Adrenal insufficiency is a disorder in which hormone production by the adrenal glands is impaired. The adrenal glands produce the hormones cortisol, aldosterone, some androgens and the chemical messengers, epinephrine and norepinephrine. Adrenal insufficiency has several causes, including the autoimmune disease, Addison's, tuberculosis, adrenal tumors or tumors in the pituitary gland or hypothalamus; however in most cases the cause of adrenal insufficiency is unknown. The adrenal hormones aldosterone and cortisol are involved in the regulation of blood pressure and water balance.
Diabetes Insipidus
Diabetes insipidus is a condition in which the body no longer maintains water balance. It is caused by a defect in production of the hormone vasopressin or a defect in its target cells in the kidney. The symptoms of diabetes insipidus are excessive urination and extreme thirst. The Mayo Clinic notes people with diabetes insipidus excrete between 2.5 and 15 liters per day, while the normal level of urination is between 1.5 and 2.5 liters per day. Diabetes insipidus is not a common manifestation of adrenal insufficiency, but impairment of aldosterone production can exacerbate diabetes insipidus and decreases in cortisol can actually mask the symptoms of diabetes insipidus.
Urine Output
The maintenance of water balance in the body is a complex process that involves centers in the brain, adrenal glands, kidneys and receptors in arteries. The kidneys detect changes in blood volume. If a low blood volume is detected. the kidneys secrete the enzyme renin, which activates a peptide that stimulates secretion of the hormone aldosterone from cells in the outer adrenal gland. Aldosterone acts on the kidneys and increases reabsorption of sodium and water and increases potassium and hydrogen ion secretion. This increases the volume of fluid in the body and decreases urine output. Another mechanism by which water loss is controlled is receptors in the aorta and hypothalamus detect changes in blood volume and salt concentration, respectively. A signal is transmitted to the pituitary gland to secrete the hormone vasopressin. Vasopressin acts on cells in the kidney to increase water reabsorption from the urine.
Aldosterone Deficiency
If adrenal insufficiency results in low levels of aldosterone secretion, less water is reabsorbed from the urine. In addition to excessive water loss, sodium is lost too causing hyponatremia, potassium is retained causing hyperkalemia and hydrogen ions are retained causing an increase in blood acidity. These electrolyte derangements are common in patients with adrenal insufficiency. People with diabetes insipidus, in contrast, have high levels of sodium in the body, because they have a defect in vasopressin production or action and this hormone reabsorbs water without also reabsorbing electrolytes.
Cortisol Deficiency
A review in the July 2006 issue of the "Journal of the American Society of Nephrology" reports that cortisol insufficiency can mask the symptoms of diabetes insipidus. Cortisol plays a role in maintaining blood pressure and volume. When its levels are decreased, blood pressure decreases, which stimulates the release of vasopressin. Vasopressin, like aldosterone, increases water reabsorption in the kidney. If a person has diabetes insipidus concomitant with adrenal insufficiency and is treated with cortisol the previously masked diabetes insipidus can rapidly manifest.
Treatment
Because these disorders have different causes, a person with them occurring simultaneously will be treated with drugs to treat adrenal insufficiency and drugs to treat diabetes insipidus. Adrenal insufficiency is commonly treated by hormone replacement. Diabetes insipidus is either treated with the synthetic vasopressin, desmopressin or a diuretic that decreases sodium reabsorption.
