What is diabetes insipidus?

When we think of diabetes, it is probably about diabetes mellitus, which is all about the elevated glucose level in blood plasma. We all know this already. So how about diabetes insipidus?

Few centuries ago, physicians tasted urine from patients to diagnose disease; if it is sweet, they suspect diabetes mellitus, and if it is flavorless, it is diabetes insipidus.

Diabetes insipidus results in excessive thirst and urination, and the etiology of this condition is by complications related to vasopressin, also known as antidiuretic hormone (ADH), which is produced by hypothalamus, and stored in posterior pituitary gland. This hormone is released when there is a decrease in blood pressure, and its release causes kidneys to reabsorb water to maintain homeostatic balance in blood pressure. Ultimately, this leads into highly concentrated urine production.

Simply, the symptoms of diabetes insipidus are characterized by polydipsia, drinking a lot of water, and polyuria, excreting a lot of water in urine; these obviously lead into dehydration, sometimes at severe degree. The excessive dehydration may also cause imbalances in electrolyte. This disease is caused by either vasopressin-insufficiency or vasopressin-insensitivity, which is quite similar to the cause of the pathogenic conditions observed in diabetes mellitus. In both cases, the kidneys cannot reabsorb water, and the water is excreted as urine.

The most important aspect in treating diabetes insipidus is to drink a lot of water because it replaces the constant loss of water by urination. If the disease is caused by vasopressin-deficiency, then the low level of vasopressin can be handled by taking vasopressin supplementary medication, orally or nasally. If diabetes insipidus is caused by vasopressin-insensitivity, then it gets a bit complicated to deal with it. Surprisingly, the vasopressin-insensitivity condition is treated with a diuretic; taking diuretic hydrochlorothiazide decreases reabsorption of water and sodium in distal convulated tubule, which eventually causes dieresis. Therefore, the overall plasma volume gets decreased, and thereby, decreasing in glomerular filtration rate (GFR) and enhancing the absorption of water and sodium in proximal convulated tubule. Ultimately, this results in conservation of plasma fluid volume.

 

Diabetes insipidus is not complicated with fatal pathogenesis, and the kidneys are still functional in the sense of blood filtration. However, it is still a disease, which causes dehydration, sometimes at severe degree, and the people, who are afflicted with diabetes insipidus, require constant fluid consumption. The urinary system plays a crucial role in homeostatic maintenance of fluid balance.

References:

Loffing J. 2004. Paradoxical antidiuretic effect of thiazides in diabetes insipidus: another piece in the puzzle.” J. Am. Soc. Nephrol. 15 (11): 2948-50.