What Is Diabetes Insipidus in Dogs?
Canine diabetes insipidus is a metabolic disorder in dogs caused either by insufficient production of anti-diuretic hormone (ADH) in the brain, or the kidneys inability to respond to ADH. Prognosis is questionable for the former and quite good for the latter. Its cause isn't always clear and the condition can therefore be difficult to diagnose.
Anti-Diuretic Hormone and Urination
The body, including the dog body, determines when to conserve water and when to excrete water based on the concentration of solutes such as sodium and potassium in the blood. A small gland within the brain called the pituitary gland samples the blood with its osmoreceptors. If there are ample concentrations of solutes in the blood, the osmoreceptors are activated and then instruct the pituitary to release ADH. ADH travels to the kidneys where it binds to receptors, instructing cells of the kidney collecting ducts to create aquaporins. Aquaporins are small channels which allow the reabsorption of water back into the blood, essentially concentrating urine. When osmoreceptors in the pituitary detect low levels of solutes in the blood, the release of ADH is suppressed, causing less water to be reabsorbed and therefore more urine to be created.
Two Types of Diabetes Insipidus
There are two types of diabetes insipidus (DI) caused by two separate things. Central DI occurs when the pituitary doesn't produce ADH, often from the result of trauma to the brain or the growth of a tumor on the pituitary. Some cases of central DI are considered idiopathic, meaning they have no known cause. Nephrogenic DI results when the kidneys don't properly respond to ADH. This form of DI can be caused by congenital defect, drugs, or metabolic disorder. When caused by congenital defect, nephrogenic DI is more much likely to be a hereditary condition. For this reason, dogs with this condition should not be bred.
Symptoms of Canine DI
Dogs with either form of DI have a nearly insatiable urge to drink and urinate at least every couple hours. Central DI, based on its cause (cancer, trauma) can exhibit neurological symptoms such as stupor, disorientation, and seizures.
Diagnosing Canine DI
Diagnosis can be difficult due to the fact that excessive thirst and urination can be caused by many disorders including hyperadenocorticism, diabetes mellitus, renal failure, liver disease, uterus infection, etc. Veterinarians will commonly take images of the pituitary to determine the presence of a tumor. If no tumor is found, the next option is to inject the dog with artificial ADH and measure the kidneys response.
Treating Dogs with DI
Drug therapy for canine DI isn't a requirement. As long as dogs with this condition have an endless supply of water and an environment where excessive urination isn't a problem, most dogs will do just fine. It is also a good idea to limit a dog's salt intake, as salt causes increased urination. Pets with diabetes insipidus with have drastically altered lives but can live happily and healthy with a little help from their owners.
Photo Credit: Mr. T in DC