Immunohisto- and immunocytochemical studies on the dynamics of TSH and GTH cells in normally metamorphosing, metamorphosed, and metamorphosis-arrested Hynobius retardatus

The development and dynamics of TSH and GTH cells were studied immunohisto- and immunocytochemically in the salamander Hynobius retardatus, which had been reported to show neoteny in a specific environment and a precocious development and maturation of testis in goitrogen-treated larvae. Pituitary glands from normally metamorphosing and metamorphosed animals, and metamorphosis-arrested larvae which had been treated with goitrogens, were examined using anti-human TSH beta and anti-bullfrog LH beta sera. The immunoreactive TSH cells in the goitrogen-treated larvae began to exceed those in the controls in number at 40 days after hatching (stage 64). At the end of this experiment (220 days after hatching), the goitrogen-treated larvae had four times more immunoreactive TSH cells than the controls. The immunoreactive TSH cells in the goitrogen-treated larvae came to occupy nearly the whole area of the section of the pars distalis. Contrary to this, no significant differences were observed in the number of immunoreactive GTH cells between the goitrogen-treated larvae and the controls during their ontogeny. The number of immunoreactive GTH cells was much less than that of immunoreactive TSH cells. Immunocytochemistry at the electron microscopical level revealed many "thyroidectomy cells" with extraordinarily inflated ER and secretory granules which showed strong immunoreactivity with anti-TSH beta antibody only in the pars distalis of the goitrogen-treated larvae. These results suggest the possibility that TSH induces precocious testicular development and maturation in the goitrogen-treated larvae in H. retardatus.

Effect of thyroid hormones on pituitary neuromedin B and possible interaction between thyroid hormones and neuromedin B on thyrotropin secretion

Neuromedin B (NB), a bombesin-like peptide, has been recently characterized as a physiological paracrine/autocrine inhibitor of thyrotropin (TSH) secretion. We hypothesized on the basis of our prior experiments that thyroid hormones stimulate pituitary NB secretion which mediates, at least in part, the TSH-suppressive effect of thyroid hormone. Here, we evaluated the time-course of the effect of thyroid hormones administration to eu- and hypothyroid rats on the anterior pituitary content of NB and on serum TSH. As previously reported, the pituitary content of NB increased in hyperthyroidism and decreased in hypothyroidism. Chronic treatment of hypothyroid rats with a physiological dose of thyroxine (0.8 microgram/100 g b.w. s.c, for 3 or 5 days) normalized pituitary NB content, while 5 days of treatment with a pharmacological dose of thriiodothyronine (0.4 microgram/100 g b.w.) induced an increase above that of normal pituitaries. Thyroxine and triiodothyronine injected once, s.c., into hypothyroid rats required 30 min to normalize NB content, which reached higher than normal values in 3-6 h. At these times, the increment in NB preceded or was simultaneous with the suppression of serum TSH. This rapid and marked effect on pituitary neuromedin B content, associated in time with TSH suppression, is in agreement with the hypothesis that neuromedin B may mediate at least in part, the acute suppression of TSH release by thyroid hormone, a hypothesis that still needs further verification.

Identification and characterization of novel genes modulated in the thyroid of dogs treated with methimazole and propylthiouracil

Induction of cell proliferation by mitogen or growth factor stimulation leads to the specific stimulation or repression of a large number of genes. To better understand differentiated epithelial cell growth regulation, we have initiated a study to identify genes which are regulated by the thyrotropin-dependent mitogenic pathway in dog thyroid cells. A thyroid cDNA library was prepared from a methimazole and propylthiouracil-treated dog and differentially screened with probes derived from control or stimulated thyroids. Among 19 clones isolated, 6 encode known proteins (inwardly rectifying potassium channel, nucleosome assembly protein, ribosomal protein L7, elongation factor 1alpha, non-muscle myosin light chain, and heat shock protein 90beta). The 13 others correspond to proteins whose function is unknown. Among them, 5 correspond to mRNAs whose expression was modulated by mitogenic stimulation of thyrocytes in primary culture. A preliminary characterization of two of these cDNAs is reported: clone 5, which might represent a novel, atypical protein kinase, and clone 3, which contains ankyrin-like repeats, suggesting that it might interact with other proteins.

