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Transplantable tumours were induced in the thyroids of Fischer 344 rats fed thiouracil (TU) in a moderately low iodine diet for 8–13 months. Pieces of hyperplastic thyroid were implanted subcutaneously into rats fed a TU containing diet. Almost all implants gave rise to very small vascularized transplants but there were three significantly larger, pieces of which were transplanted again and gave rise to the tumour lines. From the third transplantation generation on, pieces of tumours were implanted into rats treated to have elevated circulating thyrotropin and a group fed a high iodine diet. With some exceptions, the implants grew only in rats fed the TU or a low iodine diet and yielded TSH-dependent tumours. Almost all the tumours observed initially were papillary, and most of the remainder had colloid-filled follicles bounded by columnar cells. One line of tumours was of the latter type for eight generations. The others had more complex histories, in which there were sublines that were papillary for eight or nine generations, whereas, others became progressively more cellular or follicular, and more heterogenous with respect to histological types present per section at rates that varied with the subline. The large number of population doublings necessary to make a one gram tumour from a single original tumour cell indicates that the cells of dependent papillary tumours were immortalized.

Transplantable tumors of the thyroid gland have been produced by feeding of thiouracil (TU) to inbred Fischer 344 rats followed by the transplantation, initially, of pieces of hyperplastic thyroid gland, and in later generations, of pieces of transplanted tissue into similar rats or into rats fed a high iodine diet. In early generations, transplants grew only in the rats fed the TU diet, and this tissue was called dependent, whereas if the tissue grew in rats fed the high iodine diet in the abscence of TU, it was called independent. Dependent tumors were, initially, either papillary or of follicles distended with colloid. Later generations of some sublines were cellular or microfollicular in pattern and some became progressively more heterogeneous with later generations. Independent tumors began to appear by the third transplant generation. They were, initially, relatively uniform in pattern, and some tended to remain so, whereas other sublines exhibited some heterogeneity. Tumors had patterns that were cellular, or microfollicular, or follicular or had open follicles, etc.; there was one cellular ascites tumor subline. Other observations were made of vascular patterns, connective tissue, necrosis, and metastases.

A quantum system of N identical particles is described by the wave function $$\Psi = \Psi ({q_1}, \ldots {q_N}),$$ (8.1) where q j denotes all compatible coordinates of particle j (position and spin, for example). However, not all wave functions of this sort, which satisfy the time-independent Schrodinger equation, are acceptable representations of a quantum system. We also require a symmetry property, $$\Psi ({q_1}, \ldots ,{q_i}, \ldots ,{q_j}, \ldots ,{q_N}) = \pm ({q_1}, \ldots ,{q_j}, \ldots ,{q_i}, \ldots ,{q_N}),$$ (8.2) which indicates that the quantum state of the system does not alter if we change the coordinates of two particles. The symmetric wave functions are associated with integer spin particles (photons, phonons, magnons, 4He atoms). These particles are called bosons, and obey the Bose—Einstein statistics. The antisymmetric wave functions are associated with half-integer spin particles (electrons, protons, atoms of 3He). These particles are called fermions, and obey the Fermi—Dirac statistics.

A classical system of N monatomic particles of mass m may be given by the Hamiltonian $$H = \sum\limits_{i = 1}^N {\frac{1}{{2m}}} \vec p_i^2 + \sum\limits_{i < j} {V(\left| {{{\vec r}_i} - {{\vec r}_j}} \right|)} ,$$ (6.1) where \(V(\left| {\vec r} \right|)\) is a pair potential, as sketched in figure 6.1. The potential of a realistic system displays a hard core, \(V(r) \to \infty ,{\text{ for }}r = \left| {{{\vec r}_i} - {{\vec r}_j}} \right| \to 0\), and a suitably vanishing (for r → ∞) attractive part. The canonical partition function of this classical system, in contact with a heat reservoir at temperature T, in a container of volume V, is given by the integral in phase space, $${Z_c} = \int { \cdots \int\limits_V {{d^3}{{\vec r}_1} \ldots {d^3}{{\vec r}_N}\int { \cdots \int {{d^3}{{\vec p}_1} \cdots {d^3}{{\vec p}_N}{\kern 1pt} \exp {\kern 1pt} ( - \beta H),} } } } $$ (6.2) where the spatial coordinates are restricted to the region of volume V. The trivial integration over the momentum coordinates may be written as a product of 3N Gaussian integrals of the form $$\int\limits_{ - \infty }^{ + \infty } {dp{\kern 1pt} \exp ( - \frac{{\beta {p^2}}}{{2m}})} = {(\frac{{2\pi m}}{\beta })^{1/2}}.$$ (6.3)

The ultrastructure of the thyroid epithelial cell was examined at various time intervals after induction of involution of the hyperlastic thyroid gland. Thyroids were made hyperplastic by the feeding of thiouracil in a Remington low-iodine diet to male Fischer rats for 3 weeks. Involution was induced by replacing the thiouracil-containing diet with Purina Laboratory Chow, a high-iodine diet. During involution, organelles that play a role in the synthesis and secretion of thyroglobulin, such as the rough endoplasmic reticulum, Golgi apparatus, and apical vesicales, were well preserved and prominent features of the epithelial cell. The apical plasma membrane of many cells was highly irregular for approximately 2 weeks with signs suggesting rapid discharge of apical-vesical contents into the lumen of the follicle. Pseudopods and colloid droplets were present but were not very prominent features of the cell. No signs of extensive autophagy or obvious increased incidence of lysosomes were present, although there was an elevation in the incidence of small dense bodies starting about day 8, and prominent by 15 days. Some of these may be phagosomes formed from luminal debris. The observations indicate that in volution of the hyperplastic thyroid in which there is maintenance of the protein synthetic apparatus and little sign of autophagy or death of the epithelial cells is remarkably different from phenomena occurring during involution of prostate or mammary glands.

