotein lipase activity was partially responsible for the hyperlipidaemia in hypothyroid dogs. Overt hyperlipidaemia was not identified in obese dogs, but aberrations of triglyceride metabolism were identified by kinetic analysis and found to be a result of decreased lipoprotein lipase activity. Impaired triglyceride clearance in the postprandial period may therefore predispose obese dogs to the development of acute pancreatitis.