Cadmium enhancement of proximal tubular sodium reabsorption

¹ Department of Physiology, University of Michigan Medical School, Ann Arbor, Michigan

Stop-flow studies were performed to localize the site of cadmium action on renal sodium reabsorption. In the untreated dog undergoing mannitol diuresis, a maximal lumen:plasma sodium gradient was established across the proximal tubule during free flow with no further lowering of luminal concentration during ureteral occlusion, Na_prox/Na_FF = 1.02 ± .05. During occlusions after cadmium, sodium concentrations in proximally trapped fluid were reduced below free-flow values, Na_prox/Na_FF = 0.85 ± .08. This difference between treated and untreated animals was statistically significant (P = < .001) and indicates that cadmium enhances proximal sodium reabsorption. Although distal sodium patterns were unaltered by cadmium, it was not possible to rule out a possible distal site since distal sodium reabsorption is already virtually complete during occlusion in the untreated animal. Cadmium, given intravenously as Cd¹¹⁵, was not excreted in the urine.