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The effect of graded concentrations of propylthiouracil on the synthesis of labeled iodoamino acids was studied under in vitro conditions in which rat thyroid lobes are capable of synthesizing significant quantities of radioactive iodothyronines. The ease with which synthesis of the iodoamino acids was inhibited by PTU was in the following order: T3 and T4>DIT>MIT. Since the facility with which formation of each labeled substance was depressed by PTU was inversely related to its magnitude of formation in the absence of PTU, no definite conclusions as to relative susceptibility of the various biosynthetic steps to inhibition by PTU are possible. Nevertheless, the pattern of inhibition is similar to previous in vivo data. PTU enters the thyroid lobes from the medium rapidly enough to prevent organic binding of inorganic iodide present in the lobes before incubation. Apparently, iodide present in the inorganic form in the thyroid for long periods can be organically bound as rapidly as that newly entering the...

THYROID parafollicular cells contain calcitonin in a granular form. Reduction in numbers of granules and vesicles occurs during induced calcitonin secretion in vivo1, and from thyroid slices2. Particulate fractions with the biological activity of calcitonin have been derived from homogenates of pig, calf and rat thyroid glands3,4. We have prepared calcitonin containing particulate fractions from pig thyroid and have studied the properties of the isolated granules.

THE suggestion, based on clinical observation, that parahydroxypropiophenone1 is an effective inhibitor of thyrotropic hormone (1, 2) has not to date received any experimental support (3, 4). The chief evidence against such an action is the fact that the goitrogenic effect of propylthiouracil, known to be mediated through the anterior pituitary, is not cancelled by this agent. Our own studies herein presented are in agreement on this point but differ from those cited, in that the administration of parahydroxypropiophenone alone was associated with distinct changes in the thyroid, the adrenal, and the pituitary. EXPERIMENTAL PROCEDURE Growing female rats of the Wistar strain, approximately 42 days old, were maintained on ground pellets with and without the addition of parahydroxypropiophenone or propylthiouracil, alone or in combination, as noted in Table 1. At the termination of each experiment serum was obtained for protein-bound iodine analyses (5, 6) and weights of the thyroid, adrenal, and pituitary g...

A small amount (3–4 per cent) of the homogenate of normal rat thyroid glands, labelled with radioiodine, resists enzymatic digestion by pancreatin and pronase and remains at the origin in alkaline and acid paper chromatography (»origin material«). Under certain conditions the pancreatin resistant compound can account for over 50 per cent of intrathyroidal iodine. The percentage of labelled origin material increases when the interval between single shot labelling and enzymatic digestion of the gland is extended to several days or weeks. The phenomenon is even more pronounced when the rats are kept on a low iodine diet (LID) during the whole experiment. Furthermore a relative increase of the labelled iodinated material occurs when rat thyroid glands are blocked with a thyrostatic drug or labelled to near isotopic equilibrium instead of short term labelling only. If the rats are kept on LID during the equilibration procedure, the relative concentration of origin material will again exceed that found in the thyroids of the control rats kept on HID. Autoradiography revealed that the centre of a PTU-blocked thyroid gland contains little radioactivity whereas large amounts of labelled colloid remain in the peripheral follicles. Mechanical separation of the peripheral layers from the thyroid core indicates that the enzyme resistant material is located mainly in hypcrplastic follicles. Ultracentrifugation studies have shown that the substance is heterogeneous. A small fraction is sedimented at low centrifugal speed, the bulk, however, remains in the supernatant and is of low molecular weight as shown by sucrose density centrifugation and sephadex gel filtration.

Rat thyroid gland cells were isolated by a trypsinization procedure and cultured for 3 days either in Gelfoam pads in a medium with no TSH or as monolayers in a medium containing 0.17 U of bovine TSH per ml. The cells cultured by the first method were implanted into rats 52-217 days after they had been thyroidectomized by surgical removal of the gland at 20-25 days of age followed by an 131I injection. The cells cultured by the second method were implanted into rats 19 and 20 days after they had been thyroidectomized by an 131I injection on the day of birth. In both cases the implanted cells reorganized into aggregations of follicles containing colloid in their lumens. Autoradiographs of sections of these reformed follicles revealed the presence of protein-bound 131I in the colloid. The implants in both groups of animals utilized radioiodine and formed labeled MIT, DIT, T4 and T3. Iodine metabolism of the implants in the second group of animals was similar to that observed in intact thyroid glands of norm...

