by Tarek Musslimani

Created on: June 16, 2009   Last Updated: January 20, 2010

Diabetes insipidus is an endocrine disorder of the pituitary gland. The pituitary gland is a small gland that is located below the hypothalamus at the bottom of the brain. It secretes sever hormones. Five of them are secreted by the anterior part of the pituitary gland and two of them are secreted by the posterior part.

In diabetes insipidus one important hormone of the two that are secreted by the posterior part is called antidiuretic hormone or ADH. An alternative name to this hormone is arginin vasopressin. This hormone is the one that is important for the medical condition of diabetes insipidus.

The secretion of the antidiuretic hormone ie regulated by a negative feedback from the volume of the blood and its osmolality. Hypovolemia condition stimulates the release of antidiuretic hormone from the posterior part of the pituitary gland into the blood circulation. Likewise, high blood osmolality stimulates the release of this hormone from the pituitary gland. Conversely, low osmolality leads to low level of ADH secretion. In the case of hypervolemia also the release of ADH is also stopped.

Antidiuretic hormone is a polypeptide hormone that is composed of ten amino acids that are connected to each other using peptide bonds. It is similar in structure to the other hormone that is secreted by the posterior pituitary gland which is called oxytocin. Oxytocin is unrelated in function to antidiuretic hormone but has a different function related to the contraction of myoepithelial cells of the breast. Thus inducing milk ejection from the breast. In addition to this function, this hormone helps in the contraction of the uterus during child birth.

Diabetes insipidus can be caused or triggered mostly due to a surgery of the pituitary gland. This is so often due to an adenoma of the pituitary gland which oversecretes hormones of various types depending on the part of the pituitary gland that is removed. Removal of the part of the pituitary gland that secretes antidiuretic hormone makes the secretion of this hormone deficient.

The normal functioning of antidiuretic hormone is by stimulation of the nephron tubules to reabsorb more water molecules usually filtered in the glomerulus. Deficiency of this hormone in the blood leads to disturbances of water homeostasis by wasting large quantities of water in the urine. This type of diabetes insipidus is a direct result of the deficiency of antidiuretic hormone. Another type of diabetes insipidus occurs with normal endocrine secretion of antidiuretic hormone. Namely, there is appropriate amount of antidiuretic hormone in the blood. The problem in this case is the lack of sensitivity of the ADH receptors in the nephrons. This type of diabetes insipidus is called nephrogenic diabetes insipidus because it is related to the function of the nephrons of the kidney. Both types of diabetes insipidus lead to excessive losting of water and to dehydration and hypotension.

The treatment to diabetes insipidus depends on the type of disorder the patient has. If the problem is with ADH availability then substitutes in the form of medication solves the problem. If the problem is with nephron malfunction then the water wasted must be compensated by drinking an equivalent amount of water.

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