Depletion and reaccumulation of follicular thyroglobulin (TG) in guinea-pig thyroid gland after short- and long-term administration of thyrotropin (TSH).

The relationships among the content and composition of soluble iodoproteins in thyroid gland, the serum Tg concentration and the morphological structure of gland were investigated in guinea-pigs during short-term and long-term TSH administration (2 I.U. per day for 1 to 28 days). A significant decrease in the content of Tg in the gland (from 6.50 mg to 1.32 mg/100 mg tissue), disappearance of 12 S iodoprotein, hypertrophy and hyperplasia of the follicular cells were observed in guinea-pigs treated with TSH up to 7 days. Later on, after depletion of follicular colloid, reaccumulation of colloid in the preexisting and newformed follicles (a marked increase of Tg and 12 S protein) and partial involution of the structural changes occurred. The serum Tg concentration increased during the whole period of TSH treatment (mean values from 100 to 500 micrograms/l). A marked positive correlation between serum Tg concentration and thyroid weight was found. Serum T3 and T4 concentrations increased transiently with maximal values on the 1st day (T3, from 0.86 to 3.26 nmol/l, T4, from 44 to 138 nmol/l) and decreased thereafter. The results imply that different regulatory mechanisms exist which control thyroid hormone secretion and transfer of Tg from the gland into blood circulation. The serum Tg level is directly dependent on the total bulk of thyroid tissue, but is considerably less dependent on the structure of the gland. The reaccumulation of colloid (Tg) in thyroid follicles of guinea-pigs treated with TSH is a result of the reduction of the stimulatory effect of TSH on the process of Tg degradation during chronic hormone application. Several different factors may be responsible for the appearance of refractoriness or desensitization of the thyroid to prolonged exogenous TSH stimulation.

Susceptibility to proteolysis of thyroglobulin from rats and guinea-pigs treated with excess iodide.

The effect of excess iodide on proteolysis of in vivo 125I-labelled thyroglobulin (Tg) from rats and guinea-pigs was investigated in vitro using preparations of thyroid lysosomes and exogenous proteases (Pronase). Lysosomes were obtained by centrifugation of pig thyroid homogenates. This lysosomal preparation induced maximal proteolysis of Tg at pH 3.6 to 4.6 and was stimulated by KCl. Treatment of rats with excess iodide for up to 28 days had no effect on the proteolysis of Tg by lysosomes or Pronase. Decreased resistance of Tg to proteolysis by lysosomes and pronase was observed in guinea-pigs treated with excess iodide for 3 days, whereas Tg from guinea-pigs treated for longer time periods had increased resistance to proteolysis. This difference in the susceptibility to proteolysis of Tg provides an explanation why long-term administration of excess iodide is goitrogenic in guinea-pigs but not in rats.

[Importance of determining gonadotropin levels in the serum in secondary amenorrhea]. / Znacaj odredivanja nivoa gonadotropina u serumu zena sa sekundarnom amenorejom.

On the basis of the results of the analysis of FSH, LH, and prolactin values in the serum of patients with secondary ammenorrhea, four groups of patients were formed: group 1 with low values of both gonadotropin hormones, group 2 with low FSH and high LH values, group 3 with high FSH and high LH values, and group 4 with the basdal gonadotropin values within normal. The use of functional tests proved helpful in the differentiation of the causes of amenorrhea. The use of the LH-RH test is of particular significance in the differentiation of the degree of changes in patients from group 1 and 4. To determine adequate therapy, the determination of estrogen in patients from group 1 and 3 is imperative. A successful treatment of secondary amenorrhea depends on its duration and a timely detection of its causes.

Some disturbances related to iodination and utilisation of thyroglobulin and 27 S iodoprotein in non-toxic multinodular goitre.

