Diabetes Insipidus

Question 1

What is ADH?

Answer 1

antidiuretic hormone

Question 2

Where is ADH made? Where is it stored?

Answer 2

ADH is made by the hypothalamus and stored in the posterior pituitary (neurohypophysis).

Question 3

What stimulates the release of ADH?

Answer 3

• osmoreceptors in hypothalamus detect increase in solute concentration
• stretch receptors in blood vessels can stimulate the release of ADH when blood volume decreases
• severe pain, nausea, trauma, surgery and some drugs can stimulate ADH release

Question 4

What is something that may inhibit ADH release?

Answer 4

alcohol

Question 5

What is the action of ADH?

Answer 5

1) bind to V2 receptors in collecting duct of nephrons, causes insertion of aquaporins to increase water reabsorption
2) in high amounts, bind to V1 receptors in smooth muscle in blood vessel, cause vasoconstriction to increase blood pressure

Question 6

What are the two types of diabetes insipidus?

Answer 6

1) neurogenic/central

2) nephrogenic

Question 7

What is the pathophysiology of neurogenic diabetes insipidus?

Answer 7

• deficiency of ADH due to damage to secreting cells
• 80-90% of cells damaged/lost before this problem becomes noticeable
• can occur temporarily from head injury or surgery near hypothalamus

Question 8

What is the pathophysiology of nephrogenic diabetes insipidus?

Answer 8

• decreased response to ADH
• may be from genetic problem
• can also be acquired from drugs or electrolyte imbalances

Question 9

What are the main manifestations of diabetes insipidus?

Answer 9

• large urine output
• excessive thirst
• normally individual drinks a lot (if unable to drink, becomes dehydrated rapidly

Question 10

How is diabetes insipidus diagnosed?

Answer 10

• 24 hour output
• rule out other causes (glucose in urine? kidney disease?)
• measure ADH levels, plasma and urine osmolality before and after a period of fluid deprivation (no change in neurogenic)
• can administer ADH (no response if nephrogenic)
• if neurogenic, MRI to try and determine cause

Question 11

How is diabetes insipidus managed?

Answer 11

• administer ADH (synthetic = desmopressin acetate)
• thiazide diuretics (seems contradictory but works with your body’s response to try and compensate and ultimately can increase sodium and water reabsorption in the kidneys
• in special cases of partial neurogenic diabetes insipidus, the antidiabetic chlorpropamide can be given