Cholesterol, in dogs as well as humans, is the most common steroid. Dogs naturally produce cholesterol in their livers and other organs, and get it from their food. The cholesterol in a dog's blood occurs as low-density (LDL) and high-density (HDL) lipoproteins. All dogs experience raised cholesterol levels for up 10 hours after eating as lipoproteins transport the fats in their food through their blood vessels. Dogs, however, can have chronically elevated cholesterol levels for a variety of reasons.
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Heredity
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A 1992 study at the University of London's Royal College of Veterinary Medicine found that a family of otherwise healthy briards had elevated cholesterol levels. Because they had none of the diseases, such as diabetes mellitus, normally linked to secondary high cholesterol, the researchers concluded that the briard breed may have a genetic abnormality.
Cornell University's Animal Health Diagnostic Center says that hereditary hypercholesterolemia (high blood cholesterol) has been found in Doberman pinschers, Shetland sheepdogs and rottweilers.
Diabetes Mellitus
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A dog's pancreas normally produces the enzyme lipase, which helps metabolize dietary fats. With diabetes mellitus, a dog doesn't release enough insulin to stimulate normal lipase production, causing elevated levels of cholesterol. Breeds susceptible to diabetes mellitus are poodle, beagle, miniature schnauzer and pinscher, Cairn terrier, dachshund, keeshond and puli.
Hyperadrenocorticism and Hypothyroidism
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Breeds at risk of high cholesterol from hyperadrenocorticism include terrier, Labrador retriever, beagle, German shepherd, poodle and dachshund. The adrenal glands of dogs with hypradrenocorticism produce excessive amounts of corticosteroids. These hormones increase the dog's lipase production to levels that raise cholesterol by releasing stored fat into the bloodstream.
Dogs with hypothyroidism aren't producing enough T3 hormone. T3 stimulates the liver's LDL cholesterol receptors, which scrub LDL from the blood. A lack of T3 hormone means a higher LDL level.
Nephrotic Syndrome
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Nephrotic syndrome is a kidney disorder that raises both HDL and LDL cholesterol, although according to Cornell, exactly how it does this isn't known.
Medication
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A 1994 study at the University of Amsterdam's Department of Endocrinology found that the drug amiodarone raised rats' cholesterol levels by suppressing their T3 production. This drug is used to treat heart arrhythmia in dogs.
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