Colloidal aggregates of insoluble inclusions in human goiters

To shed some light on the physicochemical properties of the thyroid follicu lar colloid, we have screened retrospectively the autoradiographs of 60 hum an nodular goiters labeled 17 h preoperatively with 100 mu Ci I-125 for evi dence of colloid compartmentalization. In 87% (52/60) of all goiters examin ed, sporadic or multiple colloidal inclusions ('colloid stones') not mixing with newly labeled Tg were detected. The detailed analysis of 17 goiters r evealed a mean incidence of 0.09 +/- 0.11 'colloid stones' of variable size per follicle ranging from 0.02 +/- 0.01 (10) to 0.43 +/- 0.09 (5) (mean va lues +/- S.D., number of sections examined in brackets). In this study we d id not find a clear-cut association of incidence of 'colloid stones' with s ex, age or nosologic group (hyperthyroid, preclinically hyperthyroid, euthy roid). The existence of different colloidal compartments as demonstrated in this and other studies is of considerable importance for thyroid function, interpretation of iodine kinetics, and studies on the role of iodine on gr owth and function of the thyrocytes. Different thyroidal iodine compartment s could well be of functional relevance, for example in the adaptation of t hyroid hormone secretion to antithyroid drugs or in severe and prolonged io dine deficiency, when very slow compartments become an important source of minimal quantities of iodine and thyroid hormone. 'Colloid stones', for exa mple, may well explain the repeatedly observed, surprisingly large total io dine store in human endemic goiters, even in the presence of severe iodine deficiency. It is evident that the existence of multiple iodine compartment s and, in particular, of particulate slow-turnover pools complicates the in terpretation of total glandular iodine measurements with modem techniques s uch as X-ray fluorescence and positron emission tomography. (C) Societe fra ncaise de biochimie et biologie moleculaire / Elsevier, Paris.