Effect of rearing temperature on perirenal adipose tissue development and thermoregulation following methimazole treatment of postnatal lambs

This study examined the effect of ambient temperature on perirenal adipose tissue development and thermoregulation over the first month of postnatal life in lambs treated with a drug that reduces thyroid hormone synthesis (methimazole; at a dose of 50 mg day-1 (kg body weight)-1). Twin lambs were hand-reared at a fixed level of nutrition in either a warm (WR; 25 degrees C) or cool (CR; 10-15 degrees C) ambient temperature. Oxygen consumption, heart rate and colonic temperature were measured during non-rapid eye movement sleep in different ambient temperatures (6, 15, 25 and 34-36 degrees C) at 7, 14 and 28 days of age. Plasma thyroid hormone concentrations decreased with postnatal age and were higher in CR than in WR lambs. All lambs increased plasma thyroid hormone concentrations and O2 consumption during cold exposure but this was associated with a mean increase in colonic temperature in WR lambs at 7 or 28 days. Colonic temperature increased with the onset of panting at all ages when lambs were exposed to 34-36 degrees C, a response that was greatest at 28 days in CR lambs. An increase in colonic temperature with age was observed in CR but not WR lambs. Heart rate declined with age only in the WR group. At 8 and 29 days there were no significant differences between WR and CR groups in the occurrence of shivering or in the thermogenic activity (i.e. GDP binding to mitochondria) of perirenal adipose tissue. At 29 days WR lambs possessed more adipose tissue with a higher lipid and DNA content. It is concluded that modest changes in rearing temperature can have a large influence on the control of body temperature and thyroid hormone response to methimazole treatment. CR lambs are able to maintain higher plasma thyroid hormone concentrations and exhibit improved thermoregulation compared with WR lambs without any detectable differences in brown adipose tissue function.

Preoperative treatment of intractable hyperthyroidism with acute lithium administration

We present a 15-year-old girl with an unusual clinical course of intractable thyrotoxicosis that was resistant to thiocarbamide therapy and propranolol. Although the latter beta-adrenergic blocking agent has been used as the sole drug in the preparation of thyrotoxicosis patients for thyroidectomy, it was unsatisfactory for control of our case. In contrast, the patient's clinical response to lithium carbonate 900-1500 mg/d for 10 days was very good and no side effects were observed. This demonstrates the importance of lithium as the drug of choice in thyrotoxic emergencies and uncontrolled preoperative patients when rapid and safe inhibition of thyroid hormone secretion is required.

Effects of transient prepubertal 6-N-propyl-2-thiouracil treatment on testis development and function in the domestic fowl

It has been well established that thyroid hormones play an important role in regulating the onset of puberty and reproductive function in birds. In mammals it has been shown that transient hypothyroidism induced with the reversible goitrogen 6-N-propyl-2-thiouracil (PTU) can result in tremendous increases in testis size and sperm production and that the timing of hypothyroidism must correspond to the period of Sertoli cell proliferation. As the period of Sertoli cell proliferation is not precisely known in the fowl, an experiment was conducted to determine whether chicken testes have a similar window of sensitivity to PTU treatment. Broiler breeder male chicks (Peterson) were placed in floor pens at one day of age and reared according to the breeder's management guide for the entire 28-wk duration (controls) or up to the point of dietary treatment with PTU (0.1% w:w) for 6 wk that began at 2-wk intervals (2-8, 4-10, 6-12, 8-14, and 10-16 wk of age); after treatment, birds were returned to feed restriction and photostimulated at 20 wk of age. Birds were bled and killed, and testes were collected at 4-wk intervals. At 28 wk, one testis was fixed for histological examination and one was immediately placed in liquid N2 for sperm counts. Treatment with PTU from 6 to 12 wk of age resulted in a 96% increase in mean testis weight at 28 wk of age (treated 39.3 +/- 4.1 g per testis vs. control 20.0 +/- 1.6 g per testis). These testes exhibited normal morphology and increased relative sperm production. Treatment with PTU from either 8 to 14 or 10 to 16 wk of age resulted in approximately a 35% increase in testis mass at 28 wk of age relative to the control value (27.2 +/- 2.0 g and 27.7 +/- 3.6 g vs. 20.0 +/- 1.6 g per testis, respectively). However, both of these groups clearly demonstrated precocious puberty and abnormal spermatogenesis. These results suggest that appropriately timed PTU treatment may result in permanent increases in testis size and sperm production in the domestic fowl.