PREVIOUS reports from these laboratories1,2 have indicated the thyroid response to thyrotrophic hormone, as measured by uptake of phosphorus-32 (ref. 3), to be increased in sialoadenectomized animals when compared with intact controls. Hypophysectomy and hypophysectomy plus sialoadenectomy gave identical results as regards iodine trapping by rat thyroid, but the ratio of thyroid organic iodine-131 to inorganic iodine-131 indicated that sialoadenectomy reduced the synthesis of organically bound iodine-131 (ref. 4). To date, our observations have indicated some change in the modus operandi of thyrotrophic hormone in animals whose salivary glands have been removed. To obtain further information regarding the role of thyrotrophic hormone in sialex animals, it was decided to investigate the distribution of labelled hormone therein.

Radioactive iodide in the rat thyroid was separated from iodine-containing organic compounds by means of dialysis at 3 C, followed by ion exchange resin chromatography. The thyroid: serum radioactive I- concentration ratio (T:S) one hour after the injection of I131 was much lower when organic binding of I131 was permitted than when it was blocked with propylthiouracil (7 vs. 130); it could be further depressed—to 2– with perchlorate. However, the T:S for binding thyroids rose progressively and eventually exceeded the value determined by giving I131 after propylthiouracil administration; 24–48 hours after the injection of I131, the concentration of radioactive I- in the binding thyroid was no longer diminished by ClO4- nor was it affected by propylthiouracil injected 2 hours before the rats were killed. In rats which were given I131 for 3 weeks to achieve uniform specific activity of iodine throughout the body, 0.26 % of thyroidal iodine was estimated to be in the form of I-; the T:S was 500. It is suggest...

Summary1. Surital markedly reduces the incorporation of I131 into rat thyroid. 2. The proportion of recoverable I131 in the inorganic and organically bound fractions of thyroid alkaline hydrolysate is essentially the same for control and Surital treated rats.

Rat thyroid slices incubated in the presence of radioiodine and thiamine (10–3m) contained less organic radioiodine than control slices. There was no effect of thiamine, however, on the radioiodine content of slices in the presence of propylthiouracil. Thiamine in the diet of rats occasionally inhibited the formation of organic radioiodine compounds but, when augmented by injections of thiamine, inhibition became a consistent finding. There was no goiter formation or increase in the ratio of radiomonoiodotyrosine to radiodiiodotyrosine. It is concluded that thiamine has an antithyroid effect similar to propylthiouracil in inhibiting the formation of monoiodotyrosine although it may not inhibit the later steps in thyroid biosynthesis. (Endocrinology 82:895, 1968)

Hypercalcemia was induced by injecting rats with high daily doses of vitamin D 2 for five days. Thyroid glands from untreated rats were used as controls. The thyroid parafollicular cells of the vitamin-treated rats differed characteristically from those of the controls, the most conspicuous feature of the former being the almost complete degranulation.

SummaryIn vivo depression of I131 uptake by the rat thyroid, and the conversion ratio has been produced by chronic lead intoxication. Female rats are more susceptible than male rats.The authors would like to thank Dr. William J. Darby for his encouragement and suggestions.The opinions are those of the authors and do not necessarily reflect the opinion of the U.S. Navy.

