The Journal of clinical investigation
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Distribution of intrarenal blood flow was studied in 12 dogs anesthetized with Nembutal. Medullary blood flow was estimated by local clearance of hydrogen gas from the outer medulla measured polarographically with needleshaped platinum electrodes, and by local clearance of (85)Kr and mean transit time of (32)P-labeled erythrocytes measured with a small semiconductor detector placed in the outer medulla. Cortical blood flow was estimated from cortical red cell transit time and from total renal blood flow measured by electromagnetic flowmeter. ⋯ Reinfusion of blood after 2-3 hr of hypotension increased total renal blood flow to an average of 82% and outer medullary hydrogen clearance to an average of 92% of control values. All dogs survived the experiment without evidence of renal failure. It is concluded that hemorrhagic hypotension in dogs leads to a progressive and fairly uniform rise in renal vascular resistance, without any selective hemodynamic response in the juxtamedullary circulation.
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The importance of plasma protein concentration, renal vascular resistance, and arterial pressure as mediators of the natriuretic response to volume expansion was investigated in anesthetized dogs. Saline loading depressed plasma protein concentration and increased arterial pressure but did not decrease renal vascular resistance. Restoring plasma protein concentration by infusing hyperoncotic albumin increased sodium reabsorption and decreased sodium excretion during saline loading despite simultaneous decreases in renal vascular resistance and increases in arterial pressure. ⋯ However, in kidneys vasodilated before infusing blood sodium excretion increased in response to the infusion in association with increased arterial pressure. This increased excretion of sodium by vasodilated kidneys during infusion of blood could be abolished by reducing perfusion pressure to the preloading level. These observations indicate that changes in plasma oncotic pressure, renal vascular resistance, and arterial pressure either alone or in combination are important variables determining the natriuretic response to volume expansion, and that the relative importance of each of these factors depends on the manner in which volume is expanded (viz., the infusion of saline, plasma, or blood).