Effect of triiodothyronine treatment, thyroparathyroidectomy and mercaptoiminazole treatment on enchondral bone growth. Changes in the histological structure of the growth organ.

Histological changes caused by triiodothyronine (T3) and mercaptoiminazole treatment as well as by thyroidectomy have been studied in the proximal growth organ of the tibia of growing rats. On triiodothyronine treatment morphometric examinations revealed an increased proliferation and resorption of cartilage associated with a transitory acceleration of linear bone growth. Administration of mercaptoiminazole and thyroidectomy inhibited cartilage proliferation and resorption resulting in a slowing down of bone growth.     

Delayed equilibrium of pituitary triiodothyronine (T3) following an acute T3 administration.

To reconcile the knowledge on tissue T3 concentration with cellular metabolism regulatory mechanism of thyroid hormone secretion, the pattern of the change of tissue T3 concentration following an acute administration of T3 was studied in mice. Basal T3 concentration in serum, liver, brain and pituitary was 61, 173, 198 and 1630ng/100g, respectively. After 0.5 mug T3 dose, T3 concentration in serum and liver reached the maximum level 1 to 3 hrs following the administration and decreased exponetially thereafter, thus, maintaining almost constant tissue/plasma T3 ratio. In contrast, T3 increase in brain or pituitary was far delayed, not until 7 to 12 hrs following T3 injection, and then decreased parallel to that in serum. Furthermore, the magnitude of increase in pituitary T3 was limited when compared to that in liver. Thus, tissue/plasma T3 ratio in pituitary decreased markedly after the dose of T3. This finding suggests the possibility that there is blood-brain barrier or blood-tissue barrier for the transport of T3 in pituitary or brain, resulting in delayed equilibrium with that in serum. These results may also explain the delay of inhibition of TRH-induced TSH release after single dose of T3 as recently reported by Azizi et al. (1975).     

Effect of triiodothyronine (T3) on ribonucleic acid polymerase activity in developing tadpole hindlimb

Optimum conditions were studied for the determination of RNA polymerase activity in nuclei isolated from Rana catesbeiana tadpole hindlimbs. Tadpole nuclei were tested at 15 degrees C in the presence of spermidine (1.5 mM) bovine serum albumin (1.0%) and a high concentration of nucleoside triphosphates (1.0 mM). Tadpole nuclei exhibited a 60-70% higher total RNA polymerase activity with maximum activity of RNA polymerase I at 4 hr and RNA polymerase II at 8 hr after triiodothyronine injection. The results support a nuclear mechanism for the differentiation of tadpole hindlimbs induced by triiodothyronine.     

Effect of maternal thyroparathyroidectomy before gestation on fetal development in rats.

Female rats were thyroparathyroidectomized (TPTX) at 24 (immature), 40 (pubertal) and 75 (matured) days of age, at least 21 days before mating. Thyroxine (2.5 microgram/kg) or parathyroid hormone (150 USP units/kg x 2) was replaced in two TPTX groups. Thyroxine deficient groups of all ages had reduced body weight, litter size and serum thyroxine and calcium level. Fetal weights at 20 days of gestation in all thyroxine deficient groups were significantly reduced but placental weight was generally increased. Maternal serum thyroxine and fetal weight was positively related when all groups were taken together, but maternal serum calcium and fetal weight was not related. There were no significant differences in gross, visceral or skeletal anomalies in the fetuses in any group.     

Effect of the inhibition of triiodothyronine (T3) production by thiamazole on the T3 and serotonin content of immune cells

Triiodothyronine (T3) and serotonin are present in the cells of immune system (blood, peritoneal and thymic lymphocytes, monocytes and granulocytes of the blood and peritoneal fluid, mast cells). In the present experiments the effect of thiamazole, an antithyroid drug was studied on the content of these two hormones in immune cells after one and two weeks of continuous treatment (by drinking water, containing 30 mg/100 ml thiamazole, ad libitum) in adult male rats, using flow cytometric and confocal microscopic analysis. In thymic lymphocytes both hormone contents significantly increased in both time points. A significant decrease of T3 was observed in peritoneal monocytes and granulocytes also in both time points, in peritoneal mast cells after one week and in blood lymphocytes after two weeks. Serotonin content in addition to the elevated thymic values (in both measurements) was significantly reduced in blood lymphocytes after two weeks. Confocal microscopy demonstrated heterogeneous cell populations with disparate hormone content and mostly diffuse localization The experiments call attention to the presence of T3 in the immune cells and to its variable concentration under the effect of a thyrostatic drug as well, as to the T3-serotonin relationship in the cells of the immune system.     

