The pancreas is composed of several types of cells that have distinct functions involved in the production of hormones and digestive enzymes. The exocrine pancreas produces enzymes that are essential for the digestion of complex dietary components such as proteins, triglycerides, and complex carbohydrates. The exocrine pancreas also secretes large amounts of bicarbonate, which buffers stomach acid. Disorders of the exocrine pancreas are discussed in the section on digestive disorders Digestive Disorders of Dogs , because they relate to digestion. The endocrine pancreas produces the hormones insulin and glucagon, which regulate blood sugar levels. The functions and disorders of the endocrine pancreas are discussed in this section.
The islets of Langerhans in the pancreas consist of 3 types of cells, each of which produces a different hormone. Most of the cells, which are called beta cells, produce insulin. Insulin affects, either directly or indirectly, the function of every organ in the body, particularly the liver, fat cells, and muscle. In general, insulin increases the transfer of glucose (sugar) and other compounds into body cells. It also decreases the rate of fat, protein, and carbohydrate breakdown.
The other 2 cell types in the islets of Langerhans produce the hormones glucagon and somatostatin. When blood glucose levels drop, glucagon is released. Glucagon helps convert stored carbohydrates into glucose so they can be used as energy.
Insulin and glucagon work together to keep the concentration of glucose in the blood and other body fluids within a relatively narrow range. Glucagon controls glucose release from the liver, and insulin controls glucose transport into numerous body tissues.
Diabetes mellitus (often called simply diabetes) is a chronic disorder of carbohydrate metabolism caused by either a deficiency of insulin or a resistance to insulin. Middle-aged dogs are affected most commonly, with females affected twice as often as males. Certain small breeds, such as Miniature Poodles, Dachshunds, Schnauzers, Cairn Terriers, and Beagles, seem to develop diabetes more often than other breeds, but any breed can be affected.
A number of mechanisms are responsible for decreased insulin production and secretion, but usually they involve destruction of islet cells either by the immune system or severe, recurrent inflammation of the pancreas (pancreatitis). Insulin resistance and diabetes mellitus are also seen in many dogs with Cushing disease ( see Cushing Disease Cushing Disease The pituitary gland is located near the center and bottom of the brain. It produces a number of critical hormones that control many parts of the body, including several other endocrine glands... read more ). Longterm treatment with glucocorticoids or progestins can make an animal more likely to develop diabetes mellitus. During pregnancy and during heat cycles, unspayed female dogs produce the hormone progesterone, which can lead to high blood sugar and insulin resistance. Obesity increases the risk of insulin resistance. Increased glucagon also appears to contribute to development of high blood sugar by releasing liver stores of glucose. Stress, obesity, and the use of certain drugs (glucocorticoids and progestogens) can increase signs of diabetes.
Diabetes can often develop gradually, and the signs may not be noticed at first. Common signs include increased thirst and urination, along with increased appetite and weight loss. Diabetic animals often develop longterm or recurrent infections. An enlarged liver is common. Cataracts develop often in dogs with poorly controlled diabetes mellitus. A diagnosis of diabetes mellitus is based on finding high levels of sugar in the blood and urine after a period of fasting.
Your understanding of the disease and daily care of your pet are critical to successfully managing diabetes. Treatment involves a combination of weight loss, diet, insulin injections, and possibly oral medications. Your veterinarian will determine the amount and timing of your pet’s meals, and the dosage and timing of insulin injections. Follow these recommendations very closely. In addition, your dog should be spayed if she is not already. Blood glucose measurements are necessary to ensure that the disease is being controlled. Your veterinarian may recommend that you perform this monitoring at home to get the most reliable results. Your veterinarian will interpret these results to make any necessary changes in treatment over time.
Do not make changes in the amount or timing of insulin treatments or diet without consulting your veterinarian. Overdosing insulin can result in life-threatening low blood sugar (hypoglycemia); underdosing insulin can have serious longterm effects on the regulation of your dog's diabetes. Signs of dangerously low blood sugar include weakness, lack of coordination, seizures, and collapse. If these signs are seen after administering insulin, call your veterinarian immediately. He or she may make recommendations to quickly increase your dog's blood sugar level before arriving at the veterinary office. Significantly low blood sugar is a medical emergency and requires immediate treatment.
Untreated or poorly treated diabetes mellitus can result in a serious life-threatening complication called diabetic ketoacidosis. This is a medical emergency that requires immediate treatment and hospitalization to correct. Signs of ketoacidosis include increased thirst and urination, lethargy, weakness, decreased appetite, and trouble breathing. If your dog is exhibiting any of these signs, it should be seen by a veterinarian right away.
Functional Islet Cell Tumors (Insulinomas)
Tumors in the islet cells of the pancreas often produce and secrete the hormones normally secreted by the gland. The most common pancreatic islet tumor affects the insulin-secreting beta cells and is called an insulinoma. Insulinomas are most common in dogs 5–12 years of age. Other hormones and products can also be produced and secreted by islet cell tumors.
Signs result from excessive insulin secretion, which leads to low blood sugar (hypoglycemia). Initially, signs include weakness, fatigue after exercise, muscle twitching, lack of coordination, confusion, and possibly changes of temperament. Dogs are easily agitated, occasionally becoming excited and restless. Periodic seizures may occur. A dog might also collapse, appearing to have fainted.
Signs occur infrequently at first, but become more frequent and last longer as the disease progresses. Attacks may be brought on by exercise, or by fasting or eating (which stimulates the release of insulin and lowers blood sugar levels). Signs resolve quickly after glucose treatment. Repeated episodes of prolonged and severe low blood sugar can result in irreversible brain damage. Diagnosis is based on a history of periodic weakness, collapse, or seizures, along with tests indicating low blood sugar.
Removing the tumor surgically can correct the low blood sugar and nervous system signs unless permanent damage has already occurred. However, if the tumor has already spread, blood sugar levels may remain low after surgery. Unfortunately, insulinomas are often malignant, but dogs can live for more than a year with good quality of life if all of the large tumors are removed. Quality of life can sometimes be maintained in affected dogs by modifying the diet and giving glucocorticoids or other drugs.
Gastrin-secreting Islet Cell Tumors (Gastrinomas)
Gastrin is a hormone that prompts the release of gastric acid in the stomach. Gastrin is normally secreted only by the stomach and small intestine. In rare cases, it can also be secreted by tumors of the pancreatic islet cells called gastrinomas.
Signs of a gastrinoma may include loss of appetite, vomiting blood, intermittent diarrhea (usually containing dark blood), weight loss, and dehydration. Many of these signs result from stomach ulcers caused by too much gastrin. In dogs with repeated stomach or intestinal ulcers, exploratory surgery can be done to check for pancreatic tumors. However, in all known cases, the pancreatic cancer has been inoperable because of spread to other areas. Medications for the stomach and intestinal ulcers can make the dog more comfortable.