Vascularization and iodide transport down regulation in rat goitre
Rognoni, J.B.; Penel, C.; Ducret, F.
Acta Endocrinologica 105(1): 40-48
1984
ISSN/ISBN: 0001-5598 PMID: 6695543 Document Number: 224246
The regulation of the amount of thyroid iodide and of its organification during the involution of an experimentally-induced goiter was investigated in the rat. The goiter was obtained by drastic I deficiency; male Wistar rats received an I-deficient diet for 6 mo., supplemented with PTU during the last 2 mo. The study was followed for 16 days after the beginning of I refeeding (daily I intake = 50 .mu.g). The thyroid iodide, total thyroid organic I and plasma iodide, PBI [protein-bound I] and TSH concentrations were determined from day 0 to 16 and compared to their control values (rats on a normal iodide diet for 6 mo.). In addition, a stereological study was carried out to determine if the extent of the gland vasculature might be implicated in the regulation of the thyroid iodide content. The plasma TSH concentration was very high and constant for 8 days (2.40 .+-. 0.37 and 2.45 .+-. 0.43 on day 0 and 8, respectively, vs. 0.25 .+-. 0.12 .mu.g/ml in control rats), while iodination and secretion were blocked for 4 days (0.34 .+-. 0.19 and 0.5 .+-. 0.1 on day 0 and 4, respectively, vs. 14.4 .+-. 2.0 .mu.g 127I/gland in control rats) (Wolff-Chaikoff effect). Thyroid iodide amount increased enormously for 2 days (2.5 .+-. 0.6 and 2.45 .+-. 0.55, respectively, on day 1 and 2 vs. 0.09 .+-. 0.01 .mu.g 127I/gland on day 0), then strongly decreased between 2 and 4 days (1.15 .+-. 0.27 127I/gland). The thyroid/serum (T/S) ratio iodide pump), which was very important between 0 and 2 days (115), decreased strikingly on day 4 (55). Moreover, the thyroid homogenates were shown to contain a new (non-proteic) iodocompound which escaped classical iodination. Its mobility during polyacrylamide gel electrophoresis was intermediary between those of iodoaminoacids and iodide. Its turnover rate was practically similar to that of thyroid iodide. This compound (termed X) accumulated until day 2 (0.39 .+-. 0.03 .mu.g 127I/gland), then decreased sharply as did thyroid iodide; neoiodination resumed (Wolff-Chaikoff escape). The stereological results showed that as soon as the iodide refeeding started, the volume density as well as the surface density of vessels sharply decreased (0.23 .+-. 0.03 .mu.m3/.mu.m3 and 0.06 .+-. 0.03 .mu.m2/.mu.m3 on day 0 and 8, respectively), while the same parameters for thyroid epithelial cells remained constant (0.35 .+-. 0.02 .mu.m3/.mu.m3 and 0.32 .+-. 0.03 .mu.m2/.mu.m3 on day 0 and 8, respectively. A great iodide influx in hyperstimulated thyroid epithelial cells induces a cellular control, antagonist to the TSH action on the amount of thyroid iodide. This control acts sequentially: an early regression of the thyroid vasculature is observed, which is followed by a regulation of iodide active transport. The X iodocompound might be one of the factors implicated in this control.