The ultrastructure of mitosis was studied in polarized, well-differentiated thyroid epithelial cells in vivo following stimulation with the goitrogen, thiouracil, and attention was focused on changes occurring in cytoplasmic organelles. RER cisternae appeared from mid-prometaphase to mid-telophase to undergo a vesicular transformation from lamellar profiles to smaller, rounder profiles with an up to 60% lower concentration of bound ribosomes. The Golgi apparatus underwent a nearly parallel breakdown/reformation process, and Golgi remnants were frequently associated with large clouds of smooth-surfaced 70-nm-diameter vesicles. Apical vesicles, believed to contain thyroglobulin, were found to accumulate during mitosis, reaching about six times their interphase concentration by mid-telophase, when they were observed in large clusters about the spindle poles. Clusters of apical vesicles then appeared to migrate to their usual apical location. Changes in the distribution of lysosomes were noted in late prometaphase, when they became aggregated into clusters, and in early telophase when they accumulated near the cleavage furrow.

To study blood capillary growth in the hyperplastic thyroid gland, rats were fed 0.25% thiouracil in a low iodine diet for time intervals up to 100 days. Thyroids were fixed by vascular perfusion and embeded in Epon. Whole lobes were sectioned from pole to pole and slides were prepared of sections every 0.3 mm. Capillaries were clearly enlarged by 3 days and they enlarged progressively thereafter. By 3 days, the cells of many neighboring capillaries came into close apposition and from this time on, there was evidence of fusion of capillary walls in the form of partial septa in the capillary lumens. Fusion continued until 20 days, when follicles were almost completely surrounded by a continuous endothelial sheet and unfused capillary walls were separated by connective tissue. The vascular pattern around peripheral follicles changed in a way similar to interior follicles, except that in places, capillaries were gradually excluded from the space between epithelium and thyroid capsule. Vascular enlargement was restricted to the thyroid blood vessels. There was no obvious enlargement of the blood capillaries of the parathyroid despite its close proximity to the thyroid.

We have tried to ascertain the site of iodination in the chronically stimulated, hyperplastic thyroid gland of rats. Rats were fed propylthiouracil in a commercial rat diet for 10 days. Then the diet was changed to a low iodine diet for 5 days. To label the gland, 10 mCi of 125I-iodide was injected into the left heart ventricle. Ten seconds later the animal was perfused through the left ventricle with a fixative solution containing a goitrogen to block further iodination, and stable iodide to help extract uncombined radioiodide. Electron microscopic autoradiographs prepared from the fixed thyroids show strong labeling over the lumen of the follicle and no consistent labeling of any other site or organelle. We conclude that the site of iodination in the chronically stimulated, hyperplastic thyroid is the follicular lumen, i.e. the same as that in the normal gland.

Inverted thyroid follicles in suspension culture were observed using dark-field illumination and time-lapse video enhancement techniques. The lumens of many follicles undergo episodes of rapid shrinkage followed by relatively slow dilation. The extent of shrinkage ranged from 10 to 40% of the initial diameter. The decrease in lumen diameter is accompanied by loss of luminal fluid. The rate of efflux of fluid amounted to from 1 to 90 μm 3 /μm 2 of luminal surface/min. This was followed after several minutes by a slow and generally linear increase in lumen diameter with time that could be accounted for by an influx of fluid of the order of 0.5 μm 3 /μm 2 /min. It is possible that this phenomenon is due to a continued influx of fluid into the lumen until a junction opens between cells allowing a sudden loss of luminal fluid. The junction reseals and fluid begins to accumulate in the lumen. The phenomenon may be a three-dimensional analogue of the behavior of domes.

A heretofore undescribed feature consisting of closely packed pits 0.5-1 micron in diameter was observed on the apical surface of thyroid epithelial cells. The walls of the pits were generally smooth, except at the base where there was a high incidence of irregularities looking like sites of recent fusion of apical vesicles with the pits. The matrix of the partition between pits was similar to the matrix of pseudopods in these cells in being free of membrane-bounded organelles and containing a low concentration of ribosomes. The pits were observed early in the involution of the hyperplastic gland, most prominently between 14 h and 8 days of involution. This is a time when thyroglobulin is accumulating in follicular lumens and the apical end of the epithelial cells usually contains a high concentration of apical vesicles ordinarily considered to be exocytic in character. It is important to recognize the existence of this feature to avoid confusing profiles of it with structures involved in macropinocytosis.

The ultrastructure of cytokinesis in rat thyroid endothelial cells in vivo was studied. The spindle axis of these cells was generally parallel to the surface of the vessel. A typical, microfilamentous contractile ring was associated with the cleavage furrow. The terminal phases of cytokinesis appeared to be accomplished by narrowing at the end(s) of the intercellular bridge (IB) where circumferentially oriented microfilaments were observed. No stretching of the IB was apparent. The furrow surface showed an increased concentration of microvilli and blebs, and an accumulation of 12-nm-diameter uncoated vesicles was frequently apparent in the nearby cytoplasm. Junctions between the mitotic and neighboring cells were maintained during cytokinesis, even in the region of the IB. Abluminal to the IB, new junctions between the daughter cells were observed. Accumulations of extravasated lipid particles and occasionally erythryocytes were found relatively frequently in the vicinity of IBs, suggesting that a complete luminal seal was not always maintained during cytokinesis.

