Red cell trapping and postischemic renal blood flow. Differences between the cortex, outer and inner medulla

Area of Science:

• Nephrology
• Physiology
• Cardiovascular Research

Background:

• Renal ischemia can lead to significant alterations in intrarenal blood flow distribution.
• Understanding these changes is crucial for developing therapeutic strategies to protect kidney function during ischemic events.

Purpose of the Study:

• To investigate the role of red blood cell (RBC) trapping in the redistribution of renal blood flow following ischemia.
• To determine the impact of reduced hematocrit on blood flow dynamics in different kidney regions after ischemic injury.

Main Methods:

• Single-fiber laser-Doppler flowmetry was used to measure blood flow in the superficial cortex, outer medulla, and inner medulla of rat kidneys.
• Red blood cell volume was manipulated using isovolemic hemodilution to assess its effect on blood flow distribution.
• Radiolabeled RBCs were used to quantify fractional RBC volume in kidney tissue.

Main Results:

• Renal ischemia caused a significant decrease in superficial cortical and outer medullary blood flow, while inner medullary flow paradoxically increased.
• Extensive trapping of RBCs was observed in the outer medulla, with fractional RBC volume increasing from 2% to 21%.
• Reducing hematocrit before ischemia abolished RBC trapping and preserved outer and inner medullary blood flow, although superficial cortical flow still decreased.

Conclusions:

• RBC trapping in the outer medulla is a key factor in reducing outer medullary blood flow and shunting blood to the inner medulla post-ischemia.
• Preservation of medullary blood flow after ischemia can be achieved by preventing RBC trapping through hemodilution.