Thyrotropin (TSH) regulates triiodothyronine (T3) production in the unicellular Tetrahymena

The aim of the experiments was to study the regulation of triiodothyronine (T3) production in the unicellular Tetrahymena. Untreated and troph-hormone treated specimen were prepared and in different timepoints T3 content was measured and compared by immunocytochemical flow cytometry. 0.1 or 0.001 IU TSH in tryptone-yeast medium stimulated T3 synthesis at 10, 20, 30 min, but does not stimulate after 1 h. The overlapping gonadotropic hormone (GTH) also did it, however only at 10 min. In Losina salt solution (physiological for Tetrahymena) the effect was weaker, however outer amino acid source was not absolutely needed for the production of the hormone. The results show that the TSH regulation of thyroid hormone synthesis (storage, secretion) and troph-hormone overlap can be deduced to a unicellular level. This may allow the hypothesis that the endocrine mechanisms proved at a low level of phylogeny are preserved for the higher ranked organisms.     

Dexamethasone counteracts the immunostimulatory effects of triiodothyronine (T3) on dendritic cells

Glucocorticoids (GCs) are widely used as anti-inflammatory and immunosuppressive agents. Several studies have indicated the important role of dendritic cells (DCs), highly specialized antigen-presenting and immunomodulatory cells, in GC-mediated suppression of adaptive immune responses. Recently, we demonstrated that triiodothyronine (T3) has potent immunostimulatory effects on bone marrow-derived mouse DCs through a mechanism involving T3 binding to cytosolic thyroid hormone receptor (TR) β1, rapid and sustained Akt activation and IL-12 production. Here we explored the impact of GCs on T3-mediated DC maturation and function and the intracellular events underlying these effects. Dexamethasone (Dex), a synthetic GC, potently inhibited T3-induced stimulation of DCs by preventing the augmented expression of maturation markers and the enhanced IL-12 secretion through mechanisms involving the GC receptor. These effects were accompanied by increased IL-10 levels following exposure of T3-conditioned DCs to Dex. Accordingly, Dex inhibited the immunostimulatory capacity of T3-matured DCs on naive T-cell proliferation and IFN-γ production while increased IL-10 synthesis by allogeneic T cell cultures. A mechanistic analysis revealed the ability of Dex to dampen T3 responses through modulation of Akt phosphorylation and cytoplasmic-nuclear shuttling of nuclear factor-κB (NF-κB). In addition, Dex decreased TRβ1 expression in both immature and T3-maturated DCs through mechanisms involving the GC receptor. Thus GCs, which are increased during the resolution of inflammatory responses, counteract the immunostimulatory effects of T3 on DCs and their ability to polarize adaptive immune responses toward a T helper (Th)-1-type through mechanisms involving, at least in part, NF-κB- and TRβ1-dependent pathways. Our data provide an alternative mechanism for the anti-inflammatory effects of GCs with critical implications in immunopathology at the cross-roads of the immune-endocrine circuits.     

Sexual dimorphism for growth in Muscovy ducks and changes in insulin-like growth factor I (IGF-I), growth hormone (GH) and triiodothyronine (T3) plasma levels.

Muscovy ducks display marked sexual dimorphism for body weight. The aim of our study was to analyse the possible relationships between this dimorphism and plasma levels of T3, GH and IGF-I from hatch to 15 weeks of age. We found no significant effect of sex or age on plasma T3 which remained relatively stable about 6 nM x L(-1). Plasma GH levels were highest (14-24 ng x mL(-1)) but highly variable during the first four weeks in females and during the first seven weeks in males. Then, they decreased and remained low (3-4 ng x mL(-1)) until the age of 15 weeks. A trend for higher GH concentrations in males compared to females was observed across the experimental period. The difference was maximum around 6-7 weeks of age. Plasma IGF-I levels rose sharply between 2 and 3 weeks of age and remained high until 6-7 weeks of age for the females and 13 weeks of age for the males then started to decrease. For the whole experimental period, significantly higher IGF-I levels were measured in males. The differences between sexes were significant between 7 and 12 weeks of age and at 14 weeks of age. The differences in circulating GH and IGF-I levels between sexes suggest that the somatotrophic axis is implicated in Muscovy duck sexual dimorphism.     