THE cells referred to in this communication were called parafollicular cells by Nonidez1 in dog thyroid. The name was afterwards transferred to cells staining in a similar manner in other species, irrespective of their anatomical position. It was condemned by Stux et al.2 as inaccurate. They substituted the name light cell because, in rat thyroid, the cells are not stained by the periodic acid–Schiff (PAS) method by comparison with the colloid granules of the acinar cells. The name C cell3 was intended to refer to their responsibility for calcitonin secretion, as indicated by cytochemical tests and by immunofluorescence4. It avoids reference to the staining qualities of the cells and to their precise localization, and for this reason it can be applied to all species and to organs and tissues other than the thyroid. Not only are the cells not parafollicular, they are not confined to the thyroid5 and in some species are probably mainly extra-thyroid.

SUMMARY The uptake of 131I by the thyroid of the rat has been investigated under various conditions of stress. The acute change always consists in a considerable reduction of the rate of uptake of 131I irrespective of the nature of the stress. This acute inhibition in the uptake of 131I is independent of the anterior pituitary lobe, since it occurs in the normal and hypophysectomized animal alike. It is also independent of the presence of the adrenals. The inhibition of the uptake of 131I by the thyroids occurs in vivo only; their ability to take up 131I in vitro is not impaired. All the acute changes seen under stress conditions can be readily reproduced by treatment with adrenaline, which shows the same inhibitory effect on normal and hypophysectomized animals, the action being equally transitory. It is suggested that the acute changes in thyroid function seen under stress conditions are entirely independent of the anterior pituitary and are caused by increased release of vasoconstrictor substances. An increased uptake rate of 131I by the thyroid was seen 24 hr after the acute stress. This was thought to be caused by a compensatory increase in the secretion of thyrotrophic hormone by the anterior pituitary.

A comparison of hypophysectomized rats receiving cortisone with similar rats not given corticoid therapy showed that in the former the thyroidal binding of I131 was promoted during the first 16 min after I131 injection. Thyrotropin (TSH) augmented the uptake of I131 by the thyroids of hypophysectomized rats (measured 8 min after I131 injection), but did not improve the efficiency of its organic binding. When such rats were treated with cortisone before TSH was given, the binding of I131 in the thyroid was more efficient. Similarly, intact rats given large doses of cortisone had a higher percentage of thyroidal I131 in the organic form (8 min after the administration of the isotope) than did their untreated counterparts. Cortisone treatment appears to facilitate organic binding of I131 which has entered the thyroid recently.

SummaryIn organ culture of fetal rat thyroid glands, both insulin and TSH enhance significantly the 24 hr incorporation of 125I into protein-bound iodotyrosines and iodothyronines; however, TSH is much more active than insulin. Under the same experimental conditions, although insulin is not so effective as TSH, these two hormones stimulate, in a similar fashion, the iodination of soluble proteins. Both TSH and insulin enhance also the biosynthesis of ribosomal RNAs and of nuclear DNA-like RNAs.The technical assistance of Mrs. Jennequin-Gerbod is gratefully acknowledged.

Goitrogenic response at sequential time intervals after 250 and 500 rads x-rays to the rat thyroid.

Autoradiographs of rat thyroid glands were prepared 1 and 14 days after injection of radioiodide. Follicles could be divided into 2 major classes based on position in the gland and on autoradiographic image density. Most peripheral and isthmic follicles became labeled relatively slowly and retained their label for a relatively long time compared with the remainder of the follicles (central follicles). Exceptional peripheral follicles, mostly those bordering the parathyroid glands, behaved like central follicles. A small fraction of the follicles had unusual autoradiographs 14 days after injection. In addition to dark ring autoradiographs and exceptionally dark images over some small follicles, the unusual images included narrow rings in the interior of lumens, negative rings (images with dark center and pale periphery), and dark images associated with inclusions in the colloid. Exceptional images were interpreted as evidence for follicle growth, spatial heterogeneity of diffusion rates of iodoprotein in i...

