DECREASED EFFECTIVENESS OF ALDOSTERONE ON ACTIVE SODIUM TRANSPORT BY THE ISOLATED TOAD BLADDER IN THE PRESENCE OF OTHER STEROIDS

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Abstract
Aldosterone can stimulate the active transport of sodium by the isolated toad bladder in vitro. Corticosterone, cortisol, 17[beta]-estradiol and progesterone had no such effect despite incubation of the preparation with more than 100 times the smallest effective concentration of aldosterone. When the serosal surface of the membranes was exposed to 10 [mu]g% d-aldosterone combined with 100 times this concentration of corticosterone, cortisol or progesterone, the stimulating action of aldosterone was reduced. Spirolactone SC 9420 failed to exert by itself a significant effect on the isolated toad bladder in vitro, but this compound blocked the stimulation by aldosterone of active sodium transport in vitro when present at concentration 50 times those of aldosterone. When the concentration ratio was 101, a hormonal effect could be demonstrated, except at the highest concentration of the drug used.