Diabetes insipidus is a very rare disease in which there is an inadequate amount of a hormone called vasopressin in the body, or the kidneys do not respond normally to vasopressin. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) states that the main symptom of diabetes insipidus is frequent urination. There are several different causes of the disease, which target different components of the signaling pathway between the pituitary gland and the kidneys.
Pituitary Gland Damage
The most common cause of diabetes insipidus is a damaged pituitary gland, according to the NIDDK. Normally, the pituitary gland signals to another gland called the hypothalamus to secrete the hormone vasopressin. Vasopressin then acts on the kidneys and signals them to retain fluid. However, a damaged pituitary gland results in an insufficient amount of vasopressin being released from the hypothalamus, and the result is kidneys that excrete too much fluid. Dehydration and an imbalance of electrolytes, which are minerals that are normally present in the blood, then occurs. When the cause is a damaged pituitary gland, the disorder is specifically called central or neurogenic diabetes insipidus. There are many possible causes of damage to the pituitary gland, according to the Diabetes Insipidus Foundation, which include cancer, infection, congenital or inherited diseases, and trauma to the head. Often the reason is "idiopathic," meaning doctors can find no known cause of the damage.
A Kidney Defect
MedlinePlus, an online medical encyclopedia, states that another cause of diabetes insipidus is a defect in the tubules of the kidneys, which are little structures in the kidney that are responsible for reabsorbing fluid from the blood. The defect makes the kidneys unresponsive to the vasopressin secreted by the hypothalamus. When defective kidney tubules are the cause, the disorder is called nephrogenic diabetes insipidus. In this scenario, the pituitary gland and the hypothalamus function normally, but the kidneys do not respond to the vasopressin signal. Thus, the kidneys excrete too much fluid, causing diabetes insipidus. The causes of defects in the kidneys may be idiopathic, congenital, meaning present at birth, or a result of ingesting toxic substances.
Pregnancy
Another possible cause of diabetes insipidus is the placenta, an organ present in all pregnant mothers. The placenta is attached to both the fetus and the mother, and allows the exchange of oxygen, nutrients, and waste between mother and fetus. Very rarely, the placenta produces a type of protein called an enzyme that destroys vasopressin, according to the NIDDK. The resulting lack of fluid reabsorption by the kidneys then occurs, causing diabetes insipidus. This type of diabetes insipidus, called gestational diabetes, disappears when the woman is no longer pregnant.
