Effects of Cortisol on tubular sodium reabsorption at various sites along the nephron

Abstract

It has been demonstrated that Cortisol increases sodium reabsorption in the proximal tubule, the ascending limb of the loop of Henle and the distal tubule. To make more quantitative analysis, studies were performed in Wister strain rats using the modified technique of “distal blockade ”. By sequentially administering triamterene, chlorothiazide and ethacrynic acid during Mannitol infusion with replacement of urinary losses, increments in sodium excretion were used to calculate sodium reabsorption in the proximal tubule (T_Na prox), in the ascending limb of the loop of Henle (T_Na Henle), at both of the proximal site (T_Na D₁) and the distal site (T_Na D₂) of the distal tubule. On the control experiments, T_Na prox was 41.3±7.7 (Mean±SE) μEq/min; T_Na Henle, 18.0+6.6 μEq min; T_Na D₁, 40. 0±6. 9 μEq/min; T_Na D₂, 16.3±4.3 μEq/min. On the Cortisol administered group, T_Na prox increased to 58.9±3.2 sEq/min (p<0.05), T_Na Henle increased to 37.8±6.6 pEq /min (p<0.05), T_Na D₁ remained at 43.2±6.6 pEq/min and T_N5D₂ increased to 35.1+3.4 μEq/min (p<0.005). In addition, it was shown that there were no alterations in fractional sodium reabsorption rates (% of F_Na) at fhese sites of the nephron. It has been concluded, therefore, that Cortisol enhances sodium reabsorption along all parts of the nephron except D₁ almost uniformly.