Endocrine Diseases

The endocrine glands located in various places throughout the dog's body, are the manufacturers of hormones, which, when released, travel in the bloodstream to reach another gland or part of the body. These hormones, sometimes called the chemical messengers of the body, regulate body functions in numerous ways.

Thyroid gland
Located under a dog's chin, this gland makes two main hormones, T4 and T3. The most common problem associated with the thyroid gland is underproduction, resulting in hypothyroidism. Hyperthyroidism, or or an overproduction of these hormones, is very rare in the dog. When it occurs, it is often the result of thyroid cancer and, although it can sometimes be successfully treated with radiation and/or chemotherapy, often the dog is already too ill for treatment to be appropriate.

Parathyroid gland
There are 4 parathyroid glands, which lie in the soft tissue around the thyroid gland in a dog's neck and secrete parathyroid hormone, which is important in the regulation of blood calcium. A deficiency of this hormone, or hypoparathyroidism, causes the blood calcium to drop and a dog to develop a condition called tetany in which the muscles twitch and spasm the way they do in an epileptic seizure. This condition is quite rare. A tumor on a parathyroid gland will cause hyperparathyroidism in which the blood calcium will go up and settle in the kidneys, causing the animal to develop kidney failure.

Adrenal glands
Two adrenal glands are located at the front of each kidney. They are divided into two parts, similar to a plum or peach—the inner part corresponding to the pit, the outer to the flesh of the fruit. Each part makes different hormones. The outer part, or adrenal cortex, manufactures cortisol/cortisone and aldosterone. Too much cortisone, or hyperadrenocortisism, results in Cushing's disease. A deficiency of cortisone and aldosterone, or hyperadrenocortisism, is called Addison's disease. Both of these diseases are quite common in the dog.

The inner part of the adrenal gland is called the adrenal medulla; it produces adrenaline, or epinephrine. A deficiency of adrenaline won't cause any signs. Too much adrenaline can be produced by a very rare tumor called pheochromocytoma, which will cause a dog to develop a rapid heartbeat, become nervous and sweaty, and run a mild fever.

Pancreas
This gland serves two distinct functions. One part of the pancreas is an endocrine gland; the other is an exocrine gland that releases digestive enzymes into the small intestine to help in the absorption of food. The endocrine part of the pancreas makes many hormones, the most important of which is insulin. Not enough insulin will result in diabetes mellitus. An overproduction of insulin can be caused by a tumor of the pancreas, a condition that usually occurs in older large breed dogs. Signs of this disorder are similar to those found in hypoglycemia. In dogs, these tumors, called insulinomas, are almost always malignant, but in many cases they can be removed with a resulting remission for up to 1 or 2 years before a recurrence of the tumor occurs. This cancer can often spread to the liver, making it impossible to remove the tumor, but even then it can be treated with drugs. In both instances, the dog can be kept alive and feeling pretty good for some time.

Gonads
These include both testicles in males and ovaries in females. In the male, the testicles make testosterone, which is necessary for fertility. A testicular cancer usually makes female hormones, causing a male dog to act more like a female.

Pituitary gland
Located at the base of the brain, the pituitary is known as the "master gland" because it controls and regulates the function of many of the other glands through the action of its six major types of hormones. Adrenocorticotrophic hormone (ACTH) is released from the pituitary and regulates the adrenal cortex, which manufactures cortisone. A deficiency of this hormone is very unusual, but if there were one, the signs would be similar to those of Addison's disease. An excess will cause the most common type of Cushing's syndrome. Thyroid stimulating hormone, or TSH, stimulates the thyroid gland to make T4 and T3. An excess or deficiency of TSH has not been very well defined, but occasionally a tumor on the pituitary can destroy the TSH-producing cells, resulting in an underactive thyroid gland. A deficiency of the growth hormone, or GH, in a young dog will result in a dwarf, which happens very rarely. A tumor of the GH-producing cells has never been recorded; however, a condition is seen in older, unspayed female dogs where too much progesterone and estrogen can stimulate GH cell hyperplasia, or the production of too many GH cells, forcing GH levels to go up and causing acromegaly, a condition in which the bones and tissues in an adult animal want to grow but do not have room. The result is thickening of bones and skin, which causes wide spaces between teeth and enlarged internal organs.

Other hormones secreted by the pituitary gland are follicular stimulating hormone, or FSH, and luteinizing hormone, or LH, both of which are important to stimulating ovaries and testicles. Excesses or lacks of these hormones are rare and don't seem to cause any clinical problems. The pituitary gland also secretes prolactin, which is very important to milk secretion in the lactating female.

Basically, most overproduction of a hormone known as hyper-, is caused by a tumor or tumors of one of the endocrine glands. Underproduction of a hormone resulting in a deficiency, or hypo-, is usually of unknown cause, or idiopathic. There is some evidence that hormone deficiencies are caused by an autoimmune disease, in which the body attacks its own endocrine system for unknown reasons.

In general, endocrine diseases of the dog are treatable either by removal of the tumor or by medication. Left untreated, most endocrine diseases will cause death in a dog within a period of 1 to 2 years.

Diagnosis of endocrine diseases is most often made by means of a combination of clinical signs and blood tests.

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