Effect of methimazole with or without exogenous L-thyroxine on serum concentrations of thyrotropin (TSH) receptor antibodies in patients with Graves' disease

Medical treatment of Graves' disease involves use of antithyroid drugs with or without the addition of exogenous L-T4. There have been conflicting reports as to whether the addition of T4 reduces TSH receptor antibodies and improves remission rates more than antithyroid drugs alone. To further examine the effect of drug therapy on serum concentrations of TSH receptor antibodies. 70 patients with Graves' disease were treated with methimazole (Tapazole) alone until they were euthyroid. Then they were randomized to receive either: 1) methimazole alone in a dose sufficient to normalize TSH (0.3-5.4 mIU/L; Group 1); 2) 30 mg methimazole daily plus sufficient T4 (Synthroid) to maintain TSH in the high-normal range (2.0-5.4 mIU/L; Group 2); or 3) 30 mg methimazole daily plus sufficient T4 to suppress TSH to below 0.6 mIU/L (Group 3). The duration of treatment in all groups was 18 months. At baseline and after 6 and 18 months, TSH receptor antibodies were measured both by the ability of patients' sera to stimulate cAMP production by FRTL-5 cells (thyroid-stimulating Ig) and by the ability of patients' sera to inhibit binding of radiolabeled TSH to solubilized porcine thyroid membranes (TSH-binding, inhibiting Ig). Thyroid-stimulating Ig(TSI) and TSH-binding, inhibiting Ig(TBII) concentrations were similar among the three groups at baseline. Mean baseline TSI (expressed as the percent of normal control) for all patients combined was 306 +/- 21%. Mean baseline TBII (expressed as percent inhibition of TSH binding) was 38 +/- 2%. TSI was elevated in 85% and TBII was elevated in 75% of patients at baseline. After 18 months, TSI was elevated in 64% of patients, and TBII was elevated in 28%. Serum TSI decreased by 36 +/- 5% during the study, and there was no significant difference in the degree of reduction among the three groups (P = 0.99). Serum TBII decreased by 59 +/- 3%, and there also was no significant difference among the groups (P = 0.83). At baseline, serum TBII correlated with free T4 (r = 0.33, P < 0.01), total T3 (r = 0.55, P < 0.01), and thyroid size (r = 0.35, P < 0.01). There was no correlation between TSI and any of the baseline parameters or between TSI and TBII at any timepoint. In conclusion, we found that the addition of T4 to methimazole does not result in a greater decrease in TSH receptor antibody concentrations than treatment with methimazole alone. From these results, we would predict no difference in remission rates among these patients, but confirmation of this prediction will need to await long-term follow-up of these subjects.

Inhibitory effects of (+/-)-tetrahydropalmatine on thyrotropin-stimulating hormone concentration in hyperthyroid rats

The effects of (+/-)-tetrahydropalmatine ((+/-)-THP) on the hypothalamus-pituitary-thyroid system in rats were investigated. Thyroid function experiments indicated that (+/-)-THP produces significant decreases in thyroid function in hyperthyroid rats after 14 days of treatment. These effects were the same as those of propylthiouracil. However, propylthiouracil also decreased thyroid function in normal rats. Measurements of thyrotropin-stimulating hormone (TSH) demonstrated that (+/-)-THP decreased TSH in hyperthyroid rats after 14 days of treatment; however, propylthiouracil increased TSH in hyperthyroid rats. (+/-)-THP had no influence on TSH, or thyroid and pituitary weight in normal and hyperthyroid rats. We conclude that (+/-)-THP has an antithyroid function and the mechanism of action may be related to the inhibition of TSH in the pituitary.

