1. Isolated dogs' kidneys have been perfused with defibrinated blood under hemodynamic conditions similar to those in the body. Under these circumstances blood flow, urine secretion, and oxygen consumption are well maintained, but urea clearance is low. Renal venous blood collected initially and at the end of 3 or more hours of perfusion exhibited no difference in vasoconstriction properties when perfused along with renin or renin-activator through an isolated rabbit's ear.

2. Reduction of pulse pressure by constricting the renal artery may be performed without reducing mean pressure significantly. Impairment of urea clearance and rate of urine secretion follow, and oxygen consumption is slightly reduced.

3. After an hour or more of perfusion with reduced pulse pressure, gradual rise in mean renal arterial pressure distal to the clamp and reduction of blood flow occur.

4. Renal venous blood collected after about one hour of perfusion with reduced pulse pressure differs from that collected before reduction of pulse pressure in that it causes intense vasoconstriction when perfused with renin-activator through an isolated rabbit's ear.

5. Perfusion of a dog's hind leg under similar circumstances does not cause this change in the venous blood to occur.

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