The site of iodination of protein in the thyroid gland (whether intracellular or intraluminal) was ascertained by autoradiographic studies using iodide-125I. In tissue fixed within about 40 sec after intravenous injection of radioiodide the silver grains of autoradiographs were concentrated over the follicular lumen generally as a ring of grains close to the apical border of the follicular cells. The zone of grains was sharply limited toward the cells. No concentration of silver grains was detected associated with any intracellular organelle. The autoradiographic ring which had a minimum width of about 2 mum was continuous along the apical plasma membrane of the follicle cells but there was a drastic reduction in grain density along the plasma membrane of the distal portion of pseudopods. Tissue was fixed so soon after radioiodide injection that it appeared likely that a negligible fraction of radioiodoprotein, if formed in the cell, could have been transferred to the lumen. The observations strongly indicate that the iodination of thyroglobulin occurs in the follicle lumen, probably at the apical surface of the follicle cells. Since in the TSH-treated animals the distribution of the labeling along the apical plasma membrane agrees well with the reported histochemical distribution of thyroperoxidase in this membrane, it is further concluded that iodination may well be catalyzed by peroxidase in the apical plasma membrane.

We have been investigating the extent to which separated thyroid follicles in suspension culture, free of endothelium and fibroblasts, have the properties of follicles in vivo. To test whether thyrotropin (TSH) can cause thyroid epithelial cells to undergo mitosis, preparations of follicles suspended in Coon's modified F-12 medium with 0.5% calf serum were incubated with 10 milliunits of impure or pure TSH per ml. Three results were obtained: (i) TSH preparations stimulated the incorporation of [3H]thymidine into cell nuclei; (ii) mitotic figures were induced and they had the same characteristic ultrastructural features as those observed in vivo; and (iii) the cell number doubled in the course of 3 days of exposure to TSH. The results suggest that TSH is a mitogen for the principal thyroid epithelial celland that other substances found in the usual impure TSH preparations are not necessary for the mitogenic activity. It can act in the absence of nonfollicular cells. The initial multiplication rates are similar to those in vivo. The cells do not have to spread to divide in contrast to the requirement for spreading in the case of fibroblasts.

As an early step in the secretion of thyroid hormones, colloid droplets are formed by pseudopods of thyroid epithelial cells. However, such droplets are generally absent from thyroid stimulating hormone (TSH)-stimulated thyroid follicles in places where luminal colloid has been largely resorbed. To investigate the reason for this absence, stimulated thyroid follicles were examined. Even in markedly colloid-depleted lumens, pseudopods were frequently observed. These were often short and flat, abutting against the opposing epithelial surface and following its contour. No room appeared available for these pseudopods to roll up to form colloid droplets. In addition, ultrastructural changes were often visible in the opposing surface just subjacent to regions of pseudopod contact. These changes consisted of the loss of apical microvilli and the formation of an organelle-excluding microfilamentous meshwork, suggestive of early psuedopod formation. The possibility that contact with a pseudopod might be capable of inducing the formation of a second pseudopod was also suggested by the frequent finding of pairs of pseudopods, one abutting against or partially enveloping another.

Separated thyroid follicles in suspension culture invert in 5% serum. In some, the inversion is not complete in that a small normal follicle persists completely in the interior of an inverted follicle. In inverted follicles the lumens are distended and electron lucent. The bounding epithelial cells are stretched, have relatively few microvilli on the surface toward the medium but they have bundles of oriented microfilaments usually located near the lumen. The cells are connected together by tight junctions. When inverted follicles are punctured, the lumen shrinks, the cells retract and become cuboidal and microvilli reappear. Microfilaments persist at the luminal surface but no longer in oriented bundles. No appreciable extracellular matrix is present at the basal cell surface in contact with the lumen, but matrix is occasionally observed between cells. Since bundles of microfilaments like stress fibers are observed in the cells in suspension culture, the presence of stress fibers in cells in monolayer culture is probably not dependent on attachment but might be a reflection of the spreading of the attached cells.

The thyroid gland of the C3H mouse is composed largely of the usual follicle but it also contains a second kind of follicle. To ascertain the embryologic origin of the cell types in each of these follicles, ventral pharyngeal outpocketings and ultimobranchial outpocketings were isolated (before they fused to form the thyroid gland) from the 12-day-old fetus of the C3H mouse. The outpocketings were implanted into different kidney capsules of adult C3H mice and were allowed to grow for several months. Transplants were then excised and examined by electron microscopy. The ventral contribution formed large aggregates of follicles and was recognized as a distinct bump on the surface of the kidney. It formed only typical thyroid epithelium arranged in follicles containing colloid. On the other hand, the ultimobranchial contribution usually formed only a small number of follicles, generally of small size. It was readily located because the follicles occurred next to a white plaque of bone or cartilage at the site of implantation. The ulti-mobranchial contribution formed follicles containing four cell types: a ciliated cell, a cell with abundant agranular reticulum, a cell with many free ribosomes and fiber and occasional hemidesmosomes, and the C cell which was the most frequent cell type. No typical thyroid epithelium was observed in the ultimobran-chial transplant. These observations suggest that the C cell in the usual follicle is derived from the ultimobranchial contribution, and that the second kind of follicle is largely an ultimobranchial contribution but the typical thyroid epithelium in it is largely or entirely a ventral contribution.

