Week 1 Vasopressin Disorders Flashcards
What are the three types of vasopressin disorders?
- Deficient
- Resistant
- Excessive
Where is vasopressin produced?
Produced in the hypothalamus
Released from posterior pituitary
How do you test for someone’s first response?
Give IV saline and then see how thirsty they are
What signal best represents vasopressin release?
Copeptin.
This is on of the amino acids that make up vasopressin
How do you treat vasopressin insufficiency?
Desmopressin
Has a longer half life than indogenous vasopressin and also selectively targets receptors in the kidney so doesn’t contribute to vasoconstriction.
What are the main vasopressin receptors?
What vasopressin receptor has a higher afinity for vasopressin?
V2 > V1
The kidney ones are more responsive to vasopressin than the CV receptors which only kick in in very high amounts of vasopressin
What non-osmotic stimuli can affect vasopressin release?
- Peripheral stimuli-
- Low Blood pressure,
- Low ECF Volume
- Pain
- Nausea
What is the main stimulus that can affect vasopressin release?
Osmolality
What would be the investigation steps into polyuria?
Think about distinguishing between these symptoms
Causes
(I) Vasopressin Deficiency/Resistance
(ii) Primary polydipsia
(iii) Osmotic diuresis: glucose, etc…
(iv) Renal impairment
(1) accurate fluid balance & plasma [Na+] : determine if polyuria
* Urine volume >2ml/kg/hr
* Urine volume high and persistent thirst or [Na]conc > 145mmol/l (if serum sodium is normal/ low this would probably be primary polydipsia)
(2) check glucose, urea, eGFR, K+, Ca2+ - identify cases of (iii) & (iv)
(3) check urine never normally concentrated
* random urine samples
* early morning urine
* if >600mosmol/kg then excludes VpD/VpR
(4) water deprivation test –negative water balance
Show if unable to concentrate urine = Vp disorder (VpD/VpR)
(5) Give DDAVP (2µg IM) to diagnose VpD or VpR
- If πu rises so > 600mosmol/kg, or >50% = VpD
- If no such effect (πu still < 600) = VpR
What are the signs of polyuria?
High urine volume and high serum Na concentration
What is DDAVP
Desmopressin
How would giving desmopressin distinguish between VpD and VpR?
Perform water deprivation test.
If urine osmalality of urine remains low then that is confirmation of VpD/VpR and not primary polydipsia.
Give desmopressin.
If urine osmalality increases then VpD.
If urine osmalality remains low then VpR
Draw out a summary of the results of a water deprivation test
What is primary polydipsia?
Psychogenic polydipsia
What is a convenient way to distinguish between VpR/VpD/Primary Polydipsia without going through a water deprivation test?
Look for serum copeptin.
If low would be VpD or primary polydipsia.
If high implies VpR
Then give hypertonic saline IV and check for copeptin again. If it goes up it is primary polydipsia but if it stays the same it’s VpD
Why is polyuria combined with serum sodium alone not enough to tell between primary polydipsia and VpD/VpR?
If urine osmalality is low and serum Na high this is likely VpD/VpR
However if urine osmalality is low and serum Na is normal this could still be VpD/VpR along with primary polydipsia particularly if VpD/VpR is early or mild
What causes vasopressin deficiency?
- Neurosurgery
- Any pituitary disorders
- Major haemorrhage
- Head injury
- Idiopathic
- Isolated gene - VP gene
- Wolfram Syndrome
- Pregnancy
How does Wolfman syndrome present?
Diabetes Insipidus (VpD), Diabetes Mellitus, Optic Atrophy, Deafness
Causes of vasopressin resistance?
hypercalcaemia
hypokalaemia
resolution after urinary tract obstructive
secondary effect of psychogenic polydipsia
Lithium therapy effect
Demeclocycline
Inherited
majority V2R X-linked,
others AQP2 Ch12 – A.Recessive or A.Dom
What is the investigative summary for water retention?
Draw it out.
Think serum sodium, dehydration, urine sodium, oedema, urine osmolality.
What does SIADH stand for?
Syndrome of inappropriate antidiuretic hormone secretion
Causes of SIADH?
Intracranial Lesions/disease - of diverse kinds
Intrathoracic disease, especially infections
Neoplasms, especially lung/mediastinal
Drugs
antipsychotics
sedatives
SIADH Treatment
Restrict fluid intake
Increase solutes
If urgent to moderate hyponatraemia consider IV saline but…
Must normalise chronic hyponatraemia slowly ([Na+] < 8-10mmol/l/day)
New options - vasopressin-antagonists: ‘vaptans’
- aquaretics – V2 receptor antagonists e.g. Tolvaptan
- combined V2-V1a antagonists e.g. conivaptan
