Posterior Pituitary

Question 1

You suspect diabetes insipidus in a pt.

1. what test to confirm diabetes insipidus
2. what test to identify what type of diabetes insipidus

Answer 1

1. water deprivation test–deprive pt of water and see if urine stays dilute. (If urine stays dilute, yes–diabetes insipidus)
2. desmopressin test–give pt desmopressin (ADH analogue) and see if urine is concentrated. (If urine concentrated, then central DI)

Question 2

What does the posterior pituitary gland secrete? (2)

Where specific areas are each of these hormones created?

Answer 2

1. ADH (vasopressin)–made in the supraoptic nucleus of the hypothalamus
2. Oxytocin–made in paraventricular nucleus of hypothalamus
   - Remember–post pituitary hormones are made in the hypothalamus and travel along neuron axons via the infundibulum to the post pituitary, where they are secreted.

Question 3

Nephrogenic diabetes insipidus

-Tx drugs (2 categories)

Answer 3

1. thiazide diuretic–pt’s serum is hyperosmolar, so the only way to correct is excrete those osmotic particles. Of course, rehydrate pt to prevent dehydration.
2. NSAIDs
   - inhibit renal prostaglandins, which interfere with ADH
   - Note: some pts may have limited response to desmopressin

Question 4

Central diabetes insipidus

-Tx

Answer 4

• Desmopressin (ADH analog)
• comes in nasal spray

Question 4

Demeclocycline

• mech
• tx what?

Answer 4

• used to treat SIADH. Not used much anymore b/c of newer ADH blockers (conivaptan, talvaptan)
• mech: blocks nephron response to ADH

Question 5

Nephrogenic diabetes insipidus

-first line tx before trying drugs

Answer 5

remember pt’s blood is hyperosmolar

-Low salt, low protein diet

(limit solute intake. If not effective, then you must excrete solute with thiazide diuretics)

Question 6

SIADH tx drugs

(3 categories)

Answer 6

1. ADH receptor antagonists (conivaptan, talvaptan)
   - block V2 receptors in collecting ducts, decreasing aquaporins
2. Loop diuretics (furosemide, bumetanide)
   - increase free water excretion
3. Demeclocycline (inhibits collect duct responsiveness to ADH. not used much anymore)

Question 7

How do loop diuretics help pt with SIADH?

-name the 2 bolded loop diuretics

Answer 7

Pt is hyponatremic, so flush out all that dilute water

• furosemide, bumetanide

Question 8

ADH functions (2)

Answer 8

1. V2 receptor in nephron collecting duct–increase aquaporins on luminal surface to increase water reabsorption. (Gs, cAMP)
2. V1 receptor: vasoconstriction of vascular smooth muscle. (Gq, IP3)

Question 9

Central diabetes insipidus

-causes include: (5)

Answer 9

• Pituitary damage:
  1. autoimmune injury to hypothalamus/pituitary
  2. head trauma
  3. cerebral hypoperfusion
  4. tumors (eg pituitary)
  5. infiltrative disorders–eg sarcoidosis

Question 10

Nephrogenic diabetes insipidus

-causes include (5)

Answer 10

• renal ADH resistance
  1. X-linked recessive disorders
  2. hypokalemia
  3. hypercalcemia (Ca+ deposition can reduce ADH sensitivity)
  4. Renal diseases
  5. drugs (classically Lithium)

Question 12

SIADH

-clinical symptoms (2)

Answer 12

1. reduced urination–causes hyponatremia, low serum osmolality
2. seizures, mental status changes–hyponatremia causes intracerebral swelling

Question 13

Conivaptan, Talvaptan

Answer 13

ADH V2 receptor blockers

• block V2 receptors in collecting ducts, decreasing aquaporins. This allows more free water excretion.
• used to tx SIADH

Question 14

Pt with SIADH:

-first line treatment, before trying drugs

Answer 14

Pt is hyponatremic.

1. free water restriction
2. IV salt solution