The pituitary gland located at the base of the brain releases ACTH (hormones that stimulate the adrenal cortex) into the blood stream. Another part of the brain, the hypothalamus, is responsible for directing the pituitary gland to do this. Once released into the blood stream, ACTH stimulates the two adrenal glands situated near the kidney of the dog to secrete cortisol, a glucocorticoid, into the blood stream.
A dog’s body automatically increases production of cortisol in conditions of stress, infection, pain, surgery or trauma. This is the natural and automatic response of the body to sustain life and maintain important body functions.
The body system of a healthy dog is agile and can sustain metabolic equilibrium. It can actively maintain several complex biological mechanisms that operate via the autonomic nervous system to offset disrupting changes. This complex system of reciprocal responses can be disturbed due to adrenal or pituitary tumors or due to veterinary interference. Administering an excess of cortisol indirectly means ‘poisoning’ the dog’s body that can ultimately result in Cushing’s disease or hyperadrenocorticism in a dog . Cushing’s disease in dogs may occur due to issues in the adrenal gland or the pituitary gland.
A low cortisol level leads to another disease called hypoadrenocorticism in dogs or Addison’s disease. The most common causes of low cortisol or primary hypoadrenocorticism in a dog are atrophy of the adrenal cortex or veterinary interference by external administration of steroids. Secondary hypoadrenocorticism is the result of an inability of the pituitary to produce enough ACTH to stimulate the adrenal glands. The reasons behind this pituitary failure are likely to be trauma, tumors, lesions or veterinary intervention.
Low levels of cortisol disturb the electrolyte balances, and the ratio of sodium to potassium in the body can go beyond acceptable levels. An electrolyte imbalance is the primary indicator of the condition, but definite diagnosis is arrived through ACTH stimulation tests that involve a number of blood tests.
The first signs of low levels of cortisol or Addison’s disease are a loss in appetite, vomiting, diarrhea, lethargy, weakness and a significant loss in weight. The veterinarian may discover clinical signs of depression, abnormally slow heart beat and dehydration.
Treatment of Addison’s disease depends upon whether the dog suffers from a primary or a secondary condition of hypoadrenocorticism. In the primary condition, the electrolyte balances are overly disturbed, and it is treated with hormonal replacement therapy. This involves replacement of aldosterone, the hormone responsible for maintaining the balance. In addition, oral prednisone is administered to augment the reduced cortisol levels produced by the dog’s body.
In the secondary condition of Addison’s disease however, only glucocorticoids are prescribed.
Dogs that are diagnosed with low levels of cortisol or Addison’s disease have to live with the condition throughout their lives. The maximum that dog owners can do is to intervene with prompt and timely medication. Monitoring and managing the effects of various drugs is essential to ensure a comfortable life for the dog.