Disorders of Vasopressin

Question 1

What is another name for vasopressin?

Answer 1

ADH

Question 2

Main function of vasopressin?

Answer 2

stimulates reabsorption via aquaporins in the DCT/ collecting duct

Question 3

Vasopressin is released via?

Answer 3

posterior pituitary

Question 4

How is the posterior pituitary related to the hypothalamus?

Answer 4

anatomically continuous

Question 5

Vasopressin acts to reabsorb water via what receptor?

Answer 5

V2

Question 6

Name a secondary physiological action of vasopressin and via what receptor?

Answer 6

acts as a vasoconstrictor

via V1 receptor

Question 7

Vasopressin can stimulate what hormone release?

Answer 7

ACTH from the anterior pituitary

Question 8

Explain how vasopressin concentrates urine.

Answer 8

AVP binds to V2 receptor > G protein receptor upregulates adenylate cyclase > upregulates cAMP > upregulates pkA > triggers aquaporins > reabsorb water

Question 9

What does a posterior pituitary look like on MRI?

Answer 9

bright spot

absence may be a normal variant

Question 10

List two stimuli for vasopressin. How are the stimuli sensed?

Answer 10

osmotic: rise in plasma osmolality, sensed by osmoreceptors

non osmotic: decrease in atrial pressure sensed by atrial stretch receptors

Question 11

Where does osmotic stimulation of vasopressin release occur?

Answer 11

organum vasculosum + subfornical organ (both nuclei sit around 3rd ventricle)

Question 12

How is the organum vasculosum/ subfornical organ adapted for stimulation of vasopressin?

Answer 12

no blood brain barrier (can respond to change in systemic circulation)
highly vascularised
neurons project into supraoptic nucleus

Question 13

If there is an increase in extracellular Na+, how to osmoreceptors react?

Answer 13

water moves out > osmoreceptor shrinks > increased osmoreceptor firing > AVP release from hypothalamixc neurons

Question 14

Describe non-osmotic stimulation of vasopressin release.

Answer 14

atrial stretch receptors detect pressure in RA > inhibit vasopressin release via vagal afferents

Question 15

Following a haemorrhage, what is the effect on vasopressin release?

Answer 15

haemorrhage = reduction in circulating volume > less stretch of atrial receptors > less inhibtion of vasopressin

Question 16

Describe the physiological response to water deprivation.

Answer 16

^ plasma osmolality > stim. osmoreceptors > thirst/increases AVP release > ^H20 reabsorption > reduced urine volume/increase urine osmolality > reduced plasma osmolality

Question 17

List symptoms of diabetes insipidus.

Answer 17

polyuria
nocturia
extreme thirst
polydipsia

Question 18

What causes diabetes insipidus?

Answer 18

problem with arginine vasopressin

Question 19

Name two types of diabetes insipidus.

Answer 19

cranial

nephrogenic

Question 20

What is cranial diabetes insipidus?

Answer 20

problem w/ hypothalamus/posterior pituitary

unable to make AVP

Question 21

What is nephrogenic diabetes?

Answer 21

manufacture of AVP is normal

collecting duct unable to respond to it

Question 22

Causes of diabetes insipidus are grouped into? Which is rare and which is common?

Answer 22

Acquired (common)

Congenital (rare)

Question 23

List acquired causes of cranial diabetes insipidus.

Answer 23

traumatic brain injury
pituitary surgery
pituitary tumours/metastasis to pituitary
autoimmunity
granulomatous infiltration of pituitary stalk e.g. TB, sarcoidosis

Question 24

List causes of nephrogenic diabetes insipidus.

Answer 24

mutation in gene encoding V2 receptor
mutation in gene encoding aquaporin 2
drugs e.g. lithium

Question 25

What is psychogenic polydipsia?

Answer 25

patient drinks too much water so passes large volume of water (mimics diabetes insipidus)

Question 26

What test can you administer to distinguish between diabetes insipidus and psychogenic polydipsia? What does this test measure?

Answer 26

water deprivation test (no water access, measure urine volume/concentration and plasma osmolality)

Question 27

Compare the results between a diabetes insipidus and psychogenic polydipsia water deprivation test.

Answer 27

psychogenic polydipsia is normal, urine is more concentrated less volume
diabetes insipidus would remain the same

Question 28

What marker indicates you should stop the test?

Answer 28

lost >3% of body weight (significant dehydration)

Question 29

How do you distinguish between cranial and nephrogenic diabetes insipidus?

Answer 29

give ddAVP
CDI responds and urine concentrates
NDI can’t respond urine remains the same

Question 30

How do you treat cranial diabetes insipidus?

Answer 30

replace vasopressin
desmospressin nasal spray/tablets
selective for V2 receptors

Question 31

How do you treat nephrogenic diabetes insipidus?

Answer 31

thiazide diuretics e.g. bendofluazide

paradoxical/mechanism unclear?

Question 32

What is SIADH?

Answer 32

syndrome of inappropriate ADH

too much AVP

Question 33

List causes of SIADH.

Answer 33

CNS (head injury/stroke)
pulmonary (pneumonia)
malignancy (lung cancer/CNS tumour)
drug related (SSSRI, carbamezapine)
idiopathic

Question 34

SIADH causes what symptoms?

Answer 34

concentrated urine
low plasma osmolality
hyponatraemia

Question 35

When does fasting blood glucose indicate diabetes mellitus?

Answer 35

> 7mmol/litre

Question 36

When does random blood glucose indicate diabetes mellitus?

Answer 36

> 11mmol/litre

Question 37

What basic test helps indicate diabetes insipidus?

Answer 37

sodium levels

high Na+ indicates dehydration

Question 38

How to treat SIADH

Answer 38

Vaptan