The relationships among the thyroid iodoproteins, their biosynthesis in vitro in thyroid slices and the histological structure of a multinodular, sporadic goitre was examined after strumectomy from a euthyroid 51-year-old woman. Using sedimentation methods 27S, thyroglobulin (TG), 12S and 3--8S proteins were found. Besides these, 4 to 5 other proteins with molecular weights between 165,000 and 36,000 daltons were detected by polyacrylamide gel electrophoresis. The concentration of soluble proteins was very low (3 mg/100 mg wet tissue), particularly TG (0.69 MG/100 MG). The sedimentation constant (18.3S) of goitrous TG was lower than mature 19S-TG and it was poorly iodinated (0.06% w/w). 27S iodoprotein was present in the goitre extract. Thyroid slices of goitre tissue incorporated 14C-leucine into proteins and synthesized TG and its subunits. Newly synthesized proteins were rapidly released from the microsomes. Pathohistologically, struma colloido-microfolliculare with dystrophic-proliferative changes was noted. In the large follicles which were filled with colloid, dystrophic alterations in thyrocytes and desquamation of the follicular epithelium were observed. In conclusion, it is suggested that the presence of poorly iodinated, immature TG in nontoxic multinodular, sporadic goitre, in the absence of iodine deficiency, probably results in disturbances in the utilization of TG from the follicular lumen. In the follicular lumen under these conditions it is possible that 27S protein is formed from pre-existing poorly iodinated TG. These findings suggest that inability to resorb colloid may be a cause of nodule formation.

Effect of prostaglandin PGE2alpha on the synthesis of placental proteins and human placental lactogen (HPL).

The biosynthesis of placental proteins and placental lactogen (HPL) was studied in vitro in 10-12 week, 16-18 week and term human placenta in the presence and absence of PGF2alpha. The highest 14C-leucine incorporation was detected in 10 to 12 weeks old placentas of PGF2alpha to the incubation medium depressed the rate of incorporation of 14C-leucine into placental proteins in a dose dependent manner. Placentas most sensitive to this action of PGF2alpha were those obtained at 18 weeks of gestation followed by placentas at term. In vivo application of PGF2alpha for therapeutic induction of abortions resulted in the marked inhibition of placental protein synthesis in vitro.

Relationship of biochemical and morphological changes in rat thyroid and proton spin-relaxation of the tissue water.

The effect was studied of biochemical and morphological changes induced by antithyroid substances (PTU, C10(-4)) on proton spin-relaxation properties of rat thyroid gland. It was found that thyroid stimulated by PTU (0.05%) or C10(-4) (1.0%) exhibit marked morphological changes (hyperplasia and epithelial hypertrophy) with alteration of the soluble iodoprotein pattern (content and composition.). Both relaxation times spin-lattice (T1) and spin-spin (T2) were increasing with the lenght of treatment with antithyroid drugs. Reversibility of the process was noted in accordance with biochemical and morphological data. The relaxation rate (formula: see text) for thyroid tissue water was in positive correlation with the suluble protein concentration and particularly with the TG content in the gland. There was no difference in relaxation times between normal thyroid and gland of rats treated chronically with excess iodide. The observed difference in T1 between normal glands and glands of PTU,-C10(-4)--treated rats was comparable with that found in cases of human thyroid cancer. This finding is of importance when the diagnostic potential of NMR in the detection of malignancy is considered. In conclusion, a strong correlation was found between microstructural and biochemical changes of the thyroid gland and proton magnetic relaxation of tissue water. The striking difference between the proton spin-relaxation times in normal and in goiter thyroid glands of rats suggests that pulsed NMR spectroscopy could be a method for evaluation of some disturbances in thyroid gland.

Dynamics of biosynthesis of thyroglobulin subunits and their polymerization in rabbit thyroid slices in vitro.

The dynamics of biosynthesis and aggregation of subunits into thyroglobulin (TG) was studied in vitro in rabbit thyroid slices incubated from 5 to 300 min in the presence of I-14C leucine. The incorporation of labelled amino acid was followed in total soluble and microsome-bound proteins, as well as its distribution in soluble protein fractions. The incorporation of lebelled amino acid into soluble and microsome-bound proteins increased with time of incubation. The analysis of individual soluble proteins indicated that the label was incorporated very early, not only into 3--8S, but also into a protein which corresponds to the 12S fraction. Maximal incorporation into 12S protein was achieved after 60 min of incubation and then the intensity of incorporation decreased, followed by an increase in the relative and absolute amount of TG. The appearance of 14C-leucine in the TG region was not observed before 30 min of incubation. The dynamics of incorporation of 14C-leucine into thyroid proteins indicates very rapid transformation of newly synthesized 12S subunits into TG. After two hours of incubation the newly synthesized TG already showed the same sedimentation properties as pre-formed rabbit TG or native rat 19S TG-125I thus demonstrating that maturation, similar to polymerization, is a very rapid process, i. e. the newly formed TG is quickly transformed into its mature form. Our previous studies and the results presented in this work suggest that 12S protein may also have a precursor character. The presence of 12S protein in thyroid extract is not always the result of dissociation of TG, but also a consequence of polymerization of the basic subunits of TG.