[Effects of a non-ionic low osmolar contrast medium on thyroidal radioiodine uptake in rats]

Recently non ionic low osmolar contrast media (NILOCM) have been widely used in radiographic contrast studies. These new agents have a great advantage over conventional ionic high osmolar contrast media (IHOCM) in low chemical toxicity and good X-ray absorption. However, their effects on thyroid function, especially on thyroidal radioiodine uptake (TRIU), are still unknown and it is not clear how long NILOCM interfere with TRIU. Therefore, the extent of the interference with TRIU caused by previous NILOCM injection was examined using rat thyroid. Male WKA rats were divided into four groups and fed under different dietary conditions, A) routine diet for rats; B) low iodine diet (LID) for 1 week, C) LID for 2 weeks, and D) LID for 8 weeks. Iopamidol was used as NILOCM, and iothalmate, one of IHOCM, was also employed for comparative study. After feeding, some rats in each group were injected with 300 mgI/kg. b.w. of iopamidol or iothalmate. The remaining rats in each group received saline injection as the control. At day 1, 2, 3, 7, and 14 following injection, I-131 was administered intravenously and a 24 hour TRIU (% dose/mg tissue) was measured in each group. Thyroidal iodine content (TIC: micrograms I/mg tissue) at day 1, 7, and 14 was also measured in group A, C, and D. Until day 3, severe suppression on TRIU was observed in all groups, and TIC elevated at day 1 in iothalmate-injected rats. In iopamidol-injected rats, TRIU and TIC recovered after then, and reached the same levels as those in control rats until day 14 except for group D. However, TRIU was still significantly lower and TIC levels in group D was higher at day 14 in iothalmate-injected rats. It is concluded that iopamidol has less effects on TRIU and TIC with a shorter period of recovery than iothalmate. This results maybe beneficial to the patients who were injected NILOCM prior to radioiodine scintigraphy.