Ultrastructural changes in the rat thyroid gland during iodine deficiency

Thyroid ultrastructure changes were studied during the course of a low iodine diet in rats. At day 20, follicles were normal, but a number of them contained cells of higher density and with greatly elongated microvilli. Endoplasmic reticulum cisternae were frequently dilated. From day 20 until day 80, the most characteristic changes in the thyroid cells were the progressive accumulation of subapical peroxidase-positive exocytotic vesicles. After 80 days of the low iodine treatment, Golgi apparatuses were very active. Cell division could be observed. At this stage, exocytotic vesicles were generally very abundant. These data suggest that the remarkable accumulation of subapical exocytotic vesicles between day 20 and day 120 might represent an adaptation to the moderate and gradual increase in TSH stimulation that occurs in the conditions of low iodine diet.     

Localization of thyroid peroxidase and the site of iodination in rat thyroid gland.

The iodinated protein was localized in thyroid tissue slices by using radioautography. In unfixed tissue, the labelled protein was localized in the colloid, whereas, in tissue that was fixed before the 125I addition, the label was within the follicular cell. This localizes thyroid peroxidase largely on the endoplasmic reticulum of the cell.     

Interaction of bromine with iodine in the rat thyroid gland at enhanced bromide intake

In experiments with rats, we have found that at enhanced intake of bromide, bromine does not replace chlorine in the thyroid; it replaces iodine. Under our experimental conditions, more than onethird of the iodine content in the thyroid was replaced by bromine. In the thyroid, bromine probably remained in the form of bromide and, in proportional to its increased concentration, the production of iodinated thyronines decreased, with the sum of the iodine and bromine concentrations being constant at the value of 20.51±1.16 μmol/g dry wt of the thyroid. In contrast to other organs, the biological behavior of bromine in the thyroid is not similar to the biological behavior of chlorine but resembles more that of iodine.     

Radioautographic studies on the formation and maturation of bone marrow lymphocytes in mice

Abstract. DNA labelling by [³H]thymidine and the sandwich radioimmunolabelling method were used to characterize marrow lymphoid cells and to study the kinetics of production and maturation of small lymphocytes in the bone marrow of adult mice. Marrow lymphoid cells consisted of non-proliferating small lymphocytes, 30–40% of which had detectable surface immunoglobulin (SmIg), and proliferating large lymphoid cells lacking SmIg. Double-labelling experiments employing [³H]thymidine in vivo followed by sandwich radioimmunolabelling in vitro indicated that marrow small lymophocytes lack detectable SmIg when they are formed but develop SmIg within the first few days after production. Marrow lymphocytopoiesis includes; (1) praliferation of large lymphoid cells, which are presumptive small lymphocyte progenitors, which have a cell cycle time of 14–15 hr, and (2) a 3–5-day intramyeloid stage when many newly formed small lymphocytes undergo maturational changes towards the B cell lineage.     

Effect of long-term injection of high doses of potassium iodide on iodine metabolism in rat thyroid gland

Concentration of thyroid hormones in the serum of the rats after 14-day injections of potassium iodide (1, 3, 10, 100, and 500 physiological daily doses) did not differ from the control values. Excessive administration of potassium iodide increased the total iodide content in the rat thyroid tissue by 60–121% (35–108% and 94–128% for the protein-bound and free iodide, respectively), indicating the activation of the uptake and organification of iodide. The long-term injection of both low and high doses of potassium iodide increased the activity of catalase by 8–18% and SOD by 33–50% and enhanced the level of toxic LPO products reacting with thiobarbituric acid by 15–38%. It is suggested that reactive oxygen species and the excessive iodination of proteins (particularly thyroglobulin) induced by the long-term administration of high doses of potassium iodide can play an important role in the development of thyroid dysfunctions and autoimmune diseases.     

Measurement of thyroid hormone in the rat thyroid gland by radioimmunoassay

The present paper describes (i) a hydrolysis technique with Pronase and leucine aminopeptidase using one rat thyroid gland, resulting in maximum release of thyroid hormones and minimum deiodination, and (ii) a simple and rapid procedure for thyroid hormone radioimmunoassays in thyroid hydrolysates using commercial kits intended for serum thyroid hormone determinations. The procedure is used to determine T4, T3, and rT3 concentrations and hormonal molar ratios in a thyroid gland from a male Wistar rat. The reliability of the method is also studied.