Today's Veterinary Practice

MAR-APR 2018

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ESSENTIALS 17 MARCH/APRIL 2018 ‚óŹ TVPJOURNAL.COM ESSENTIALS The term dysrexia refers to a disruption in food intake, including anorexia (not eating), hyporexia (eating less) and eating an unbalanced diet (eg, the patient that will eat roast beef but not a prescribed low- protein diet). Although a short period of inadequate intake (1 or 2 days) is generally well tolerated, longer periods of hyporexia may slow recovery and put patients at risk of other complications. These include changes in the gastrointestinal (GI) microbiome (ie, dysbiosis), delayed gastric emptying and intestinal hypomotility, and compromise to enterocyte health and mucosal integrity. Hyporexia and anorexia are known to predispose vulnerable patients to translocation of potential pathogens from the GI tract. Cats, particularly those with a robust body condition score (BCS), will begin to accumulate fat within their hepatocytes after just a few days of anorexia, with overt compromise due to hepatic lipidosis noted within 10-14 days. In addition to all the physiological consequences of poor food intake, this takes a toll on the pet owner and can lead to premature decisions about discontinuation of therapy or euthanasia. Owners are often disinclined or unable to administer oral medications if the pet is not eating. The mechanisms by which illness suppresses appetite are complex, and we do not yet have a clear picture of them all. Changes in messaging within the hypothalamus likely play a key role, with a disturbance of the usual signals regarding satiety. In healthy animals, two distinct neuronal populations regulate this process, with one set (the orexigenic neurons) driving food-seeking behaviors, while the other (the anorexigenic neurons) depress appetite. Activity within these centers also impacts metabolic rate, so that energy stores are conserved when food is scarce. Some diseases, primarily those associated with inflammation, can essentially hijack the anorexigenic neurons, so that appetite is suppressed but the metabolic rate is concurrently increased. This is one of the pathways behind the cachexic conditions, in which weight loss can occur alarmingly quickly, and at a much faster rate than we would expect simply from a lack of intake. Cachexia is sometimes referred to as "protein- energy wasting syndrome," a phrase that effectively captures the underlying metabolic derangement. There are several neuroendocrine systems that drive satiety and satiation, but only one hormone specifically drives hunger, ghrelin, which is produced primarily in the stomach. Ghrelin is essential for survival, as it is the primary trigger for activity in the orexigenic (food seeking/hunger) center within the hypothalamus. Other hormones, such as cortisol and thyroxine, may also support food-seeking behaviors, but have other more complex metabolic effects. shutterstock.com/Lightspruch Dealing With Dysrexia Audrey K. Cook, BVM&S, DACVIM, DECVIM, DABVP (Feline) College of Veterinary Medicine and Biomedical Sciences Texas A & M University NUTRITION

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