Fuel utilization by early newborn brain is preserved under congenital hypothyroidism in the rat

Mental retardation associated with hypothyroidism may be caused by impairment of brain ketone body-metabolizing enzymes during the suckling period. However, much evidence suggests that, immediately after delivery, lactate, instead of ketone bodies or glucose, may be the best substrate for the brain. In this work, we have studied the effect of experimentally induced congenital hypothyroidism on the rate of lactate, glucose, and 3-hydroxybutyrate utilization in early neonatal brain slices. Methimazole (MMI) administration to the mothers caused a 5.4- and 1.7-fold decrease in neonatal plasma concentrations of L-thyroxine (T4) and 3,5,3'-triiodo-L-thyronine (T3), respectively. Propylthiouracil (PTU) administration to the mothers caused a 7.3- and > 2-fold decrease in plasma T4 and T3 concentrations, respectively. MMI-induced hypothyroidism did not significantly modify the rate of lactate, glucose, or 3-hydroxybutyrate oxidation to CO2 and their incorporation into lipids by the neonatal brain. However, PTU-induced hypothyroidism decreased the rate of lactate and glucose oxidation to CO2 and their incorporation into lipids by 17% (p < 0.05). 3-Hydroxybutyrate utilization was not modified by this treatment. Separation by HPLC of the lipids revealed that PTU-mediated inhibition of lipid synthesis from lactate and glucose may be accounted for by specific inhibition of the rate of sterol synthesis (15%, p < 0.05), whereas the rate of phospholipid synthesis was unaffected. These results suggest that the early newborn may develop mechanisms aimed at avoiding the possible brain damage caused by the inhibition of lipid synthesis brought about by mild neonatal hypothyroidism.

Dietary goitrogen-induced changes in the transport of 2-deoxy-D-glucose and amino acids across the rat blood-brain barrier

The hypothesis that a defect in the rate-limiting blood-brain barrier (BBB) nutrient transport may be one of the factors responsible for the brain defects seen in some iodine deficiency disorders was tested in Wistar/NIN rats fed potassium thiocyanate (KSCN), a synthetic goitrogen. The BBB nutrient transport was measured by the brain uptake index (BUI) method. Feeding KSCN to female rats (from weaning) through their growth, pregnancy and lactation (G1) but not from conception (G2) or parturition (G3) resulted in a significant decrease (approximately 23%) in the BBB transport of 2-deoxy-D-glucose (2-DG) in their offspring at weaning, compared with controls (C). Post-weaning KSCN-feeding (G4) of control pups did not affect their BBB 2-DG transport (BUI: 36.2 +/- 4.98, vs 38.8 +/- 4.11). The effects of different KSCN regimens on BBB transport of leucine (leu), tyrosine (tyr) and sucrose (background marker) were inconsistent, of smaller magnitude (approximately 10%) and appeared to be of little significance. Withdrawing KSCN from the diet of chronically KSCN-fed (G1) mothers from conception (G5) or parturition (G6) prevented the impairment of BBB 2-DG transport in pups (BUI: 27.0 +/- 4.98, 20.8 +/- 3.27, 26.9 +/- 3.99 and 28.3 +/- 3.47 in C, G1, G5 and G6 pups, respectively); this was reversed by feeding the control diet to G1 pups from weaning. Withdrawal of dietary KSCN did not affect BBB transport of leu, tyr and sucrose. The decreased BBB transport of 2-DG in G1 pups appears to be due to a decrease in affinity (Kt app 5.46 vs 4.15 mM) rather than in the capacity (Tmax app 0.94 vs 0.91 mumoles/g/min) of the transport system. Intracarotid injections of KSCN per se had no effect on BBB 2-DG transport, suggesting that the effects may be secondary to the altered thyroid status of the animal.