Serial cross sections of typical thyroid epithelial cells of the Fischer rat revealed a closely but irregularly spaced circumferential layer of desmosomes just basal to the tight junction. A dense bundle of 60-A diameter microfilaments, running parallel to the lateral plasma membrane, was consistently found near this layer of desmosomes and appeared to be joined to them by microfilaments coming from the desmosomes. Rough ER and mitochondria appeared closely associated with the bundle of microfilaments.

In addition to pseudopods, somewhat pleomorphic blebs were consistently found protruding from the apical surfaces of hyperplastic rat thyroid epithelial cells into the follicular lumens in vivo. Many blebs were knobby, roughly hemispherical protrusions, with a diameter of 2-3 mum. Such blebs had a densely packed microfilamentous core and contained numerous apparent ribosomes. They were morphologically similar to blebs that have been observed in a variety of cultured cells. Other blebs were larger, more elongate, and less knobby, but had a similar ultrastructural organization. Blebs of all sizes appeared to be phagocytosed on some occasions by nearby epithelial cells. The phagocytic process involved partial engulfment of the bleb by a typical epithelial pseudopod, followed by an apparent pinching-off process, presumably resulting in the separation of the bleb from its cells or origin. The pinching-off process was associated with a band of approx. 6-nm diameter microfilaments that developed within the pseudopod cytoplasm surrounding the base of the bleb and is postulated to function as a contractile ring. The finding of blebbing is an intact tissue in vivo indicates that this phenomenon is not restricted to cultured cells, and thus tends to extend the significance of in vitro observations of the process. In relation to their occurrence in the hyperplastic thyroid gland in vivo, possible interconversions are considered between different types of blebs, and between blebs and pseudopods.

The morphology of the tight junction of rat thyroid epithelium was examined in freeze-fractured material fixed in glutaraldehyde and briefly glycerinated. In normal thyroids the overall appearance of this junctional specialization resembled that of other cell types in many respects. Short-term changes in thyroid activity and hypophysectomy for 3 wk did not obviously affect the appearance of tight junctions. Feeding of the goitrogen, thiouracil, which stimulates secretion of thyroid-stimulating hormone, resulted in the appearance of some very narrow and some very wide, tight junctions or sometimes junctions with both wide and narrow regions within the same cell.

The ultrastructure of mitosis in thyroid follicular epithelial cells of untreated 7-day-old rats was investigated. While most of the nuclear and cytoplasmic events in these animals were similar to those previously observed in goitrogen-stimulated adult animals, one new feature of mitosis in the young animals was the consistent finding of a characteristic, mitosis-associated apical protrusion (MAAP), extending into the follicular lumen. MAAPs were generally dome-shaped, with a 3- to 5-μm base. Their cytoplasmic content was essentially indistinguishable from that of the remainder of the cell. MAAPs had a high concentration of microvilli. These microvilli were frequently club-shaped with distal expansions which were more electron-lucent than normal microvilli. Club-shaped microvilli were also often observed on late prophase and prometaphase cells, preceding the actual development of protrusions, which were observed only from metaphase through telophase. A maximum of one MAAP was found per cell, but MAAPs were observed in 87% of those sections of mitotic cells from metaphase to telophase in which at least 2 μm of apical surface was visible.

Rats fed the goitrogen, thiouracil, were found to undergo a microhemorrhagic process within the thyroid gland, sometimes resulting in the deposition of red blood cells (RBCs) within follicular lumens. In such instances, erythrophagocytosis by follicular epithelial cells was frequently observed. This involved progressive RBC engulfment by an apical epithelial pseudopod, which conformed closely to the contour of the (often irregular) RBC and appeared to almost totally exclude luminal colloid from the completed phagosome. Completed phagosomes were retracted into the apical epithelial cytoplasm, and a periphagosomal accumulation of 7-nm microfilaments was often observed at this stage. Another feature of thyroid epithelial erythrophagocytosis was the occasional finding of apparent pseudopod-induced RBC fission. This was suggested by the observation of narrow, elongated RBC necks, surrounded by thickened pseudopods containing densely packed microfilments immediately adjacent to the RBC necks. It seems likely that these microfilaments play a role in the fission process, possibly functioning as a contractile ring.

We have prepared thyroid follicles in suspension culture to use as a model system in vitro for investigation of some properties of the thyroid gland. The follicles were free of endothelial cells, fibroblasts, and other nonepithelial cells. They were prepared by collagenase treatment of minced rat thyroid glands followed by differential filtration of the suspension through nylon meshes. Small clusters of principal thyroid epithelial cells were separated from large fragments and single cells. They were cultured in dilute suspension in Coon's modified F-12 medium in dishes coated with agarose to avoid having the cells attach to the dishes. By culture day 3, most of the clusters formed closed follicles containing a periodic acid-Schiff-positive colloid but without a basal lamina. Follicle walls contained an occasional C cell. The epithelium resembled that in the thyroid of a recently hypophysectomized rat, with normal polarity and organelle complement normal with respect to position and abundance, with basally located lysosomes, no pseudopods, and no colloid droplets. The cells were responsive to thyroid-stimulating hormone (thyrotropin) and to dibutyryl cyclic AMP. Thyroid-stimulating hormone at 10 munits/ml resulted in apical migration of lysosomes and formation of pseudopods and colloid droplets within 30 min; longer exposure resulted in depletion of luminal colloid. The results indicate that the suspended follicles resemble follicles in vivo with respect to morphology and responsiveness to thyroid-stimulating hormone in the absence of other cell types.

