The metabolic syndrome, a morbid condition well-described in humans, is defined as a set of risk factors such as obesity (mainly visceral obesity), arterial hypertension, dyslipidemia and insulin resistance; at least three of these events must occur simultaneously in the same individual for the diagnosis to be confirmed. Also known as X syndrome, or plurimetabolic syndrome or insulin resistance syndrome, is the most common metabolic disease in humans and also their main cause of cardiovascular morbid events. It is known that the binding factor among these alterations changes is insulin resistance (characterized by hyperinsulinemia). In other words, the central abnormality associated with the syndrome appears to be the resistance of peripheral tissues to insulin, in a low biological response to circulating levels of insulin. The consequences, in most cases, not only changes the carbohydrates metabolism but, mainly, changes the lipids metabolism and its anabolic action. The fundamental keys in insulin resistance are the elevation of circulating free fatty acids, from lipolysis of adipose tissue (the visceral, in particular) and the exaggerated release of adipokines such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), resistina and leptin. These elements, in the condition of obesity, interfere with the various steps of the insulin signaling, as in the substrate phosphorylation of insulin receptor (IRS) and phosphatidylinositol 3-kinase (PI-3-K).
The reduced action of insulin on lipoprotein lipase, the lower uptake of glucose and increasing release of free fatty acids and glycerol, provide an increased production of VLDL by the liver, together with the increase of triacylglycerol and reduction of HDL cholesterol, a situation that can be called as atherogenic dyslipidemia. Although a frequent phenomenon, the increase in adiposity becomes clinically relevant when the excessive accumulation of fat was associated with a pathophysiological situation, especially the conditions of hyperlipidemia (elevation of cholesterol and triacylglycerol), and consequent hyperlipoproteinemia. The lipoproteins, macromolecular aggregates whose function is the transport of lipids in the blood and lymphatic circulation, are classified into different categories according to different combinations of lipids and proteins in its composition. In dogs, four major classes of lipoproteins are well defined: chylomicrons, a lipoprotein exogenous and three classes of endogenous lipoproteins, VLDL (very low density lipoprotein), LDL (low density lipoprotein) and HDL (high density lipoprotein ). The separation of lipoproteins can be realized by various methods and depend on the size and shape, electrical charge and density.
The clinical relevance of the metabolic syndrome is related to its role in the development of cardiovascular disease and diabetes mellitus development. The diagnosis is established when we identify three or more of the named events. In dogs, the metabolic syndrome is well recognized in experimental conditions, where the obesity is induced by excessive administration of fat rich diets. The syndrome is associated with the development of atherosclerotic disease, lipodystrophy, abnormal hematological and blood coagulation. Insulin resistance resulting from obesity leads to activation of the hypothalamic-pituitary-adrenal, making affected individuals in a state of hypercortisolism. They also reduced serum levels of GH, hypogonadism and hyperandrogenism. In veterinary clinic for small animals not many publications relating the tables of canine obesity and metabolic syndrome. Actually, the presence of hyperlipidemia in client-owned obese dogs and in dogs with hypercortisolemia is associated with elevation of atherogenic lipoproteins such as VLDL and LDL. In animal studies, when compared to values of normal dogs, it was possible to note changes suggestive of all these events, such as insulin resistance and hyperlipidemia, and obesity itself. Also, some reports already show the occurrence of insulin resistance in obese dogs with spontaneous obesity, where one third of the animals studied had hyperinsulinemia, compared them to normal dogs.
We conclude that a considerable part of the obese client-owned dogs have metabolic syndrome, configured by obesity, hyperlipidemia and insulin resistance, which is a risk condition for the development of diabetes mellitus as well as atherosclerosis, morbid condition unusual for dogs but now described in the presence of endocrine or metabolic disorders.
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