Cortisol Deficiency in Dogs
A dog's body is designed to maintain normal metabolism using complex systems that control every cell, nerve and chemical in the body. When one of these systems does not function correctly, the normal processes in the body are disrupted. A minute change in one system can create a multitude of problems throughout the dog's body.
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Cortisol
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The pituitary gland sends out adrenocorticotropic hormone (ACTH), which signals the adrenal glands to produce cortisol and aldestorone. Cortisol is a type of hormone, called a glucococosteriod; aldesterone is a mineralcorteriod. Cortisol is known as the "stress" hormone because the body produces more during stressful situations such as trauma, surgery, fear or excitement. During these stress-producing situations, cortisol reacts by increasing the flow of glucose, protein and fat from body tissues into the bloodstream. This action supplies the body with additional energy to counteract the effects of the stressor. Aldestorone regulates the amount of sodium and potassium levels in the blood.
Addison's Disease
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Addison's disease, or hypoadrenocorticism, is caused by the underproduction of corticosteroid hormones. There are three types of Addison's disease: primary, secondary and atypical. Primary and atypical are caused by immune mediated destruction of the adrenal glands. Secondary is caused by the failure of the pituitary gland to release ACTH. This leads to the adrenal glands not producing enough cortisol and aldestorone.
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Symptoms
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The symptoms of Addison's disease mimic those of many other diseases. Signs will initially include lethargy, muscle weakness, vomiting, diarrhea, pain in the rear legs and tremors. Many times the diagnosis of Addison's disease is missed until the dog suffers from an "addisonian crisis." This crisis occurs when the levels of potassium in the body interfere with normal heart function. The heart starts beating erratically, and the blood pressure drops. Intravenous fluids must be started immediately to restore normal electrolyte levels or the dog may die.
Diagnosis
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Diagnosing Addison's disease is often a complex process. Your veterinarian will draw a blood sample to test the levels of sodium and potassium in the blood. These electrolyte levels are important yet not definitive. Secondary and atypical Addison's may show no alterations in electrolyte levels. For a definitive diagnosis, an ACTH stimulation test will be performed. Blood is drawn and the level of cortisol is measured. Then, a synthetic form of ACHT is injected into the dog. This should cause the adrenal glands to produce cortisol. After an hour, the blood is tested again for cortisol levels. If the levels are still low or unchanged, a diagnosis of Addison's disease is made.
Treatment
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Treatment will depend of the type of Addison's disease present, but will include replacement of cortisol and or aldestorone. Replacement of aldestorone is achieved by administering an oral medication called Florinef or an injectible medication called Percorten-V. Replacement of cortisol is achieved by administering an oral medication called prednisone or hydrocortisone. Although medications will need to be given for the rest of your dog's life, the quality and duration of his life will not be greatly affected.
Warning
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Your dog may suffer an "addisonian crisis" if you abruptly discontinue the use of steroids. You should gradually reduce the amount of the medication to prevent this from occurring.
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