The thyroid gland of an animal chronically treated with a thiouracillike drug, although unable to manufacture thyroid hormone, manifests a remarkable ability to collect and concentrate the iodide ion (Vanderlaan and Vanderlaan, 1947; Taurog, Chaikoff, and Feller, 1947). About one hour after the subcutaneous administration of iodide in rats the thyroid exhibits an average concentration gradient of 250 over the serum. Taurog, Chaikoff, and Feller (1947) noted this ratio to be unchanged when 2 μg. or 100 μg. of iodide were given to adult rats. Vanderlaan and Vanderlaan (1947) found that the gradieni, remained constant when doses up to 100 ng. of potassium iodide were administered in young rats, but that when larger quantities were given it diminished progressively. However, even when 10,000 μg. were given the. gradient was not abolished completely, a concentration of 3 fold persisting in favor of the gland.

SUMMARY Rat chromosomes prepared from thyroid cells grown in culture did not differ from those described for other tissues of this species. The incidence of thyroid cells with abnormal chromosomes was not increased by giving propylthiouracil to rats for 15 weeks. The thyroid chromosomes were damaged by injection of 1–25 μc of 131I. The damage persisted in the unstimulated thyroid for 15 weeks. Administration of propylthiouracil to rats after 131I caused significant reduction in the frequency of thyroid cells with radiation-damaged chromosomes.

1) Salivary glands of rats decreased in weight markedly with the administration of thiourea or potassium thiocyanate in drinking water for two weeks and this change was recovered with the intraperitoneal injection of adequate dose of L-thyroxine.2) The effect of chronically partial sialoadenectomy on iodine metabolism of rat thyroid was studied, and no significant change was observed in 40 and 60days after operation.

Radioautographic studies of rat thyroid glands were made at different times after labeling with /sup 125/I and /sup 131/I. Cellular organic radioiodine was demonstrated in the thyroid of an untreated rat after 2-hr labeling with 125. Cellular organic radioiodine was demonstrated in thyroids of rats pretreated with iodide and labeled with /sup 131/I for 10 and 15 min. (auth)

Il trattamento con ATCH o cortisone causa un aumento del contenuto in tirocalcitonina delle tiroidi di ratto. Vengono discusse le possibili implicazioni dei risultati ottenuti.

By means of a micropuncture technique the luminal contents of single rat thyroid follicles were extracted. Analysis of the proteins was performed by micro-disc electrophoresis. The protein composition of the colloid varied between follicles of the same gland. In most follicles 19S thyroglobulin was the predominant protein and in addition 27S and 12S proteins were found in varying relative amounts. In some follicles a 4S protein resembling serum albumin with regard to electrophoretic mobility was observed in addition to the other proteins.

Images Figs. 2-7 Figs. 8-13

SummaryThe adult rat thyroid is established as a system in which mitotic activity is minimal. Recovery from radiation damage is demonstrated in thyroid cells in vivo using split-dose recovery curves and a fractionated-dose survival curve. The results are relevant to radiotherapy and possibly to the theory of recovery.

Measurements of volume of the thyroid, diameter of follicles and height of follicular cells were made under normal or experimental condition of unilateral thyroidectomy in late fetal and newborn rats. During perinatal days, the thyroid did not enlarge, the diameter of follicles was reduced and the height of follicular cells lowered. Unilateral thyroidectomy in fetuses on day 20 of pregnancy caused two days later a significant increase in the ratio of the volume of remaining lobe of thyroid to body weight. The height of follicular cells was increased in a unilaterally thyroidectomized fetus when compared with that in a litter-mate control fetus. In newborn rats, the unilateral thyroidectomy on day 1 of life also caused two days later a significant increase, though less than that observed in fetuses, in the ratio of thyroid volume to body weight. The height of follicular cells was not increased. The observations support the view that in the rat the pituitary-thyroid system begins to function before birth and that the founctioning of the system is slightly reduced just after birth.

