Functional capacity of the isolated perfused dog kidney

Summary

1. Vasoconstriction in the isolated kidney can be reduced by the use of fresh blood for perfusion. The amount used for filling the perfusion machine should not exceed that volume which passes the kidney within 3 min. Mechanical stirring and haemolysis should be reduced as much as possible.

2. Initial vasoconstriction is attenuated by addition of dilating drugs to the perfusion system (promethazine, acetylcholine).

3. After a normal period of about 1 hr, total renal blood flow increases to supranormal values as high as 6–10 ml/g · min. It is believed that this dilation is due to liberation of the Hagemann factor in heparinized blood, which activates a bradykinin like substance and to the removal of vasoconstricting factors. Medullary passage times are 40% higher than those obtained in kidneys in situ.

4. Glomerular filtration rate (Creatinine clearance) reaches values (42–86 ml/100 g · min) comparable to those obtained in kidneys in situ. It then decreases during the second phase of the experiment, characterized by increases in total renal blood flow, intratubular pressure, and kidney weight.

5. The isolated kidney reaches a state of water diuresis within 1 hr after transfer to the perfusion system. Urine osmolality falls to values as low as 60 mOsmols/kg with a urine volume of 4 ml/100 g · min.

6. Addition of antidiuretic hormone (0.1–1.0 units/hr) prevents water diuresis but does not maintain a normal concentrating function.

7. In most of the experiments sodium reabsorption is not impaired. Large increases of Na-rejection are observed:

• a) in kidneys taken from dogs having received a high sodium diet for 3 weeks prior to isolation of the kidney.

• b) after infusion of saline either into the animal 1/2 hr before isolation of the kidney (500 ml) or during the perfusion experiment (150 ml).

8. Impairment of Na reabsorption coincides with increased K excretion.

9. It can be stated that the isolated perfused kidney is able to function like a normal kidney in situ. However, there is a progressive impairment of filtration and concentrating processes, for which oedema might be at least partly responsible.