Natriuretic hormones
[Ref:WG21:p464-466]
3 types
- Atrial natriuretic peptide
* 28 amino acid residue
- Brain natriuretic peptide
* 32 amino acid residue
- C-type natriuretic peptide
* Mainly paracrinal
Production
Source --> Heart
BNP is also found is brain
* But level is higher in heart
Secretion is proportional to stretching of atria by central venous pressure
Regulation of production
ANP secretion increased when:
- ECF volume is increased
* By high-salt diet, OR
* Infusion of isotonic saline
- Immersion in water
* Immersion also decrease renin and aldosterone
Decreased when:
- Rising from supine to standing
- IPPV, which causes decreased atrial distension
--> Sodium retention in ventilated patients
Detector: stretching of atria
Effect of ANP and BNP
[WG21:p465]
Act on kidney to increase sodium excretion
Mechanism of natriuretic effect
- Vasodilation of afferent arterioles
--> Increases GFR
- Relaxation of mesangial cells
--> Increases GFR
- Directly inhibit sodium reabsorption by renal tubules
* [AV6:p118] Acts on medullary collecting duct
Other effects
- Increase capillary permeability
--> Extravasation of fluid
--> Decrease in BP
- Relaxation of vascular smooth muscles in arterioles and venules
* Counteract the pressor effect of catecholamines and angiotensin II
- Inhibit renin secretion
- Reduce responsiveness of zona glomerulosa to angiotensin II
[WG21:p383]