SHOULD WE FEAR CHOLESTEROL IN EXCESS
IN CATS AND DOGS ?
Nature and roles of cholesterol
The cholesterol is a lipidic molecule, indispensable to the body because:
- it is one of the main components of the cellular membranes,
- it is a precursor of steroid hormones (oestrogens, androgens…), and biliary salts.
Cholesterol is synthetized by the liver, but some also comes from the animal fats of the diet.
Transport of cholesterol in the blood
There is always a flow of cholesterol in the blood, to satisfy the requirements of the different organs. Because of its lipidic structure that makes it insoluble, it is carried along inside large molecules, the lipoproteins, that are soluble in the blood. There are 4 main types of lipoproteins, synthetized by the intestinal cells and/or by the liver. They are classified according their respective density. (The higher the density is, the less lipids they contain).
- chylomicrons: exclusively produced by the small intestine cells after a meal. They go through the lymphatic vessels before reaching the general circulation. Their major role is to transport dietary triglycerides up to the liver.
- VLDL (Very Low Density Lipoproteins): they are mainly in charge to dispatch the triglycerides synthetized in the liver to the different organs of the body.
- LDL (Low Density Lipoproteins): these are VLDL, once they have “ delivered ” their triglycerides. Then they supply the hepatic cholesterol to the organs and tissues. It is commonly called the “ bad cholesterol ” .
- HDL (High Density Lipoproteins : compared to LDL, they have an opposite role. They collect cholesterol in excess throughout the body, and bring it back to the liver that will store, redispatch or eliminate it through the bile. Here we speak about “ good cholesterol ”.
Cholesterol is then mostly carried along by LDL and HDL. In man, the most important lipoproteins are LDL. These are the ones that can cause fat deposits inside the arteria (atheroma), and be at the origin of so common diseases in man: coronary diseases, myocardial infarction… On the contrary, in dogs and cats, there are twice as much HDL than LDL, and 80 % of the total cholesterol is binded to HDL. Here, the “ good cholesterol ” is the most important. This physiological difference could explain why atheromatosis is so rare in these species.
Disorders of the lipidic metabolism
The fact that cholesterol does not deposit in the vascular system does not mean that there is no possible disorder in the lipidic metabolism of cats and dogs.
When there is a global excess of lipids in the blood, one speaks about hyperlipemia. In that case, the serum is cloudy, with a “ strawberry milk ” colour. After sedimentation during one night, a white “ creamy ” appears on the surface. A clear serum does not mean however that everything is normal. When there is only an excess of cholesterol in the blood, there is no modification of the serum visible. Only the dosage of cholesterol and triglycerides (after 12 hours fasting), can confirm hyperlipemia.
Reference normal values
Total cholesterol (g/l) 0,8 à 2,8 0,4 à 1,7
Triglycerides (g/l) 0,3 à 1,5 0,2 à 1,1
Those troubles of the lipidic metabolism are scarcely observed alone. Only a few cases are known: in miniature Schnauzer and in cats. In general, it is rather the consequence of another disbalance, mostly from hormonal origin.
- 70 % of hypothyroidism cases induce an abnormal rise in blood cholesterol;
- Dysfonctionment of surrenal glands (hypercorticism)
- Diabetes, acute pancreatitis
- Renal deficiency
- Drug intoxication: steroid anti-inflammatory drugs, contraceptive hormones…
- Hepatic deficiency (fat storage in excess in cats): hypercholesterolemia can be one the first signs of an hepatic disorder. It should not be neglected.
- In obese animals, such as obese cats that suddenly stop eating, one can notice an elevation of blood cholesterol and triglycerides, but it is not a constant phenomenon.
When faced with triglycerides or cholesterol in excess in the blood, the veterinarian must look for the primary cause of the dysbalance, and treat it first. On a dietetic aspect, the dietary fats have to be drastically restricted. However, the supply of essential fatty acids must not be forgotten.
Increasing the fiber content of the diet is also advised. Fibers adsorb biliary salts and prevent from the recycling of cholesterol contained in these salts.
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