One of the hormones secreted by the pancreas is insulin. Diabetes mellitus results from a relative or absolute deficiency of the secretion of insulin from the pancreas. This deficiency causes decreased tissue use of substances including glucose, amino acids, and fatty acids. As glucose accumulates in the blood, it reaches concentrations that are so high that it cannot be eliminated from the urine. Then glucose loss in the urine, a condition called glucosuria, develops. Once this occurs, the amount of urine produced increases, and the cat begins to drink more to avoid dehydration. Since the tissues of diabetic cats are not able to use glucose properly, weight loss will ensue. Because the cells in the portion of the brain that mediate hunger are also sensitive to insulin, the cat may develop an excessive appetite; without insulin, glucose cannot enter these cells, and perceived hunger persists. These facts account for the classic clinical signs of diabetes: increased urination, increased thirst, weight loss, and increased appetite.
Type I diabetes mellitus is a condition in which destruction or loss of insulin-secreting cells in the pancreas results in a complete lack of insulin. This can occur either very quickly, or gradually over time. This condition, called insulin-dependent diabetes mellitus or IDDM, usually requires treatment with insulin and accounts for approximately 60 percent of cats with diabetes mellitus. IDDM may occur because of protein deposition in the pancreas with degeneration of insulin-producing cells, or as the result of chronic pancreatitis. Other changes may be involved in the development of IDDM, including immune system-mediated inflammation in the pancreas.
With Type II diabetes mellitus -- also know as non-insulin-dependent diabetes mellitus or NIDDM -- there is resistance to the action of insulin on body tissues, as well as abnormalities in insulin secretion from the pancreas. Type II diabetics may not require insulin. Type II diabetes is more common in cats than in dogs. Obesity, hereditary factors, and abnormal protein deposition may be important factors in its occurrence. For cats, there are currently no reliable tests to distinguish whether Type I or Type II diabetes is present. Some cats appear to change from one type to the other over time, and the revert back again.
Secondary diabetes also can occur in cats, usually as a result of diseases or medications that influence insulin activity. Medications, including some long-acting steroids and some progesterone derivatives, are the most common drugs implicated in the development of secondary diabetes in cats. Another confusing fact about diabetes mellitus in cats is that the need for insulin in an individual cat may come and go over time. Some of these transiently diabetic cats eventually require life-long treatment, but others seem to overcome this state and ultimately require no further treatment.
