The Action of Aldosterone on Sodium Transport: Further Studies with Inhibitors of RNA and Protein Synthesis1

Abstract

In the isolated toad bladder, addition of actinomycin D to the medium, either IS, 30 or 60 min after aldosterone attenuated the response to the hormone but did not alter the duration of the latent period. The initial rate of rise in Na⁺ transport and the magnitude of the peak varied with the time of exposure to aldosterone without inhibitor. The peak of the response was attained ISO min after addition of aldosterone regardless of the time of introduction of actinomycin D. Addition of cycloheximide 15 min before aldosterone and removal of the inhibitor 60 min after aldosterone had little effect on the timecourse or magnitude of the increase in Na⁺ transport. Addition of cycloheximide 90 min after aldosterone arrested the increase in Na⁺ transport; removal of the inhibitor 75 min later, evoked an accelerated rise in Na⁺ transport, which was unaffected by either removal of aldosterone or addition of actinomycin D. In aldosterone pre—induced bladders, actinomycin D did not “ super—induce.” Sodium transport declined exponentially either after removal of aldosterone, or addition of cycloheximide or actinomycin D. The inhibitor—mediated declines in Na⁺ transport were uninfluenced by the presence of aldosterone in the media. These results favor the hypothesis of induction at the transcriptional level. (Endocrinology92: 1685, 1973)