Pressure natriuresis and diuresis

When renal artery BP INCREASE

--> Reduced number of Na-H antiporter and reduced Na-K ATPase activity in proximal tubule

--> Reduction in sodium resorption in proximal tubule

--> Reduction in water resorption in proximal tubule

Thus,

• Increased sodium excretion
  * i.e. Pressure natriuresis
• Increased water excretion
  * i.e. Pressure diuresis

--> ECF volume decreased

--> Inital BP rise diminished

Other factors

• A small increase in GFR also contribute to natriuresis and diuresis
  * Small because autoregulation (myogenic) blunts increase in GFR due to increase in BP
• Increased BP
  --> Increased peritubular capillary pressure
  --> Increased renal interstitial pressure
  --> Decreased fluid absorption

NB:

• Pressure natriuresis and diuresis occur together
  --> Not able to control sodium and water independently
• Independent of vasomotor activity
• In effect, isotonic urine is excreted to reduce blood volume (though urine not necessarily actually isotonic)

Volume status

The degree of pressure natriuresis and diuresis is dependent on volume status

When ECF volume is high

Increase in renal artery pressure

--> Large pressure natriuresis and diuresis

When ECF volume is low

Increase in renal artery pressure

--> Small pressure natriuresis and diuresis

Angiotensin II and sympathetic activity

When BP increase, both angiotensin II and sympathetic activities decrease.

If these two were kept constant,
--> Pressure natriuresis and diuresis response blunted