Renal Medullary Countercurrent System Studied with Hydrogen Gas

Abstract

The renal countercurrent exchange mechanism was studied by recording the removal of hydrogen gas from the medulla of dogs. Hydrogen was administered by respiration or by intra-arterial infusion of hydrogen-saturated saline. Simultaneous desaturation curves were recorded polarographically by means of two or three needle-shaped platinum electrodes inserted into various positions in the medulla. It was found that the desaturation rate in the inner medulla was mainly dependent on urine flow, in such a way that the fractional rate of removal increased from 0.05 to 0.75 min -1 when urine flow was raised from 0.1 to 5 cc/min/kidney. Saline, mannitol and water diuresis had the same effect. On the basis of pelvic urine desaturation curves, which were practically identical to desaturation curves from the tip of the papilla, it was calculated that as much as two-thirds of the medullary hydrogen content may be removed by urine. The clearance rate was higher in the outer medulla and less dependent on urine flow. No consistent correlation with effective renal blood flow could be demonstrated in any segment of the medulla. The results indicate a very high efficiency of the countercurrent exchange mechanism with respect to hydrogen, and recordings from the corticomedullary border gave direct evidence for a high degree of hydrogen shunting across the vessel loops. Physiological implications of the findings with respect to oxygen and sodium chloride are discussed.