G protein-coupled receptor kinases (GRKs) and arrestins are implicated in homologous desensitization of G protein-coupled receptors. We have recently demonstrated that among six GRKs so far identified, GRK5 is the isoform predominantly expressed in the thyroid and appears to be mainly involved in homologous desensitization of thyrotropin receptor (TSHR) in FRTL5 cells. To further understand the molecular mechanisms of the TSHR desensitization, the expression and regulation of GRKs and arrestins together with those of the TSHR were examined in FRTL5 cells. Northern blot analysis of total RNA from FRTL5 cells with the available rat GRK cDNAs (GRK4, 5, and 6) as probes showed that only GRK5 mRNAs of approximately 3, 8, and 10 kilo bases (kb) in length were detectable. When probed with rat beta-arrestin-1 and beta-arrestin-2 cDNAs, beta-arrestin-1 mRNAs of approximately 7.5 and 2.5 kb long, but no (or possibly faint) approximately 2.4 kb beta-arrestin-2 mRNA, were observed, suggesting that in the thyroid, beta-arrestins appear to be predominantly of beta-arrestin-1 isoform. In studies on TSH-regulation of GRK5, beta-arrestin-1 and TSHR mRNAs, steady-state levels of GRK5 and TSHR mRNAs were 3- to 4-fold lower in the cells grown in the medium with TSH than in those without TSH, while betaarrestin-1 mRNA levels were unchanged. Downregulation of GRK5 and TSHR mRNAs by TSH was further confirmed by dose- and time-dependent experiments. Incubation with 1mM 8BrcAMP, a cAMP analog, for 24h fully reproduced this TSH inhibitory effect. A decrease in GRK5 protein by TSH was also confirmed with Western blot analysis. In summary, these data together with our previous data suggested that GRK5 and beta-arrestin-1 seem to be the isoforms predominantly expressed in the thyroid, and they appear to play a pivotal role in TSHR homologous desensitization. We also demonstrated TSH downregulation of GRKS, but not beta-arrestin-1, expression. Further studies will be necessary to elucidate how these phenomena are linked to thyroid pathophysiology.

Thyrotropin-releasing hormone (TRH) synthesized in the hypothalamus has the capability of inducing the release of thyroid-stimulating hormone (TSH) from the anterior pituitary, which in turn stimulates the production of thyroid hormones in the thyroid gland. Immunoreactivity for TRH and TRH-like peptides has been found in some tissues outside the nervous system, including thyroid. It has been demonstrated that thyroid C-cells express authentic TRH, affecting thyroid hormone secretion by follicular cells. Therefore, C-cells could have a paracrine role in thyroid homeostasis. If this hypothesis is true, follicular cells should express TRH receptors (TRH-Rs) for the paracrine modulation carried out by C-cells. In order to elucidate whether or not C-cell TRH production could act over follicular cells modulating thyroid function, we studied TRH-Rs expression in PC C13 follicular cells from rat thyroid, by means of immunofluorescence technique and RT-PCR analysis. We also investigated the possibility that C-cells present TRH-Rs for the autocrine control of its own TRH production. Our results showed consistent expression for both receptors, TRH-R1 and TRH-R2, in 6-23 C-cells, and only for TRH-R2 in PC C13 follicular cells. Our data provide new evidence for a novel intrathyroidal regulatory pathway of thyroid hormone secretion via paracrine/autocrine TRH signaling.

Madin-Darby canine kidney (MDCK) I and Fisher rat thyroid (FRT) cells exhibit transepithelial electrical resistance (TER) values in excess of 5,000 Ω · cm2. When these cells were incubated in the presence of various inhibitors of sphingolipid biosynthesis, a >5-fold reduction of TER was observed without changes in the gate function for uncharged solutes or the fence function for apically applied fluorescent lipids. The localization of ZO-1 and occludin was not altered between control and inhibitor-treated cells, indicating that the tight junction was still intact. Furthermore, the complexity of tight junction strands, analyzed by freeze-fracture microscopy, was not reduced. Once the inhibitor was removed and the cells were allowed to synthesize sphingolipids, a gradual recovery of the TER was observed. Interestingly, these inhibitors did not attenuate the TER of MDCK II cells, a cell line that typically exhibits values below 800 Ω · cm2.These results suggest that glycosphingolipids play a role in regulating the electrical properties of epithelial cells.

