Red-cell trapping in the rat renal microcirculation induced by low-osmolar contrast media and mannitol

In acute renal failure after ischemia, intravascular obstruction by trapped red blood cells in the microvasculature of the renal outer medulla is a consistent finding. The influence of intravenously injected contrast media (CM) on such obstruction was investigated.

Anesthetized rats were subjected to 45 minutes of unilateral renal ischemia. Red-cell trapping in ischemically injured kidneys and in the contralateral uninjured kidneys was estimated from the intrarenal distribution of 51Cr-labelled erythrocytes after injection of ioxaglate or iopamidol in a dose of 1,600 mg I/kg body weight. As an osmolar control substance, mannitol (950 mOsm/kg) was given to a third group and isotonic Ringer's solution was administered to a fourth group.

In the uninjured kidneys, treatment with ioxaglate or mannitol resulted in no red-cell trapping, while the iopamidol-treated group showed red-cell trapping in the inner stripe of the outer medulla in a dose-dependent manner. In the ischemically injured kidneys, both CM and mannitol enhanced the red-cell trapping in the inner stripe of the renal medulla.

The results indicate that intravenously administered ioxaglate and iopamidol enhance the microvascular obstructions evoked by ischemic injury and that iopamidol may induce local impairment in renal medullary microcirculation in a normal kidney.