The adrenal glands are made up of two parts, the cortex and the medulla, and are located just in front of the kidneys.
The adrenal cortex has three different layers, each of which produces a unique set of steroid hormones. Mineralocorticoids is produced by the outer layer. This hormone helps the body regulate levels of sodium and potassium salts. In the middle glucocorticoids are produced. These hormones are essential to the metabolizing of nutrients, and they also help to reduce inflammation in the body. The final, inner layer of the adrenal gland is where estrogen and progesterone, the sex hormones, are produced.
The adrenal medulla is critical to lowering blood sugar, or glucose, levels and is also instrumental in responding to stress. This part of the adrenal gland releases epinephrine, which is sometimes referred to as adrenaline, and norepinephrine. Both of these hormones work together to increase several metabolic and bodily functions, such as heart output, blood glucose, blood pressure, and the slowing of digestion.
Also called hyperadrenocorticism, Cushing’s is a fairly common endocrine system disease that most frequently shows up in adult and aging dogs. Chronic excess of cortisol, another hormone, is the main cause for dogs to show signs of the disease. When cortisol levels increase in dogs it can be caused by any one of several endocrine mechanisms. Most commonly the cause is a pituitary gland tumor. In fact, this is the cause of Cushing’s disease 85 to 90 percent of the time. When the tumor increases it produces a hormone that sends a message to the adrenal gland causing it to develop excessively. In only 10 to 15 percent of cases is a tumor in the actual adrenal glands the cause of this disease. Dogs who have had to take corticosteroids for extended periods of time, such as those used to treat inflammation or an immune disorder, can also lead to a dog exhibiting signs of Cushing’s.
Addison’s disease is also frequently referred to as hypoadrenocorticism. This disease can be caused by insufficient adrenal gland hormones and usually presents in young or middle-aged canines. More often than not the cause is unknown. However, it is likely that many cases of Addison’s result from an auto-immune disease that leads to the destruction of some of the body’s own tissue. Other conditions can also lead to the destruction of the adrenal gland, as well, such as cancer in another part of the body.
Aldosterone is the main mineralocorticoid hormone, levels of which are reduced with Addison’s disease, affecting potassium, sodium, and chloride levels in the blood. Over time potassium levels in the blood increase and build up, and in extreme cases this can cause the heart to develop an irregular beat or to slow to a dangerously low rate. In fact, some dogs develop heart rates so low that they go into shock or become extremely weak. This usually occurs with rates 50 beats per minute or below.
Loss of appetite, repeated bouts of diarrhea and vomiting, loss of body condition over time, and dehydration are the most common symptoms of Addison’s disease. Often times severe weight loss will occur. Sometimes the signs of Addison’s can be difficult to identify during the development stages of the disease, but sudden and severe symptoms can appear later on, such as kidney failure and shock.
Tentative diagnoses can be made by veterinarians by looking at the dog’s health history, testing for laboratory irregularities or abnormalities (such as low levels of sodium or high levels of potassium), and certain tell-tale signs and symptoms. Evaluation of adrenal function using specific testing will be used to confirm the diagnosis. The veterinarian will do this by measuring cortisol levels in the blood and administering adrenocorticotropin, a hormone that is used to stimulate the adrenal gland function in animals, and then re-measuring the cortisol levels. Dogs suffering from Addison’s will show low cortisol levels the first time around, and exhibit little to no response after being given the injection.
Sometimes Addison’s can cause an adrenal crisis, which is an emergency medical situation requiring prompt treatment with fluids via intravenous methods to restore the body’s fluids, salt, and sugar levels. When the pet is stabilized, hormone treatment can often begin. Veterinary professionals will keep a close eye on the pet’s laboratory measures and adjust the dosage if needed. Going forward, long-term care will likely be a prescribed hormone replacement therapy program administered either orally or via injection. Sodium may also need to be added to the diet in order to maintain proper levels in the blood.
Pheochromocytomas In Dogs
Pheochromocytomas are adrenal medulla tumors that can secrete either epinephrine (which is adrenaline), norepinephrine, and sometimes both. These tumors can often be symptomless and are often found almost by accident during treatment for other health issues. If symptoms do present they usually include excessive thirst and/or urination, restlessness, a distended abdomen, and a high or increased heart rate. The veterinarian will usually use an ultrasound to diagnose the tumor, and if treatment is feasible it usually involves surgery and blood pressure management. Neuroblastomas and ganglioneuromas are other adrenal gland tumors that can develop from nerve cells.