Cushings questions... Pergolide and Prascend are not allowed and must be withdrawn during competitions under FEI rules, is this likely to make life difficult for the increasingly high numbers of young horses being diagnosed with Cushings after owners take advantage of the free blood testing? Does this hinder the sale of young talented horses with the potential to become world class and are they now to be classed as unsound? If there are no other symptoms of Cushings other than a raised ACTH should the owner disclose the disease or keep quiet? Could there be other reasons for a raised ACTH and is it possible to manage the disease by diet or natural methods? Equine Cushings syndrome is a fairly common but complex condition which can be difficult to treat with conventional medicine. Cushings syndrome eventually causes the enlargement of the pituitary gland through abnormal cell growth (in a similar way to cancer) or a benign tumour of the pituitary gland. The pituitary gland then releases large amounts of hormones in an unregulated manner and creates an abnormal response from the immune system against the tumour, which adds to the complexity of the syndrome and causes many symptoms including laminitis. The abnormal release of hormones causes chaos and unregulated feedback loops, signals happen in an out of order or uncontrolled manner, dopamine drops in the summer and autumn, effecting normal seasonal changes such as coat loss. In horses without Cushings the signalling hormones from the pituitary rise and fall throughout the days and change within the different season, with Cushings the signalling hormones become unpredictable and some are continuously released rather than having a lower and higher level. This is the reason why affected horses don’t lose their coats in the summer and are more laminitis prone and can be either over or under weight. Horse that are under weight have an over production of proopiomelanocortin peptides and some horses that have Cushings and are overweight will have inherited a gene mutation which has predisposed them from birth to EMS/Cushings/laminitis. Serotonin levels tend to be lower all year round leaving the horse vulnerable to low energy and depression and sensitivity to changes in routine. A horse with Cushings may urinate and drink more frequently this is caused in part from insulin resistance and an inability of the body to store glucose, the glucose enters the kidneys and causes a change in osmotic pressure and a rise in water retention which is finally released as urine. The traditional veterinary treatment is Prascend or Pergolide mesylate which is a synthetic ergot derivative and is a potent dopamine receptor agonist which inhibits the release of prolactin. In horses with Cushings or PPID pergolide is believed to stimulate dopamine receptors, and has been shown to decrease levels of adrenocorticotropic hormone (ACTH), melanocyte stimulating hormone (MSH), and other pro-opiomelanocortin peptides. There are compounds which come from plants which have a similar effect (pergolide was developed from French lilac) and are known dopamine receptor agonists and can bind to D2 receptors using the corpus striatum membrane DA receptor binding assay. Clinical tests (WHO) supported the use of plants such as Agnus Castus to inhibit prolactin and one of the most important features of using natural compounds rather than a synthetic medicine was that the plant extract affects only the D2 receptor which are located in the pituitary gland whilst pergolide influences D1 and 2 receptors. D1 receptors influence temperature, thirst and hunger, and the thalamus which influences sleep and alertness, pergolide also influences 5-HT 2B which can cause heart valve defects and gastrointestinal upsets. Some owners prefer synthetic and some prefer the natural I guess it’s good to have a choice and whatever method of control is used it is always worth bearing in mind that Cushing’s is a syndrome with multiple symptoms and each horse must be managed with this in mind. Horses with Cushings may also have low red blood cells, low lymphocytes and elevated blood glucose levels Other reasons why ACTH might be high Veterinarians are diagnosing Cushings in young horses not showing the full blown range of symptoms described above but from blood tests showing raised ACTH levels is this the beginning of the decline into a lifelong degenerative disease or might there be other reasons for the ACTH levels to rise, that are not related to Cushings disease? As we know there is a link between Cushing’s disease, insulin resistance, laminitis and equine metabolic disease and the common denominator is obesity, Cushing’s horses are often ‘good doers’ most of their lives but suddenly lose weight and go thin with the onset of the disease. A horse with a body condition score of between 7 and 9 are considered to be obese and have fat pads and ‘cresty’ necks which are made up of adipose tissue. Adipose tissue is in fact part of the immune system and contains numerous signalling chemicals called cytokines some of which cause inflammation and laminitis. One particular chemical released by the adipose tissue is called Interleukin -6 and it is able to raise ACTH levels because it has a direct link with the hypothalamic-pituitary-adrenal axis (this axis controls and regulates many body processes including digestion, energy storage and expenditure). The second reason for a high ACTH level not linked to Cushings is diet, a horse fed a cereal based or high carbohydrate diet will have naturally higher ACTH levels. During ingestion and digestion of cereals and carbohydrates the horse has a ‘pay it’ forward signalling mechanism in the gut (GIP) which signals the release of insulin and drives up ACTH in the blood stream ahead of the expected delivery of glucose. Some rapid digestible cereals cause a higher release of postprandial insulin than others. If you have a young horse with no other symptoms of Cushing’s it is well worth a complete review of the diet, try to lower carbohydrate levels, instead introduce as many fresh plants/shrubs/herbage as possible as these include many valuable anti oxidants which are able to protect against oxidative damage, shrink adipocytes thus helping to support normal ACTH levels, help regulate weight and normalise insulin release. Please note there is no intention to offend the owners of the horses illustrated, they are just photos, neither horse has Cushings that I am aware of but if the horse in the photo is yours and you are offended then please let me know and I’ll replace it. Simples!
Posted on: Thu, 16 Oct 2014 13:28:53 +0000
Trending Topics
Recently Viewed Topics
© 2015