Characterization of canine triiodothyronine (T3) autoantibodies and their effect on total T3 in canine serum

A study of 3,5,3'-L-triiodothyronine autoantibody (T3 AA) in 18 dogs revealed an average apparent affinity constant for T3 of 2.24 +/- 1.78 X 10(10) M-1, an average T3 binding capacity of 639.3 +/- 666.5 ng/dl and a low thyroxine (T4) cross-reactivity (less than 1%) in all samples tested. A valid radioimmunoassay (RIA) procedure which involved heat treatment of samples for 1 hr at 70 degrees C and assay on Sephadex minicolumns was developed for measuring T3 in the presence of T3 AA. Total T3 was elevated (mean = 374.8 +/- 158.4 ng/dl) in samples in which T4 was in the normal canine range, but T3 was lower (mean = 96.1 +/- 63.3 ng/dl) in samples with T4 values in the hypothyroid range. For each sample the concentration of T3 not bound by T3 AA was calculated from the total T3 concentration, the affinity constant, and the binding capacity. In dogs with normal total T4 concentrations the average calculated T3 not bound by T3 AA was 147.2 +/- 144.4 ng/dl while in dogs with low total T4 the value was 15.7 +/- 26.3 ng/dl (normal canine range is 45-150 ng/dl). Canine samples containing T3 AA were compared to serum from three rabbits actively immunized against T3 to provide anti-T3 for commercial RIA. The rabbit T3-antisera had an average T3 affinity constant similar to those of the canine samples (1.57 X 10(10) M-1), but had average titer, T3 binding capacity, and total T3 values more than 10-fold higher. Our findings indicate that, in dogs with serum containing T3 AA and normal total T4 concentrations, a compensatory mechanism appears to exist to maintain non-T3 AA bound T3 within the range of normal total T3. This compensatory mechanism does not operate in those dogs with insufficient thyroid activity to maintain normal total T4 values.     

大鼠脑穹窿下器官微量注射AngⅡ对肾近球小管Na+,K+-ATPase功能的影响

目的：探讨大鼠穹窿下器官（SFO）对外周肾小管钠泵的调节作用及机制。方法：在SFO分别微量注射血管紧张素II（AngII）,其中氯沙坦（losartan）组先用AngII的1型受体（AT1）拮抗剂losartan预处理后再注射AngII 放免法检测血清中内源性洋地黄样物质（EDLS）的水平和血浆AngII水平 微分离大鼠肾脏单根近球小管,液闪法测定小管管周膜钠泵活性。结果：①SFO注射AngII后,血清中EDLS在15 min开始升高,约60 min达高峰 ②肾近球小管钠泵活性在SFO注射AngII后30 min和60 min都显著下降 ③用losartan预处理SFO后,再注射AngII,血清EDLS水平升高和小管钠泵活性下降的效应被显著削弱。结论：大鼠SFO注射AngII后,肾近球小管钠泵活性将下降,原因可能与SFO注射AngII后,激动SFO的AT1受体,直接或间接升高血清EDLS水平有关。     

Presence of nuclear triiodothyronine (T3) receptors in mouse fibroblasts]

The present preliminary data obtained from intact fibroblasts of adult mice (polyploid stem L 929) suggest that this cell system possesses high-affinity and saturable nuclear binding sites for triiodothyronine. As estimated by the Scatchard analysis, the equilibrium dissociation constant is approximately 2 X 10(-10) moles, the maximal binding capacity is about 2 000 sites for T3 per cell nucleus.     

Importance of the excretion of triiodothyronine (T3) in normal infants and children

Serum concentrations of thyroxine (T4) and triiodothyronine (T3) are higher in normal neonates and children than in adults, having a thyroxine to triiodothyronine ratio close to 50. T3 excretion is almost as high as that of T4 (T4 to T3 ratio from 0.6 to 0.8 in children). This amount of excreted T3 represents a loss of about 1/10 of the theoretical daily production rate of the hormone.     

