Mechanism of the redistribution of renal cortical blood flow during hemorrhagic hypotension in the dog

Studies were performed to define the mechanisms involved in the redistribution of renal cortical blood flow to inner cortical nephrons which occurs during hemorrhagic hypotension in the dog. The radioactive microsphere method was utilized to measure regional blood flow in the renal cortex. Renal nerve stimulation decreased renal blood flow 40% but had no effect on the fractional distribution of cortical blood flow. Pretreatment with phenoxybenzamine, phentolamine, propranolol, or atropine did not alter the redistribution of cortical flow during hemorrhage. A reduction in renal perfusion pressure by aortic constriction caused a qualitatively similar alteration in regional blood flow distribution as occurred during hemorrhage. When perfusion pressure was kept constant in one kidney by aortic constriction followed by hemorrhage, no redistribution occurred in the kidney with a constant perfusion pressure while the contralateral kidney with the normal perfusion pressure before hemorrhage had a marked increase in the fractional distribution of cortical flow to inner cortical nephrons. Additionally, retransfusion had no effect on the fractional distribution of flow in the kidney in which perfusion pressure was maintained at the same level as during hemorrhage while in the contralateral kidney in which pressure increased to normal there was a redistribution of flow to outer cortical nephrons. These studies indicate that the redistribution of renal cortical blood flow which occurs during hemorrhage is not related to changes in adrenergic activity but rather to the intrarenal alterations which attend a diminution in perfusion pressure.