The ultrastructure of cytokinesis in vivo was studied in rat thyroid follicular epithelial cells. Where it could be ascertained, the spindle axis appeared tangential and the cleavage furrow perpendicular to the follicular luminal surface. The furrowing process was associated with a typical microfilamentous contractile ring and resulted in the formation of a short intercellular bridge (IB), usually located initially about midway between the base and apex of the daughter cells. The IB then appeared to undergo a migration process and was observed progressively closer to the apical surface. Just basal to the apically migrated IB, a new tight junction was observed between the daughter cells and—in presumed continuity with nearby retained tight junctions to neighboring cells—eventually formed a seal basal to the IB prior to its removal. Final separation of the daughter cells occurred without apparent stretching of the IB. The IB underwent degenerative changes and eventually appeared to be phagocytosed by one of the epithelial cells.

Ventral pharyngeal outpocketings and ultimobranchial outpocketings from the 14-day-old fetus of the Fischer rat were isolated before they fused to form thyroid glands. The outpocketings were implanted into different kidney capsules of adult male Fischer rats, and were allowed to grow for several months. Transplants were then excised and examined by electron microscopy. The ultimobranchial outpocketing gave rise to two types of follicles. One contained ciliated cells, cells with an abundant agranular reticulum, U cells with basal hemidesmosomes, and two types of cells with secretory vesicles. The other contained C cells separated from the follicular lumen by a single flat fiber-containing cell. The ventral outpocketing formed typical thyroid epithelium making up the usual thyroid follicles differing from follicles in the thyroid in situ by the absence of C cells. These follicles were functional as determined by autoradiographic studies with 125I but differed from thyroid follicles in situ with respect to size distribution. The results suggest that (1) in the adult thyroid gland the C cell in the usual follicle is an ultimobranchial contribution and (2) the so-called ultimobranchial follicle is ultimobranchial in origin but that the typical thyroid epithelium in mixed follicles of U cells and typical thyroid epithelium is a ventral contribution. The reason for the absence in the thyroid gland in situ of the variety of other cell types observed in ultimobranchial transplants is unknown.

In addition to the usual functional follicles, thyroid glands of normal C 3H mice contain a second kind of follicle distinguished by heterogeneous, “foamy” colloid, by ciliated epithelial cells, and by previously unreported epithelial cells, termed AR cells, with distinctive abundant agranular reticulum. Flecks of immiscible substance of low density impart the foamy appearance to the colloid and often adhere to the surfaces of the epithelial cells. The ciliated cells possess a uniform array of apical cilia and a scattering of long, branched microvilli; their cytoplasm contains numerous mitochondria but is otherwise sparsely populated with agranular reticulum, nondilated granular reticulum, and free ribosomes. The AR cells, in addition to their prominent agranular reticulum, contain numerous large mitochondria and occasionally glycogen, presumed secretory globules, and nondilated granular reticulum. Approximately half of the epithelial cells in this second class of follicles are indistinguishable from typi...

The concentration and specific activity of radioiodine in the rat thyroid were measured at various times during the equilibration of thyroid iodine with dietary iodine labeled with 125I. Both rose rapidly and linearly over the first few days; then the rate of increase began to decrease progressively. At 99 days, the last time at which measurements were made, the specific activity in the thyroid had closely approached that in the diet, but the concentration of radioiodine in the thyroid still appeared to be increasing slowly. The equilibration process for the thyroid gland as a whole deviated significantly from first order kinetics. The major reason for this deviation seems to have been the heterogeneity of equilibration rates in various iodine pools; the effects of other biological and experimental factors appeared to be small. (Endocrinology 81:1063, 1967)

The dependence of the ratio of the radioiodide concentrations in thyroid gland and serum ( T/S) on the serum iodide concentration for fixed serum thiocyanate concentrations was investigated in C3H mice. The empirical equation (See PDF for Equation) where [SCN–] and [I–] are the serum thiocyanate and iodide concentrations in mg %, fitted the data within the limits of experimental error. Interpretation of the empirical equation was based on simple adsorption and active transport models of the iodide concentrating mechanism. The inhibition by thiocyanate of the thyroidal iodide concentrating mechanism appears to be competitive.

Mature ultimobranchial follicles in the Fischer rat thyroid are characterized by being lined by two or more layers of cells (U cells) and by having an abundance of desquamated cells in the lumen. Such follicles, of variable size and shape, were found in almost every lobe in rats at least 30 days old. They were usually in the interior of the lobe in contact with perivascular connective tissue. Ultimobranchial follicles with multiple layers of cells were not observed in the two‐day‐old rat indicating that these follicles are an example of postnatal development. The most common precursor in the rat was a follicle, relatively large compared with the usual thyroid follicle, containing some cells or debris. Other precursor structures included narrow tubes, sheets or spheroids of cells characteristically having little cytoplasm. Intermedlate forms between these precursors and mature ultimobranchial follicles were recognized. Cells were desquamated while nucleated, and, later, the nuclei disappeared. Thus, in some follicles non‐nucleated debris accumulated. Many follicles were composed of mixed populations of cells, both typical thyroid epithelium and U cells. The relative abundance of the two cell types varied markedly as did the proportions of colloid and cell debris. Copyright © 1971 Wiley‐Liss, Inc.