The possibility that the iodine supply modulates thyroid lysosomal activity was investigated in rats receiving chronic or acute increasing doses of iodide. The lysosomal activity or the various experimental groups was determined by measuring the activity of β-glycerophosphatase and cathepsin D both in thyroid homogenates and in semipurified thyroid lysosomal preparations, and the degradation of labelled thyroglobulin by the various lysosomal fractions. In the chronic experiments β-glycerophosphatase and cathepsin D activities increased with the iodide supply of the animals up to 100 μg I/rat and decreased slightly thereafter. In the acute experiments the activity of these enzymes increased up to 1000 μg I/rat and decreased above 5000 μg I/rat. The proteolytic activity of lysosomal fractions from the various experimental groups towards thyroglobulin decreased slightly with increased iodide supply both in chronic and acute experiments. The results suggest that thyroid lysosomal activity may participate in the autoregulation of thyroid secretion by inducting synthesis of new enzymes and modulating thyroglobulin degradation.

To investigate the effect of methylthiouracil treatment of rat on protein composition of its I131 labeled thyroid tissue, paper-electrophoresis of its homogenate was performed. The results were as follows : 1) When thyroid was extracted from normal rats 24 hours after the injection of I131, almost all the radioactivity was concentrated at the origin of the paper-electrogram from its homogenate. 2) When thyroid was extracted from methylthiouraciltreated rats 24 hours after the injection of I131, the radioactivity was stronger on the spot about 35 mm from the origin toward the anode than on the origin. 3) When thyroid was extraced from normal rats 2 hours after the injection of I131, the radioactivity on the above described spot was weaker than at the origin.

The activities of an esterase and a protease in thyroid homogenates have been measured. By tissue fractionation, particle extraction and DEAE chromatography the activities have been shown to reside in different proteins. (Endocrinology 77: 415, 1965)

SOME sulphonamide derivatives have been found to have antidiabetic effects, and these drugs have recently been brought into use in the treatment of diabetes1. Sulphonamides are also known to possess goitrogenic properties2. There is some evidence for the goitrogenic effect of the new antidiabetic drug, N1-sulphanilyl-N2-n-butylurea3. In the present communication the effect of this substance on the rat thyroid is described, using histochemically demonstrable succinic dehydrogenase activity of the thyroid gland as an indicator of its activity.

Diasone® Sodium hemmt die Aufnahme von Radiojod in der Schilddruse der Ratte. Diese Wirkung entsteht wahrscheinlich durch Hemmung der Jodid-Peroxydase.

To investigate the effect of shaking on the liberation of iodine containing amino acid from thyroid tissue, I133-labelled rat thyroid homogenate was incubated in incubation medium at 37.5°C about one hour with or without shaking, and then this mixture was investrgated by paperchromatography. The results obtained were as follows : Liberated form of I131-labelled amino acid both in the thyroid homogenate and in the incubation medium were apparently increased by shaking.

Two requirements for the successful preparation of high-resolution autoradiographs are the intimate contact between section and emulsion, and an emulsion-layer which is thin and of sufficiently fine grain. The stripping-emulsion technique was developed by Pelc1 to meet these requirements, and was successfully applied to the location of iodine-131 in rat thyroid. In this technique, section and emulsion are brought into intimate contact under water. Thus it precludes the location of water-soluble tracers; moreover, the use of conventional fixing and dehydrating agents can seriously affect the concentration and distribution of water-soluble tracer in the tissue.

The thyroidal effects of short-lived radioiodines such as /sup 132/I, /sup 133/I, and /sup 135/I have not been well defined. We report here the results of a study comparing the effects of /sup 132/I and /sup 131/I. We found the same effect in goitrogen-stimulated rat thyroid glands (in terms of 50% suppression of thyroid gland weight increase) at injected activities of 93 ..mu..Ci /sup 132/I and 13 ..mu..Ci /sup 131/I. Doses, however, were 3 rad/..mu..Ci /sup 132/I and 194 rad/..mu..Ci /sup 131/I. The same 50% suppression for thyroid dose was found to occur at about 280 rad from /sup 132/I and 2500 rad from /sup 131/I, suggesting an approximately ninefold increase in radiologic effectiveness of /sup 132/I over /sup 131/I.

