Aldosterone chemical structure

In the foregoing paragraphs, the activity of a number of classes of diuretic substances which block sodium transport in the kidney distal tubule has been discussed. It remains to examine these structures to assess whether or not a particular chemical grouping is responsible for this activity. Mechanisms of action of diuretics are difficult to examine on the kidney itself but it is fortunate that there are a number of model epithelia which behave very similarly to the distal tubule. For example, amphibian skins and bladders [179,180] actively transport sodium from the mucosal to the serosal side by an active transport process. These epithelia respond to aldosterone with an increase in sodium transport [181] and furthermore, under appropriate conditions they can be made to acidify the mucosal solution [182]. Amphibian epithelia, therefore, provide ideal systems for examining the actions of diuretics which act on the distal tubule. 

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