An investigation was made to determine whether the inhibition by thiocyanate of the thyroidal accumulation of radioiodine can be accounted for by the well-known inhibition of the iodide concentrating mechanism, or whether, in addition, there is a direct effect on the iodination process. At the lower concentrations of serum thiocyanate the decrease in the thyroidal accumulation of radioiodine was proportional to the ratio of the thyroid and serum radioiodide concentrations (T/S) and no appreciable effect on the rate of incorporation of radioiodide per unit of thyroidal radioiodide into protein-bound I131 (PBI131) was observed. At higher serum thiocyanate concentrations the fraction of the thyroid radioiodide incorporated into PBI131 per minute decreased as the uptake decreased whereas the T/S was relatively constant. However, at this higher range of concentrations no unambiguous interpretation of the effect of thiocyanate could be made because of the lack of information about the distribution of radioiodide in the internal compartments of the thyroid. A comparison was made also of the effect of thiocyanate on the T/S when the iodination process was permitted with the effect on the T/S when iodination was blocked.

ASTUDY of the dependence of the ratio of the thyroid radioiodide concentration to the serum radioiodide concentration (T/S ratio) on the serum iodide concentration has been reported in the rat by Halmi (1954). This paper reports a similar study in normal and hypophysectomized mice. In addition, using simple models, formulae have been derived describing the dependence of the T/S ratio on the serum iodide concentration and predictions of the formulae are compared with the appropriate experimental results in both mice and rats. MATERIALS AND METHODS Male C3H mice were used. The normal mice were four months of age at the time of the radioiodine study. The hypophysectomized mice were fourteen weeks old at the time of the operation which was done eight days before the radioiodine study. They were hypophysectomized through the parapharyngeal approach. Completeness of the operation was ascertained by visual inspection of the region of the sella turcica for pituitaiy fragments using a binocular microscope at 9 × m...

Estimates of the relative concentration of radioiodine in individual follicles at various stages of isotopic equilibration were made by microdensitometry of auto radiographs. Data at 1 hr after a single injection of radioiodide were used to obtain clearances of blood radioiodide by single follicles. For central follicles clearances appeared proportional to the surface area of the lumen. The observed size independence of the concentration at isotopic equilibrium indicated that clearance of luminal iodoprotein was proportional to the surface area of the lumen also. These results indicated that average uptake and release of radioiodine per cell are independent of follicle size. The analysis of the size distribution of radioiodine concentration in follicles at 4 days indicated that the fraction of iodine released per day varied inversely with the lumen diameter. Clearance of colloid was approximately 115 Mμ3 per cell per day. Results were similar for peripheral follicles except that clearances and exit rate c...

Autoradiographs of thyroidal organic radioiodine were made 1 hr after an injection of radioiodide and also at various times during the equilibration of rat thyroidal iodine with mI-labeled dietary iodine. Most follicular lumens were homogeneously labeled, but in some lumens organic radioiodine was restricted to the peripheral region of the colloid, producing an autoradiographic image in the shape of a ring. The incidence of follicles with a ring autoradiograph was high 1 hr after an injection of radioiodide but fell to a low level after 1 day of equilibrium labeling; however, an occasional animal killed up to 16 days after the start of equilibrium labeling had a relatively high incidence of ring autoradiographs. Some lumens had a ring autoradiograph even after 99 days of equilibrium labeling; this implies marked limitation of diffusion of radioiodoprotein in the colloid. In some lumens there was a homogeneous distribution of organic radioiodine in relatively low concentration throughout except for a narro...

The mature ultimobranchial follicle of the rat consists of two or more layers of cells (U cells) surrounding a lumen containing cell debris. The ultrastructure of the outer, or basal, U cell is characterized by the presence of half desmosomes on the basal plasma membrane and pinocytotic vesicles near it, by little granular reticulum but an abundance of free ribosomes, by clusters of fibrils connected to desmosomes and possibly free in the cytoplasm. The cell ages by accumulation of clusters of fibrils and it undergoes differentiation to form more apical U cells which contain fewer ribosomes and have fibrils dispersed in the cytoplasm. The apical U cell is desquamated into the lumen and ultimately becomes a carcass containing a dense matting of fibers and vacuoles containing a reticulated material resembling that in the lumen. U cells are observed associated with typical thyroid epithelium in the thyroid of the newborn rat in relatively large follicles containing colloid and desquamated cells. They also form rods of cells in the very young rat. Mixed follicles containing both U cells and typical thyroid epithelium occur at all ages.

A method for the autoradiographic localization of water-soluble diffusible ions has been developed and applied to the localization of iodide125 in the mouse thyroid gland. Frozen-dried thyroids of hypophysectomized mice containing radioiodine125 as inorganic iodide125 were embedded in paraffin. Sections were spread on mercury and mounted on autoradiographic film. After exposure the mounted section was permanently fastened directly over its latent image and tissue constituents were fixed by dipping in 80% aqueous methanol. The preparation was air dried and then deparaffinized with petroleum either. After development and fixation, slides were stained with Nuclear Fast Red. In certain cases radioiodide could be localized primarily in the follicular epithelium. Control studies demonstrated that the autoradiographic image was not an artifact resulting from chemical induction or suppression of selected areas of latent image. A comparison of autoradiographs prepared from frozen sections and those prepared by freeze-drying showed similar localization of the radioisotope and indicated that there was no displacement of the radioiodide during paraffin embedding.