No significant change occurred in the uptake by the thyroid of male Wistar rats of a standard dose of carrier-free 1311 administered intraperitoneally and its retention by the thyroid, as measured by biological and effective half-life, after feeding these rats a powdered pelleted diet containing lithium carbonate (I . I g per kg of diet) for 7 days. However, continuing this diet for 10 days inhibited thyroid uptake and increased the retention of 131 I. Uptake remained suppressed for up to 4 months after lithium treatment and continuing this treatment for 6 months did not result in any significant change in 1311 uptake by the thryoid. Lithium treatment for 10 days increased the biological and effective half-life of 13l I in the thyroid and this increase continued for the 6 months treatment period. The dose of 13l I delivered to the thyroid was significantly lower after 10 days and I month of lithium treatment but there was no change in this dose after 2 and 4 months of treatment. However, there was a significant increase after 6 months.

An accurate method of thyroid /sup 131/I dosimetry was developed by imploying the dose formulation recommended by the Medical Internal Radiation Dose (MIRD) Committee. Six-week-old female Long-Evans rats were injected intraperitonealy with 0.5, 1.9, and 5.4 ..mu..Ci of Na/sup 131/I. The accumulated /sup 131/I activities in the thyroid were precisely determined by integrating the /sup 131/I activities per gram of the thyroid as functions of postinjection time. When the mean thyroid doses derived from this method are compared to those derived from the conventional method, the conventional method over-estimated the doses by 60 to 70%. Similarly, the conventional method yielded effective half-lives of 2.5 to 2.8 days; these estimates were found to be high by factors of 1.4 to 2.0. This finding implies that the biological elimination of iodide from the rat thyroid is much more rapid (up to 2.5 times) that once believed. Results from this study showed that the basic assumption in the conventional method of thyroid /sup 131/I dosimetry in the rat, i.e., that the thyroid iodide retention function is a single exponential, is invalid. Results from this study also demonstrated that variations in animal body weight of 6 to 7-week-old animals and diurnal variation have nomore » significant influence on the mean thyroid doses for a given injected activity of /sup 131/I. However, as expected, variation in iodide content of the animal diets significantly altered the thyroid doses for a given /sup 131/I injected activity.« less

SUMMARY 1. The cytochemical localization and changes of various phosphatase activities were studied in rat thyroid and anterior pituitary glands in various phases of secretory activity. The procedures used, made possible light microscopic study of the Golgi apparatus, plasma membranes and sinusoids, lysosomes, endoplasmic reticulum, nuclei and nucleoli; reactive sites many of which up to the present were in the realm of ultrastructure and could only be visualized with very specialized techniques or the electron microscope. The enzymatic make up and changes, and changes in size, shape and distribution of these structures were also studied in the conditions described. 2. Nucleoside phosphatase techniques visualized sinusoids, but this staining did not vary with secretory activity. The alkaline phosphatase procedure did not stain sinusoids of the anterior pituitary. However, the sinusoidal staining of the thyroid with this technique paralleled secretory activity. 3. Thiamine pyrophosphatase, inosine diphosphatase and guanosine triphosphatase staining visualized the Golgi lamellae in the two glands and this staining paralleled secretory activity. The adenosine monophosphatase technique stained occasional Golgi lamellae. 4. The adenosine monophosphatase procedure stained the plasma membranes of the less active cells of the anterior pituitary and granular cytoplasmic particles (lysosomes) of more active pituitary and thyroid cells. This granular cytoplasmic staining was abolished by sodium fluoride and d-tartaric acid as was acid phosphatase staining. 5. The inosine diphosphatase and guanosine triphosphatase techniques also revealed some diffuse cytoplasmic and cell membrane staining which was thought to represent staining of endoplasmic reticulum. 6. The adenosine diphosphatase procedure invariably stained nuclei and nucleoli.