Mechanism of excretion of radioiodinated sodium iothalamate.

Abstract

Sodium iothalamate (Conray), a triiodinated benzoic acid derivative, originally was prepared as a contrast medium for angiography and excretory urography (1). Recently Sigman et al. have shown that the simultaneous renal clearance of 131I sodium iothalamate and inulin in man were essentially the same (2, 3), and glomerular filtration rate (GFR) was determined rapidly and simply by counting plasma and urine radioactivity. It is likely that iothalamate is excreted primarily by glomerular filtration, although a fortuitous combination of filtration plus tubular secretion and reabsorption could explain these results. Because of the practical advantages in using radioiothalamate as an inulin substitute, additional studies of the mechanism of its excretion have been carried out with the aglomerular fish and the dog as experimental models. These results support the concept that iothalamate is excreted only by glomerular filtration. Materials and Methods Sodium iothalamate labeled with 131I or 125I was obtained fr...