Involution of thyroid hyperplasia
(1986)
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- The first part of our thesis is a review of the literature. The first chapter deals with the structure and physiology of the thyroid gland; in the second chapter the regulation of thyroid gland is reviewed. <BR> The second aprt includes our personal work. In the first chapter we describe various morphological, stereological and biochemical methods used in our study of the thyroid hyperplasia and involution. <BR> In the second chapter, the changes induced during thyroid hyperplasia with LID alone for 2 months and its involution with different doses of iodine, and with or without T4 are described. Involution with large doses of iodide is characterized in vascular network, neofolliculogenesis, increase in cell number and inflammation. Large doses of iodide which are not harmful for control animals, become thus toxic for iodine excess inhibits iodination, coupling and later on secretion of thyroid hormones through a Wolff-Chaikoff effect. <BR> During involution with MID these alterations are reduced and the gland resumes its normal structure. T4 alone is not sufficient to restore abnormal thyroid morphology as shown by persistent abnormal thyroid weight and follicular number. T4 with MID seems to be the best way to obtain a rapid and complete involution of thyroid hyperplasia but plasma T3 and T4 levels are elevated. Furthermore prolonged T4 administration induces a resting glandular state. <BR> Therefore, our results suggest that T4 association with iodide could be of interest in the treatment of diffuse non-toxic human goiter. <BR> In the third chapter, the role of iodide during involution is further analysed with respect to inter- and intrafollicular heterogeneity in young and old animals. Two different treatments, cycles of hyperplasia and involution or continuous involution after hyperplasia were tested. <BR> In young animal, cold or partly cold follicles were observed specially after involution, while a large colloid goiter was obtained after cycles. Partly cold follicles were even more numerous when the hyperplasia period was longer. Smaller proportions of partly cold follicles after cycles indicate that the alteration of the follicular iodine metabolism could be reversible. <BR> Cold and partly cold follicles develop spontaneously in aged animals. After hyperplasia followed by involution with large iodide doses, their proportion are reduced, suggesting again the reversible character of the functional alteration. We therefore disagree with the hypothesis of a genetic cause in the formation of cold follicles as proposed by others. As for the genesis of colloid goiter, we propose a disequilibrium between exocytosis and endocytosis as pathogenic mechanism. <BR> In the fourth chapter, the interstitial connective changes were analyzed in the gland during hyperplasia and involution. The interstitial connective tissue was increased during continuous hyperplasia as shown histologically and by measuring the glandular collagen content and concentration. This increment is probably a consequence of type I collagen synthesis by proliferating interstitial cells but certainly results from type IV collagen synthesis by follicles and capillaries which form new basement lamina as they grow. <BR> in all types of involution with HID, after short and long period of hyperplasia, necrosis associated with inflammatory and interstitial cells infiltration occurs and collagen accumulates. This accumulation is transient after short periods of hyperplasia while it lasts longer after long period of hyperplasia. This indicates that the length of continuous stimulation is critical for the extent of fibrosis during involution. The collagen produced during involution seems mainly of type I and of type III, which is known to be produced in inflammatory reactions. <BR> In general conclusion, although we were not able to get a animal model of goiter totally comparable to human nodular goiter, our results allow us to emphasize the key role of the dose of iodide and the length of hyperplasia during involution and transformation of the goiter into colloid and partly nodular. Experimentally we obtained, for the first time, follicular heterogeneity and thyroid fibrosis
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Hamudi, S. R. (1986). Involution of thyroid hyperplasia. https://hdl.handle.net/2078.5/112012