Triglyceride

Triglyceride



Basic Information image



Definition


A triglyceride (TG) molecule consists of a glycerol backbone esterified with three fatty acids. Triglycerides are the main constituent of vegetable and animal fats in the diet, and are the main constituent of the body’s fat stores. Serum or plasma total TG concentrations may be determined to assess metabolic disorders.



Synonym(s)




Triacylglycerol


Triacylglyceride



Typical Normal Range (US Units; SI Units)


6 to 54 mg/dL (0.07–0.61 mmol/L). This is the typical range for full-sized horses. Healthy ponies and donkeys may have higher triglyceride levels. Healthy donkeys have been reported to have levels as high as 290 mg/dL (3.28 mmol/L).



Physiology


TGs are not soluble in the aqueous environment of the bloodstream. For transport in the blood, they are carried by macromolecular particles called lipoproteins. The surface of lipoprotein particles is made up of proteins, free cholesterol, and phospholipids, oriented so as to be water soluble, and hydrophobic substances such as TG and esterified cholesterol are carried in the cores of the particles. Chylomicrons (CM) and very low density lipoprotein (VLDL) particles are the main TG carriers among the various types of lipoproteins, whereas low-density lipoproteins (LDL) and high-density lipoproteins (HDL) are mainly involved in transport of cholesterol. The CM particles carry dietary TG from the intestine to extrahepatic tissues such as muscle and adipose tissue. The VLDL particles carry TG made in the liver to extrahepatic tissues. Various disease states increase the amount of VLDL made by the liver and/or interfere with the clearance of CM or VLDL associated TG from the blood via uptake by muscle and/or adipose tissue. During conditions favoring lipolysis, nonesterified fatty acids (NEFAs) can be released from TG in the body’s fat stores and used for energy production. Excess mobilized NEFAs beyond what can be oxidized for energy may be reesterified into TG molecules in the liver. Accumulation of excess TG in the liver results in hepatic lipidosis (fatty liver). The equine liver is efficient at forming and secreting VLDL particles so as to remove excess TG, but disorders leading to impaired extrahepatic removal of the TG from those VLDL particles leads to hypertriglyceridemia, which, at levels greater than 400 to 500 mg/dL (4.52–5.65 mmol/L), causes lipemia.



Causes of Abnormally High Levels


Conditions involving negative energy balance favor lipolysis and are likely to result in hypertriglyceridemia. Such conditions include malnutrition, anorexia, stress, pregnancy, lactation, endotoxemia, and renal failure. Ponies, donkeys, and miniature horses are predisposed to become markedly hypertriglyceridemic under such conditions. Obesity is a predisposing factor to development of hypertriglyceridemia during metabolic stress. Hypertriglyceridemia has been reported to occur within 3 days of fasting in horses. Equids with diabetes mellitus or metabolic syndrome are likely to be hypertriglyceridemic, as are those with hyperadrenocorticism (Cushing’s-like syndrome, usually due to functional pituitary adenoma or adenomatous hyperplasia). Foals in the first 2 weeks of life have triglyceride levels higher than those of adults. Transient hypertriglyceridemia occurs postprandially in some species but this possibility is not much discussed in the equine literature, except in regard to its occurrence in nursing foals.

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Triglyceride

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