Effect of simultaneous administration of betamethasone and triiodothyronine (T3) on the development of functional pulmonary maturation in fetal rabbit

Recent experimental evidence suggests that a combination of glucocorticoid and thyroid hormone may be more effective than either hormone alone in accelerating morphologic as well as biochemical mammalian fetal lung maturation. We have demonstrated that IM administration of T3 to the rabbit doe is associated with enhanced functional fetal lung maturation. We investigated the effect of simultaneous administration of T3 and betamethasone on the development of functional fetal lung maturation and the duration of survival after premature delivery. On day 25 and 26 of pregnancy, T3 (175 micrograms/kg/dose) betamethasone (85 micrograms/kg/dose), T3 plus betamethasone or the appropriate amount of the vehicles were injected. The functional fetal pulmonary maturity and the duration of survival after premature delivery were assessed on day 27 of gestation. Although enhanced functional fetal lung maturation was observed after T3 or betamethasone administration, there was no additive effect after simultaneous administration of both. The duration of survival on premature delivery was enhanced in betamethasone but not T3 or T3 plus betamethasone group when compared to control. Further animal experimentation seems necessary before a clinical trial of T3 plus betamethasone therapy is considered.     

1,25(OH)2D3 alters growth plate maturation and bone architecture in young rats with normal renal function

Whereas detrimental effects of vitamin D deficiency are known over century, the effects of vitamin D receptor activation by 1,25(OH)(2)D(3), the principal hormonal form of vitamin D, on the growing bone and its growth plate are less clear. Currently, 1,25(OH)(2)D(3) is used in pediatric patients with chronic kidney disease and mineral and bone disorder (CKD-MBD) and is strongly associated with growth retardation. Here, we investigate the effect of 1,25(OH)(2)D(3) treatment on bone development in normal young rats, unrelated to renal insufficiency. Young rats received daily i.p. injections of 1 μg/kg 1,25(OH)(2)D(3) for one week, or intermittent 3 μg/kg 1,25(OH)(2)D(3) for one month. Histological analysis revealed narrower tibial growth plates, predominantly in the hypertrophic zone of 1,25(OH)(2)D(3)-treated animals in both experimental protocols. This phenotype was supported by narrower distribution of aggrecan, collagens II and X mRNA, shown by in situ hybridization. Concomitant with altered chondrocyte maturation, 1,25(OH)(2)D(3) increased chondrocyte proliferation and apoptosis in terminal hypertrophic cells. In vitro treatment of the chondrocytic cell line ATDC5 with 1,25(OH)(2)D(3) lowered differentiation and increased proliferation dose and time-dependently. Micro-CT analysis of femurs from 1-week 1,25(OH)(2)D(3)-treated group revealed reduced cortical thickness, elevated cortical porosity, and higher trabecular number and thickness. 1-month administration resulted in a similar cortical phenotype but without effect on trabecular bone. Evaluation of fluorochrome binding with confocal microscopy revealed inhibiting effects of 1,25(OH)(2)D(3) on intracortical bone formation. This study shows negative effects of 1,25(OH)(2)D(3) on growth plate and bone which may contribute to the exacerbation of MBD in the CKD pediatric patients.     

Investigations on the triiodothyronine (T3)-specificity of thyrotropic (TSH) and gonadotropic (HCG) hormone in the unicellular Tetrahymena

In a previous experiment thyrotropin (TSH) increased the triiodothyronine (T3) production of Tetrahymena and chorionic gonadotropin (HCG) moderately overlapped the effect. At present the production of three amino acid type (histamine, serotonin, epinephrine) and one peptide (endorphin) hormones were studied under the effect of TSH or HCG, in tryptone-yeast (TY) or salt (Losina-Losinsky) medium. The duration of the effect was 10 min. TSH significantly (with almost 20%) decreased epinephrine production in TY medium and HCG similarly decreased epinephrine and increased histamine level. In salt solution TSH as well as HCG decreased the level of serotonin. The results show that at this low level of phylogeny TSH effect is not completely thyroxine-specific, however it is not general. HCG overlaps TSH effect on epinephrine and serotonin production, however its effect is broader. The experiments also demonstrate that the effect of pituitary trop-hormones can be bidirectional in Tetrahymena, as histamine level was increased and epinephrine level was decreased by HCG, in the same cells.