Increased activity of enzymes of the tricarboxylic acid cycle in response to aldosterone in the toad bladder

Summary

1. The activities of condensing enzyme, isocitrate dehydrogenase, glutamate dehydrogenase, glutamate-oxaloacetate transaminase, and malate dehydrogenase increase in toad bladder mucosa in vitro 2 hours after addition of d-aldosterone (10⁻⁷ M) to the serosal bathing medium whereas no change in activity of lactate dehydrogenase, aldolase and pyruvate kinase was noted.

2. The increase in enzyme activities has approximately the same time course as the stimulation of sodium transport by aldosterone.

3. The response of sodium transport to d-aldosterone was studied in the same tissue which was assayed for enzymatic activity. A significant, positive correlation between relative increments in sodium transport and in condensing enzyme activity per milligram of mucosal protein was found to exist.

4. The effects of aldosterone on both sodium transport and enzyme enhancement were abolished by actinomycin D and puromycin.

5. The increase in activity of mitochondrial enzymes due to d-aldosterone was not dependent on the presence of sodium in the mucosal bathing medium and hence was independent of any possible direct stimulatory effect of transepithelial sodium transport on enzyme activity.

6. The increase in activity of enzymes contributing to the supply of aerobic energy for the enhanced sodium transport induced by aldosterone is regarded as complementary to an independent action of the hormone to increase the entry of sodium into the transport process.