Effects of aldosterone on Na transport in the toad bladder I. Glycolysis and lactate production under aerobic conditions

Previous studies indicated that aldosterone enhances active Na⁺ transport, glycolysis, lactate production and respiration of the toad bladder. Evidence was also presented that the changes in glycolysis and lactate production were secondary to the changes in active Na⁺ transport. Further analysis of the relationships between metabolism and Na⁺ transport was undertaken with the aid of two inhibitors of pyruvate metabolism, oxythiamine and phenylpyruvate. These inhibitors prevented the aldosterone-induced increase in oxidation of 6-¹⁴C]glucose but had little effect on the increase in lactate production. In contrast, the effect on Na⁺ transport (i.e., I_sc) was completely inhibited by oxythiamine plus phenylpyruvate with glucose as substrate. The effect on Na⁺ transport, however, was obtained wth the by-pass substrates, oxaloacetate plus ß-hydroxybutyrate, in the presence of these inhibitors. These results implied that steroidal enhancement of lactate production and Na⁺ transport were independent effects. To evaluate whether an increase in Na⁺ transport, per se would augment lactate production, the responses were evaluated under conditions of an imposed Na⁺ gradient (mucosal Na⁺ = 5 mM; serosal Na⁺ = 110 mM). Addition of NaCl to the mucosal media evoked the same increase in I_sc as the addition of aldosterone; both additions increased I_sc more than two-fold. Aldosterone reduced lactate production under these conditions while the re-addition of NaCl had no effect on lactate formation. These results are consistent with an action of aldosterone on pathways involved in oxidative energy metabolism, and suggest that the activation of glycolysis may be a function of the net balance between energy production and utilization.