Diabetes insipidus

Question 1

What stimulates the secretion of ADH (vasopressin)?

Answer 1

• Volume contraction causes increased ECF osmolality > stimulates osmoreceptors in the hypothalamus > stimulates ADH secretion
• Hypotension stimulates volume receptors > stimulates ADH secretion

Question 2

What does ADH (vasopressin) do?

Answer 2

• Stimulates the reabsorption of water in the distal tubules and collecting ducts > results in increased water in ECF and decreased ECF osmolality
• Increased ECF osmolality also stimulates the thirst center and increases water uptake > increases water in ECF and decreases ECF osmolality

Question 3

What is used to diagnose diabetes insipidus (differentiate CDI and NDI)?

Answer 3

Natural ADH (pitressin) IM or IV over 1 hour in LRS or 5% dextrose

• Works on both beta-1 and beta-2 receptors

Question 4

Which type of diabetes insipidus is caused by ADH deficiency?

1. Central DI
2. Nephrogenic DI

Answer 4

1. Central DI

Question 5

Which type of diabetes insipidus is caused by impaired responsiveness of the kidney to ADH?

1. Central DI
2. Nephrogenic DI

Answer 5

2. Nephrogenic DI

Question 6

T or F. Diabetes insipidus is associated with polyuria and polydipsia.

Answer 6

True

Question 7

What is the drug of choice to treat central diabetes insipidus in dogs and cats?

1. Desmopressin, DDAVP (1-desamino-8-D-arginine vasopressin)
2. Thiazide diuretics
3. Chlorpropamide

Answer 7

1. Desmopressin, DDAVP (1-desamino-8-D-arginine vasopressin)

• A synthetic ADH analog
• More potent and has a longer duration of action than natural ADH (10-27 hours while ADH has a half-life of only 20 mins)
• Minimal vasoconstrictor action (more selective on V2 than V1)
• Parenterally (SQ, IM, or IV) and nasal drops are instilled into the conjunctival sac

Question 8

What are other treatments, besides desmopressin, for central diabetes insipidus?

Answer 8

• Thiazide diuretics (hydrochlorothiazide, chlorothiazide)
• Chlorpropamide
  
  • Oral hypoglycemic sulfonylurea drug
  • Requires the presence of some endogenous ADH to act
  • Not very effective for treatment of CDI in dogs and cats
• Restricted sodium chloride intake (useful for both CDI & NDI)

Question 9

What is the drug of choice to treat nephrogenic diabetes insipidus?

1. Desmopressin, DDAVP (1-desamino-8-D-arginine vasopressin)
2. Thiazide diuretics
3. Chlorpropamide

Answer 9

2. Thiazide diuretics