Pathogenensis

Dogs typically develop insulin dependent, or type I, diabetes mellitus. Their pancreas is not able to produce insulin so they have an absolute requirement for insulin to maintain euglycemia. Histologically they have fewer, smaller pancreatic islets. Hyperadrenocorticism, diestrus and pregnancy might cause transient diabetes in dogs but almost all dogs require insulin and will require insulin life long.

Cats more commonly develop non-insulin dependent, or type II, diabetes but they can become type I. Cats often deposit amyloid in their pancreas that leads to progressive destruction of acinar cells. Chronic pancreatitis can lead to diabetes in the cat as well. Their pancreas can often produce insulin but either they don't produce enough to maintain euglycemia or they are resistant to insulin's effects. Transient diabetes is more common in this species because of waxing and waning insulin requirements. Obesity contributes to insulin resistance in both species.

Currently, dietary recommendations for cats are for high protein and low carbohydrates. Cats can not convert dietary glucose for storage and energy as well as dogs. Cats primarily use amino acids and fat in the diet for energy so carbohydrates are left over to contribute to hyperglycemia. Currently Hills md® and Purina DM® are diets that fit into this category of low carbohydrate, high protein. These diets help reduce postprandial glucose and insulin concentrations, decrease insulin requirements, result in better control of diabetes and can produce remission in some cats. Cats are fed the majority of their caloric intake twice daily prior to insulin administration but because they often eat throughout the day, the remainder of their daily calories is left for free feeding. This regimen might be necessary in some dogs that are grazers. Correction of obesity should also be a goal of dietary therapy and can decrease insulin resistance.

The dog is an omnivore by nature and is more capable of utilizing carbohydrates for energy and storage than the cat. For this reason, dietary recommendations for dogs focus on minimizing dramatic post-prandial increases in glucose as well as weight control. Diets higher in fiber, particularly soluble fiber, are used and there are many that fit into this category. Dogs are usually fed twice daily prior to insulin administration. Again, correction of obesity is also a goal in the dog.

It is important to remember that there is not an ideal diet or feeding schedule for all patients. Dogs and cats that are underweight will not tolerate a diet that promotes weight loss so other diets may be necessary.

Oral Hypoglycemics

The majority of the oral hypoglycemics previously used to treat diabetes have fallen out of favor. The sulfonylureas (glipizide, glyburide) were used in cats because their primary mechanism of action is stimulation of insulin production by the pancreas which means they must have some capacity to make insulin on their own. Unfortunately it is now believed that increased stimulation of the pancreatic islets also leads to burn out of the beta cells which can actually result in a decrease of insulin production and progression of diabetes so these drugs are not used.

Biguanides, like metformin, do not stimulate insulin production by the pancreas. Instead they enhance sensitivity of the liver and peripheral tissues to insulin. There has been a high incidence of intestinal side effects with this medication and the results in cats are inconsistent but metformin does appear to work better with some residual insulin production. Again, because it requires insulin production, it is not particularly useful in the dog.

Acarbose is an alpha-glucosidase inhibitor that affects brush border enzymes in the small intestine decreasing glucose absorption. There has been some success with its use in diabetic cats and dogs.

Chromium and vanadium are trace elements thought to increase tissue sensitivity to insulin. Chromium may have some effect in cats with diabetes and vanadium may be beneficial in diabetic cats and dogs.