- Equine metabolic syndrome
Also known as Peripheral Cushings Disease and Equine Syndrome X
This is an area of much new research and is increasingly believed to have a major role in conditions such as
laminitis . Although many factors (includingcortisol metabolism andadipocyte (fat cell) turnover) are involved, the primary cause isinsulin resistance . This is similar totype II diabetes in humans, where the action ofinsulin is impaired, despite often elevated concentrations.Ponies and horse breeds that evolved in relatively harsh environments with only sparse grass (such as domesticated Spanish Mustangs and Peruvian Pasos, among others), [cite news |first=L |last=Gray |authorlink= |coauthors= |title=Equine Metabolic Syndrome Versus Cushing's Syndrome |url=http://www.thehorse.com/viewarticle.aspx?ID=8963 |publisher=The Horse |year=2007 |month=2 |day=19 |accessdate=2008-06-01 ] tend to be more prone to EMS and insulin resistance, possibly as a survival mechanism (i.e. lay down fat when conditions are good). Such animals are sometimes called "
easy keeper s."Pathogenesis
In EMS, peripheral adipocytes (fat cells) synthesise
adipokines which are analogous to cortisol, resulting inCushings syndrome -like symptoms. cite journal | last =Johnson | first =PJ | coauthors =Messer T, Kellon E | year =2004 |title =Treatment of Equine Metabolic Syndrome | journal =Horse Industry of Alberta Proceedings| | url =http://www.albertahorseindustry.ca/hboc/2004/proceedings/laminitis.pdf | accessdate = 2008-05-31] However,cortisol levels are grossly normal, cite journal | last = | first = | coauthors = | year = | month = | title =Equine Metabolic Syndrome | journal =Proceedings of the Minnesota Veterinary Medical Association | url =http://www.mvma.org/Proceedings/Equine/Equine3.htm | accessdate = 2008-05-31] and there is nopituitary dysfunction.In addition, omental adipocytes may produce the enzyme11β-hydroxysteroid dehydrogenase type 1 , which "regenerates" activecortisol from its inactive metabolite,cortisone , which may induce a form of Cushings whereby normal cortisol levels have an exaggerated action due to a longer systemicHalf-life .In addition, a hormone termed
resistin has been shown to be produced in adipose tissue, which is a known cause for insulin resistance.EMS is also implicated in the development of
laminitis ; [ cite journal | last =Treiber | first =KH | coauthors =Kronfeld DS, Geor RJ| year =2006 | title =Insulin Resistance in Equids: Possible Role in Laminitis | journal =The American Society for Nutrition | volume =136 | pages =p. 2094S-2098S | url =http://jn.nutrition.org/cgi/content/full/136/7/2094S | accessdate = 2008-05-31 | quote = ] however, recent research suggests that the situation is more complex, in that "compensated insulin resistance is essentially physiological and health sustaining", and only when this compensatory mechanism fails does laminitis ensue [ cite journal | last =Kronfeld | first =DS | coauthors =et al | year =2006 | month = | title =Metabolic Syndrome in Healthy Ponies Facilitates Nutritional Countermeasures against Pasture Laminitis | journal =The American Society for Nutrition | volume =136 | issue = | pages =p. 2090S-2093S| id = | url =http://jn.nutrition.org/cgi/reprint/136/7/2090S | accessdate = 2008-05-31 | quote = ] - this may support the argument that EMS is an evolved survival trait. cite journal | last =Johnson | first =PJ | year =2007 | title =Endocrinopathic Laminitis - What is it and what should be done about it? | journal =Michigan Veterinary Medical Association Proceedings | url =http://www.michvma.org/documents/MVC%20Proceedings/Johnson1.pdf | accessdate = 2008-05-31]ymptoms
EMS horses tend to become obese very easily and, even when starved down, may have abnormal fat deposits in the neck, shoulders, loin, above the eyes and around the tail head, even when the rest of the body appears to be in normal condition. Some cases may become pot-bellied, perhaps polydipsic, acyclic and generally lethargic.cite web |url=http://www.liphookequinehosp.co.uk/LabMetabolicsynd.htm |title=Metabolic Syndrome in Horses |accessdate=2008-05-31 |publisher=Liphook Equine Hospital |date=2005 ]
Often, the initial presentation is as a laminitic displaying signs of Cushings, but with a normal pituitary-adrenal axis.
Treatment
The basis of treatment is managing the horse's adipocyte level - i.e., weightand obesity control by dietary restriction and exercise.cite web |last=Johnson |first=PJ |url=http://www.safergrass.org/pdf/METSYNDeq.pdf |title=Metabolic Syndrome in Horses |accessdate=2008-05-31 ] Substantial clinical improvement can be achieved with as little as 5-10% weight reduction. In addition,
antioxidant treatment (e.g.Vitamin E orChromium supplementation) have been suggested.Pharmacological treatments tend to be symptomatic. The condition cannot be cured, but can be managed. Some veterinarians have reported success withpergolide andcyproheptadine , although the mechanism of any such action is unclear. Exogenousthyroid hormone administration has also been used, on the rationale that thyroid hormones facilitate insulin-mediatedglucose absorption by cells - however, they also facilitate glucose uptake by the gut, and in depth cost/benefit studies have not as yet been published.References
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