Veterinary Medicine - September 2007 - (Page 589)

ESSENTIAL ELEMENT The disease Hyperlipidemia involves hypertriglyceridemia, hypercholesterolemia, or both. It can be primary (genetic or idiopathic) or secondary to other diseases such as hypothyroidism, pancreatitis, hyperadrenocorticism, or diabetes mellitus. lial cells of muscle and adipose tissue, is activated and hydrolyzes the triglyceride of chylomicrons to fatty acids and glycerol within six to 10 hours.3,4,7 The activity of lipoprotein lipase is enhanced by heparin, insulin, and thyroid hormone.3,9 The free fatty acids diffuse into cells and are either resynthesized to triglycerides and stored in adipocytes or used for energy in myocytes and other cells.7 The remnants of the chylomicrons remain in the plasma and are removed by the liver.3,4,7 Fatty acids in the remnant chylomicrons and those endogenously mobilized from adipocytes are removed by the liver, resynthesized into triglycerides, and packaged into VLDL particles.3,7 Adipocytes mobilize fatty acids for release into the plasma by activating intracellular hormone-sensitive lipase.3,7 Hormones that stimulate this lipase include epinephrine, norepinephrine, ACTH, corticosteroids, growth hormone, and thyroid hormone.3 An increased ratio of glucagonto-insulin activity also stimulates fatty acid mobilization.3 VLDLs are important triglyceride transporters during fasting.7 In plasma, endothelial lipoprotein lipase splits the VLDL molecules into free fatty acids plus glycerol.3,4,7 The fatty acids of the VLDLs are removed via lipoprotein lipase.7 As the VLDLs lose fatty acids, their density increases and VLDLs become LDLs.7 LDL is VLDL minus triglyceride. LDLs are rich in cholesterol and phospholipids, and their major function is to transport cholesterol to tissues.4,7 Cholesterol is an important component of cell membranes and hormone synthesis.4,7 Excess LDLs eventually bind to LDL receptors on hepatocytes and are removed from the plasma.7 HDL is the smallest and highest density lipoprotein.4 It is synthesized and secreted from both the liver and intestine.7 HDL comprises most of the cholesterol in dogs and cats. It serves as a reverse cholesterol transporter and scavenges excess cholesterol from cells, returning it to the liver for excretion into the bile.4 Increased risk of cardiovascular disease is associated with increased LDL and insufficient HDL concentrations in people. In people, LDL is considered the bad TABLE 1 Major Lipoproteins and Characteristics* Class VLDL LDL HDL Density (g/ml) 0.093–1.006 1.019–1.087 (dogs) 1.030–1.043 (cats) 1.063–1.21 Diameter (nm) Major Lipid Class 75–1,200 30–80 18–25 7.5–20 Dietary triglycerides Endogenous triglycerides Cholesterol esters Cholesterol esters, phospholipids Chylomicron < 0.96 *Source: Ganong WF. Energy balance, metabolism, and nutrition. In: Review of medical physiology. 20th ed. New York: 2001;271306; Mayes PA. Lipid transport and storage. In: Harper’s biochemistry. 24th ed. Stamford, Conn: 1996;254-269; and Bauer JE. Lipoprotein-mediated transport of dietary and synthesized lipids and lipid abnormalities of dogs and cats. J Am Vet Med Assoc 2004;224:668-675. VETERINARY MEDICINE September 2007 589

Table of Contents Feed for the Digital Edition of Veterinary Medicine - September 2007

Contents Letters Leading Off The Veterinary Medicine Interview: Dr. William J. Kay Idea Exchange Practical Matters Salivary Mucoceles in Cates: A Retropspective Study of Seven Cases Hyperlipidemia in Dogs and Cats Purina Insert The Latest Management Recommendations for Cats and Dogs with Nonketotic Diabetes Mellitus CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - September 2007

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