Thin sections of colloid cells in the thyroid gland of the C3H mouse were observed with an electron microscope. There appeared to be 2 main kinds of colloid cells. In the first, the clear appearance of the cytoplasm is due to the presence of a very dilated cisterna of the granular reticulum in an otherwise normal appearing cell. In the second, the plasma membrane of the cell appeared disrupted and there was extensive replacement of the cytoplasm by material resembling colloid. No information is available yet on the origin of colloid cells but it is quite clear that they are not specific for thyroiditis or other recognized diseases of the thyroid gland

The typical thyroid epithelium of the cream variant of the Syrian hamster differs from that of other common mammalian species. One obvious difference noted by light microscopy is that the cells contain numerous PAS‐positive granules apical to the nucleus. By electron microscopy these granules are dense granules resembling lysosomes. The cells have exceptionally long microvill and numerous junctions and interdigitations of lateral plasma membranes with those of their neighbors. Many organelles in the cells are stratified rather than arranged at random. In addition to the dense granules and centrioles, the Golgi apparatus is usually located at the level of the apical end of the nucleus. The granular reticulum is primarily in the basal half of the cell, although some is apical. Microtubules are especially abundant and are located ainly close to the lateral surfaces and around the nucleus, although some are near apical or basal plasma membranes. The microtubules frequently appear to be in contact with mitochondria and dense granules, but their role in the positioning or stratification of organelles is uncertain. Copyright © 1971 Wiley‐Liss, Inc.

The radioiodide and the protein-bound radioiodine (PBI131) concentrations in the thyroid gland and the serum radioiodide concentrations in mice and rats were measured at various time intervals (up to 25 hr) after injection of radioiodide. The ratio of the radioiodide concentrations in the thyroid gland and serum (T/S) increased progressively with the time interval after injection. If it is assumed that a small but constant fraction of the thyroid PBI131 decomposed during the fractionation of the thyroid I131, the corrected thyroid radiodiode concentration yielded a constant T/S up to 4 hr after injection and the rate of increase of the thyroid PBI131 was proportional to the thyroid radioiodide concentration. The corrected data were therefore consistent with a previously published simple model. Analysis of the source of thyroid radioiodide indicated that at 4 hr after injection almost all was derived from blood serum, but at 25 hr most could have been derived from thyroidal PBI131 by physiological degradation.

IN SOME recent studies the ratio of the thyroid radioiodide concentration to the serum radioiodide concentration (T/S ratio) was higher when binding of radioiodide was blocked by a single injection of either propylthiouracil (Wollman and Scow, 1953) or iodide (Wollman and Scow, 1954b) than when binding was permitted. These observations are in agreement with conclusions reached in a theoretical analysis (Wollman, 1954) that merely blocking binding of radioiodide would be expected to elevate the T/S ratio provided that the iodide binding rate was fast compared with the rate of equilibration of iodide between thyroid gland and blood. It was also recognized (Wollman, 1954) that a goitrogen might elevate the T/S ratio by some mechanisms in addition to that of blocking binding. Several studies have been made to ascertain whether such mechanisms exist. The results of one study indicated that propylthiouracil administration increased the T/S ratio by a mechanism in addition to the expected effect of blocking bind...

The organic binding of radioiodine by the thyroid gland of the mouse was blocked within 1 minute by the intravenous injection of 1 mg of propylthiouracil (PTU). In mice fed a very low iodine diet the ratio of the radioiodide concentration in the thyroid gland to that in the serum (T/S) was reduced significantly by injection of 1.5 µg of iodide 15 minutes before intravenous PTU injection. The amount of iodine bound prior to PTU injection was only a small percentage of the total iodine in the thyroid gland. This reduction did not occur in mice with less active thyroid glands. However, in the latter mice, doses of 22.5 µg of iodide or more injected 90 minutes before PTU caused a small but systematic decrease in the T/S when compared at fixed serum iodide concentration with mice given PTU before the iodide. In addition, in these mice given both PTU and iodide the T/S was greater than in mice given iodide but no PTU. It is concluded that the organic binding of iodine causes a decrease in the T/S in mice with active thyroid glands. In addition, PTU increases the T/S in mice in which organic binding of iodine is blocked by iodide.

Shortly after the administration of 1/40 unit thyrotropin to rats, 24 hours post-hypophysectomy, the following sequence of changes has been observed within thyroid follicular epithelial cells: (1) the appearance of apical cell surface activity consisting of pseudopods projecting into the follicular lumen; (2) apparent phagocytic engulfment of colloid droplets lacking indications of acid phosphatase activity; (3) close association and probable fusion of newly formed colloid droplets and dense granules, the latter cytochemically positive for acid phosphatase activity; (4) the appearance of presumptive acid phosphatase activity within colloid droplets; and, (5) further colloid droplet changes, viz., basipetal migration and decrease in size, accompanied by an increase in density and in demonstrable acid phosphatase activity. These changes appeared to represent the resorption and degradation of follicular colloid. Comparable results were obtained using intact and more heavily stimulated animals. Colloid biosynthesis was tentatively visualized in these cells as a separate mechanism involving small vesicles prominent in the Golgi region and beneath the apical plasma membrane of some, but not all, thyroid follicular cells in each specimen.

