ACUTE EFFECTS OF VARIOUS DOSES OF IODIDE ON THYROID IODINE AUTOREGULATION - A STUDY WITH I-129 BY MEANS OF ANALYTICAL ION MICROSCOPY

Analytical ion microscopy (AIM) was used to determine alterations in the thyroid follicular lumen I-127 stores of Wistar rats injected with different doeses of I-129 (low specific activity radionuclide) Animals fed a normal iodine diet (10-mu-g I-127/d) were divided into four groups: control group and three treated groups injected ip 24 h before sacrifice with I-129 at doses of 10-mu-g (group 1), 30-mu-g (group 2), and 8500-mu-g (group 3). AIM was performed on thyroid semithin sections. The mean I-129 concentration increased with the dose injected from group 1 (0.44 +/- 0.03-mu-g/mg, mean +/- SEM) to group 2 (2.05 +/- 0.14-mu-g/mg) and decreased in group 3 (0.57 +/- 0.08-mu-g/mg). When compared to control group (4.14 +/- 0.17-mu-g/mg), the mean I-127 concentration was not changed in group 1 (4.52 +/- 0.07-mu-g/mg), but altered in the other groups: It was significantly increased (7.14 +/- 0.41-mu-g/mg) in group 2 and slightly decreased (3.11 +/- 0.26-mu-g/mg) in group 3. These results underline the interest of AIM in the study of the effects of various doses of iodide on the thyroid autoregulation by iodide, a trace element actively trapped by this gland.