Acute effects of various doses of iodide on thyroid iodine autoregulation. A study with 129I by means of analytical ion microscopy.

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