A new cell with relatively little cytoplasm has been identified in the second kind of follicle in the C3H mouse thyroid gland. It has as ultrastructural characteristics the presence of clusters of fiber in the cytoplasm, vesicles near the basal plasma membrane, and half desmosomes in the basal plasma membrane. It resembles the U cell found in the ultimobranchial follicle of the Fischer rat thyroid, but has a somewhat larger amount of granular reticulum. It is found in the follicle wall between other epithelial cells and the basement membrane, but occasionally is in contact with the lumen. It also occurs as a double layer in the follicle wall. Cell debris in the lumen of the follicle contains fibrils and may be the result of desquamation of this fibril‐containing cell. Copyright © 1972 Wiley‐Liss, Inc.

IN MODELS describing the kinetics of accumulation of radioiodine by thyroid tissue it has been assumed that the equilibration of radioiodide between blood and thyroid tissue is instantaneous (Myant, Pochin and-Goldie, 1949; Oddie, 1949; Brownell, 1951; Riggs, 1952; Wollman, 1953). However, recent measurements show that the equilibration is not instantaneous in the mouse (Wollman and Scow, 1953). In addition, the following simple calculation shows that the equilibration must be expected to take an appreciable length of time if the ratio of the radioiodide concentrations in thyroid gland and serum (T/S ratio) is large. The T/S ratio has been found to be approximately 250 in the normal mouse (Wollman and Scow, 1953). This implies that at equilibrium the radioiodide content of the thyroid is 250 times that of an equal volume of serum or (approximately) blood.2 If one assumes that the radioiodide concentration in the blood of the mouse is held constant after injection

After administration of C14-labeled thiocyanate, the concentration of C14 in the thyroid gland following equilibration was about half that in the serum of normal and hypophysectomized C3H mice. Paper chromatography of the serum revealed that 90% of the C14 was in the form of thiocyanate. These results, coupled with a previous analysis which indicated that thiocyanate competitively inhibited the thyroid iodide concentrating mechanism, appear to eliminate the possibility that concentrated iodide is held in the thyroid by adsorption.

At short time intervals after injection of iodide-125 to mice, the concentration of inorganic iodide-125 in the thyroid epithelial cells of some follicles was much higher than in the lumen of the follicle or in blood vessels as demonstrated by autoradiographic methods. This finding in both binding and propylthiouracil-blocked thyroid glands suggests that the basal cell membrane is responsible for iodide concentration. The persistence of an autoradiographic image over the follicular cells for at least 5 min after iodide-125 injection suggests that the apical cell membrane exerts some control over the passage of radioiodide from the cell into the follicular lumen. (auth)

RECENT studies by Wollman and Scow (1953) on mice indicated that when binding of iodine was blocked by a single injection of propylthiouracil the ratio of the radioiodide concentrations in the thyroid gland and serum (T/S ratio) was greater than when binding was permitted. This paper reports similar data for normal and hypophysectomized rats. methods Experiments were performed on male Holtzman rats, 3 months of age. The rats were fed a lactating diet2 (Scow, 1953) since weaning. The iodine content of this diet was not measured. It was not low enough to cause thyroid enlargement (Table 1), but was low enough to yield rats with active thyroids as evidenced by high radioiodine uptakes and high T/S ratios. Rats were 30 days of age when they were hypophysectomized through the parapharyngeal approach. Completeness of hypophysectomy was ascertained by visual inspection of the region of the sella turcica for pituitary fragments using a binocular microscope at 9 × magnification.

In the young adult male Fischer rat there are mixed brown and white adipose tissue pads on the surface of the thyroid gland at the upper and lower poles of the lobes. When the thyroid gland was stimulated by feeding the rats 0.25% thiouracil in a low iodine diet, these adipose tissue pads became much less prominent. Examination of histological sections revealed that there were marked morphological changes in these pads. After feeding the animals the thiouracil-containing diet, thyroids and the adipose pads were fixed by perfusion with a solution of 2% formaldehyde, 2.5% glutaraldehyde, and 3% dextran in cacodylate buffer and postfixed in 1% osmium tetroxide in buffer, and whole lobes were embedded in Epon. The lobes were sectioned serially starting at one pole, and sections were usually examined every 0.3 mm. Adipose tissue was found only within 1.5 mm from each pole. Although thyroid tissue showed changes within 1 or 2 days, no obvious morphological changes were seen in the adipose tissue pads until appr...

When inverted thyroid follicles in suspension culture are embedded in a collagen gel, there is extensive reorganization of the follicle. To identify intermediate stages in the reorganization, a suspension of inverted follicles was mixed with a cold solution of collagen (0.1 mg/ml) in culture medium and the resultant was warmed and allowed to gel. Prior to embedding, the epithelial cells bounding the lumens formed a monolayer of attenuated cells with their microvilli-bearing surface in contact with the medium. The first change noted was a shrinkage of the lumen in many follicles by 18 h. The cells became cuboidal to columnar. Some of the cells had long sheet-like processes extending into the lumen in contact with those of other cells. In late stages of the reorganization, 48 h, the cells were arranged in a compact spheroid. The spheroids contained two different kinds of colloid-filled lumens, possibly of different origins, one a spherical microlumen, the other very long and narrow in section. The peripheral cells of the spheroid had a smooth plasma membrane (without microvilli) in contact with collagen. Although most of the cells in a section had a microvilli-bearing surface forming part of the boundary of a lumen, it is not certain that all cells were in contact with a lumen.