The contribution of vascular obstruction to the functional defect that follows renal ischemia

Experiments were performed on rats subjected to renal ischemia and various treatment procedures to determine the origin and functional consequences of vascular obstruction. To this end, its occurrence and severity was assessed qualitatively and quantitatively in the outer medulla, where it is particularly prominent. The incidence of medullary hyperemia was not influenced by inhibiting thrombocyte aggregation with 5 or 70 mg/kg of acetyl salicylic acid or preventing fibrin deposition with 100 IE/kg of heparin before ischemia, and these substances produced no improvement renal function. The incidence and degree of hyperemia, however, could be substantially reduced or completely eliminated by acutely raising blood pressure after ischemia or by decreasing the number of circulating erythrocytes before ischemia. These procedures were effective in raising filtration rate and tubular reabsorption from 20% to 60% of normal, in restoring renal blood flow and vascular resistance to completely normal, and in diminishing epithelial damage both three and 18 hours after ischemia. The following conclusions are drawn: first, vascular obstruction, which is not lessened by inhibiting thrombus formation but is easily reversed or prevented by raising perfusion pressure or decreasing hematocrit, is probably caused by erythrocyte aggregation during ischemia. Second, vascular obstruction, which appears to raise renal vascular resistance and lower blood flow and filtration rate, cannot be limited to the medulla but must also be present in the cortex. Finally, reversing or preventing vascular obstruction can fully restore renal perfusion, partially restore glomerular and tubular function, greatly reduce tubular necrosis and thus prevent renal failure.