Failure of iosulamide to enhance hepatic tumors in rats

Iosulamide, an experimental cholangiographic agent recently being evaluated for hepatic contrast enhancement in computed tomography, has been investigated in the rat for the differential enhancement between the liver and three histologically different experimental tumors (a well differentiated mammary adenocarcinoma, a poorly differentiated colon carcinoma, and a hepatoma). After intravenous injection of iosulamide in dosages of 140 and 280 mg iodine per kg, iodine concentrations were determined in blood, liver and tumors at 1, 5, 10, and 30 minutes, using x-ray energy spectrometry. Compared with the surrounding liver parenchyma, the iodine concentrations were generally higher in the breast carcinoma. With respect to the liver, iodine concentrations varied greatly in the colon carcinoma and hepatoma. The iodine washout from all three tumors was relatively slow. Since the distribution volume of cholangiographic contrast agents includes both vascular and interstitial space, the relatively high and prolonged iosulamide accumulation in tumors can be explained by a relatively large interstitial compartment, which is apparently characteristic of neoplastic lesions. This, together with the modest iodine concentrations found in the liver, suggests that iosulamide is of little use in computed tomography for the differential enhancement of liver and hepatic tumors.