Slowed coat change, altered figure, fewer muscles and reduced condition – what is often dismissed as a mere symptom of old age is in many cases a hormonal disease: Equine Cushing's Syndrome. This is a metabolic disorder that cannot be cured, but fortunately is easily treatable. A drug from the group of dopamine agonists is available for this purpose: Pergolide.
Pergolide is currently the only approved agent for the treatment of Equine Cushing's Syndrome. In this disease, affected horses release too much of the "stress precursor hormone" ACTH (adrenocorticotropic hormone) from their pituitary gland. ACTH in turn leads to an increased release of the stress hormone cortisol from the adrenal gland. Cortisol takes over a number of important functions in the body that make it ready to fight or fight back. to make the horse ready to flee: Glucose (blood sugar) is provided as a quick source of energy, blood prere rises, the heart beats faster, fat metabolism is activated and inflammatory reactions in the body are inhibited. The body is briefly more powerful and ready to fight or. Escape. Naturally, cortisol is released in stress-. released during stressful situations. Naturally, cortisol is released in stress-. stress situation is released. Horses suffering from Equine Cushing's Syndrome also have a deficiency of the neurotransmitter dopamine, which normally reduces ACTH production. Also, an elevated blood cortisol level itself leads to a throttling of ACTH release (which in turn inhibits cortisol release). This control loop (a so-called negative feedback loop) is disturbed in horses suffering from Cushing's syndrome. As a result, affected horses are under persistently elevated cortisol and blood glucose levels, which is associated with a number of clinical symptoms.
The clinical picture of Equine Cushing's Syndrome
Initially, Equine Cushing's Syndrome develops insidiously and it may even take years for the horse to show symptoms. Most noticeable is certainly the altered coat growth with the long, curly coat characteristic of Cushing's horses (hirsutism). The initial symptoms, such as fatigue, increased sweating even without physical exertion, increased drinking and correspondingly increased urination, as well as susceptibility to infections, wound healing disorders and skin problems, are often "overlooked" or "ignored". not immediately assigned to Cushing's syndrome. Only in the further course of the disease are other typical symptoms added: poor horn quality, tendency to hoof ulcers and laminitis as well as the altered physique with emaciation, low back, pot belly, fatty neck and fat pads above the eyes. In addition, horses are often impaired in fertility and show elevated liver and kidney values. Most commonly affects older horses and ponies 15 years of age and older, but may occasionally occur at younger ages. This disease can be clearly detected with an ACTH test. For this purpose, the veterinarian takes one or more blood samples, which are then examined for certain hormone and blood values.
What exactly does pergolide do in the body?
Pergolide is an active ingredient from the group of dopamine agonists. In pharmacology, agonists are substances that bind to a specific receptor and thus trigger the normal biological reactions. Pergolide thus binds to the dopamine receptors and takes over the functions of dopamine. Dopamine is an important messenger substance in the brain, a neurotransmitter, which u. a. is responsible for inhibiting ACTH production in the pituitary gland. The impaired inhibition of ACTH production in Cushing's patients due to dopamine deficiency is compensated by pergolide. Pergolide throttles ACTH production in the brain instead of dopamine. As a result, cortisol release from the adrenal gland is in turn inhibited. The level of cortisol in the blood normalizes. The accompanying symptoms caused by the cortisol levels, which have often been elevated for years, naturally need a certain amount of time to subside. An initial improvement in symptoms can usually be expected 6 to 12 weeks after the start of therapy. If the therapy is discontinued, the replacement dopamine is of course missing and there is again an increased ACTH production. Therefore, the therapy must be lifelong. There are two preparations with this active ingredient in Germany (Prascend®, Boehringer Ingelheim and Pergoquin®, WDT). At the beginning of therapy, the horse must first be adjusted to the correct dose. For this purpose, the ACTH concentration in the blood is determined at certain times (initially usually every 4 to 6 weeks) and, if necessary, the cortisol level is increased. the dose adjusted. After the patient has been adjusted to the correct dose of pergolide, a therapy check including a blood test should be carried out by the veterinarian every six months. The active ingredient is generally well tolerated. At the beginning of treatment, in rare cases, there may be a decreased appetite. Other possible, but rarely occurring, side effects are slight dejection or slight gait disturbances, diarrhea and colic as well as increased sweating. If side effects occur, the veterinarian will adjust and reduce the dose.
How the active substance is administered?
The active ingredient pergolide, which is available in tablet form, is approved for the horse. The tablets can be entered with some food, such as an apple. They can also be dissolved in water and z. B. feed mixed with molasses. It is also possible to give the tablets dissolved in water directly to the horse's mouth – like a worming cure – with the help of a syringe. The active ingredient pergolide replaces an important endogenous messenger substance. Can thus significantly reduce the symptoms of Equine Cushing's Syndrome. Unfortunately, this disease is not curable, so that a therapy with pergolide must be carried out throughout the horse's life.