Inhibition of active sodium transport by radiographic contrast media

We demonstrate that salts of diatrizoate and iothalamate, radiographic contrast agents, depress the active transport of sodium in the urinary bladder of the Columbian toad, Bufo marinus. Isolated toad bladders were incubated in isotonic Ringer's solutions with isosmolar displacement of sodium chloride by contrast media in experimental solutions. Sodium transport as measured both by short-circuit current (SCC) and by isotopic sodium flux was significantly depressed in the presence of sodium diatrizoate. Sodium transport measured by SCC was significantly depressed with sodium iothalamate and meglumine iothalamate. Equimolar methylsulfate Ringer's solution did not depress SCC. Although contrast media in isotonic Ringer's solutions depressed basal SCC, the vasopressin-stimulated increment in SCC was not depressed by contrast media. Separate experiments with hyperosmolar solutions (786 mM, as utilized in angiography) demonstrated equivalent suppression of SCC by contrast media and by other solutions made hyperosmolar with glucose or sodium methylsulfate, implying a general or nonspecific effect of hyperosomolarity. Inhibition of SCC by contrast media was reversible when the agents were removed by serial changes with standard Ringer's solution. Inhibition of sodium transport by contrast media might provide a basis for studies on some of the clinical toxicities of these agents.