Effects of Triamterene and Its Phase I and Phase II Metabolites on Sodium Transport of the Isolated Frog Skin

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Abstract
The effects of triamterene (TA), a K+-sparing diuretic, and its phase I and phase II metabolites, p-hydroxytriamterene (OH-TA) and p-hydroxytriamterene sulfuric acid ester (OH-TA ester), on Na+ transport in the isolated frog skin were studied. TA applied to the inside (corial side) surface had no effects on the potential difference (PD) and short-circuit current (SCC) while, TA, OH-TA, and OH-TA ester at a concentration of 10-5 mol/l significantly decreased SCC by 19, 24 and 16%, respectively when added to the solution bathing the outside (epithelial side) surface of the skin. In vasopressin-treated skins TA was more effective than OH-TA or OH-TA ester. In aldosterone-treated skins all compounds significantly suppressed SCC; the strongest effect was again exerted by TA. Only minor and transient changes in PD were noted. Inhibition of Na+ transport was rapidly reversible when skins were washed with fresh Ringer solution. Thus, OH-TA and OH-TA ester possess qualitatively similar pharmacological activity as TA. The quantitatively smaller effects of OH-TA and OH-TA ester in the hormone-stimulated skin as compared to TA agrees well with their relative natriuretic potency observed in vivo.