Inhibition of 5'DI and 5'DII L-tiroxine (T4) monodeiodinases. Effect on the hypothalamo-pituitary ovarian axis in adult hypothyroid rats treated with T4

Hypothyroid female rats were treated with T4 and their 5'DI and 5'DII deiodinases were inhibited by PTU and IOP administration to determine whether the effect of T3 on reproductive function is a primary event at hypothalamo-pituitary levels or ovarian levels. Hypothyroid adult female rats were divided into four groups: Hypothyroid without treatment (H); hypothyroid treated with T4 (H-T4); hypothyroid treated with T4 plus propylthiouracil (H-T4-PTU), and hypothyroid treated with T4 plus iopanoic acid (H-T4-IOP). A group of euthyroid rats (E) was included as control. Estrous cycle, ovarian histological changes and serum estradiol and gonadotropin levels (basal and after GnRH) were searched in all groups. In view of our results and since sexual cycles and puberal pattern in gonadotropin secretion were restored after all treatments we can suggest: That T4 could have an intrinsic effect on reproductive function in adult hypothyroid female rats or that another compensatory T3 mechanism unaffected by IOP could exist. The present report points out that the effect of T3 on reproductive function could be a primary event at hypothalamopituitary levels although an effect at ovarian levels could not be excluded.

Blockade of the estrogen induced increase in progesterone receptor caused by propylthiouracil, an anti-thyroid drug, in a transplantable pituitary tumor in rats

It is well known that estrogen (E2) induces progesterone receptor (PR) in the uterus and the mammary gland. In MtT/F84, a pituitary tumor, which was established in our laboratory and has been maintained with in vivo passages, we investigated the PR regulation by E2 in relation to the host's thyroidal status. The PR level in the tumor had increased five fold 48 h after an E2 injection. When the host rats were treated with propylthiouracil (PTU), an anti-thyroid drug, the induction of PR after an E2 injection was completely blocked. This result is consistent with our previous findings indicating that E2 responsiveness in the tumor may be under the control of thyroid hormones. The estrogen receptor (ER) level in the tumor treated with PTU was 15% of the control. This low ER level may account for the blocking of PR induction after an E2 injection. When the host animals were continuously treated with various doses of E2, the PR level in the tumor rose in correlation with the E2 doses. PTU administration, however, did not prevent long term induction of PR by continuous E2 treatment. Our findings suggest that PTU lower the ER level and suppresses the short term estrogenic actions such as PR induction after an E2 injection.

Effects of thyroid hormone on the androgenic expression of KAP gene in mouse kidney

The kidney androgen-regulated protein (KAP) gene exhibits a cell-specific hormonal regulation of its expression in the epithelial cells of proximal tubules of mouse kidney, where T3 is required for constitutive expression in the straight segments and androgens for expression in the convoluted ones. By using different models of hypothyroidism, we demonstrate that maximal androgen-mediated induction of the gene depends on thyroid hormone as well. This constitutes a specific event, since vitamin D3 cannot mimic the effects of T3, albeit their remarkable functional relationship. It is also shown that while congenital hypothyroid hyt/hyt male mice, exposed to maternal T3 in the gestational period, exhibit diminished but existent androgen-dependent cortical responses, mice exposed to goitrogens during gestation and postnatally are unable to express the gene even at postnatal day ninety. Impairment of KAP cortical expression in hypothyroid animals does not correlate with lower levels of androgens or androgen receptor expression.

Propylthiouracil treatment reduces long-term potentiation in area CA1 of neonatal rat hippocampus

Rat pups were made hypothyroid by exposure to propylthiouracil in drinking water beginning at 1 week of age, and the degree of long-term potentiation (LTP) in hippocampal area CA1 determined from brain slices of animals ranging in age from 2 to 6 weeks. Serum T3 levels were less than 20% of that of age matched controls after 3 weeks of treatment, and remained at that level. Relative to the age-matched controls, LTP was reduced significantly after 2 weeks of treatment. These observations are consistent with the conclusion that LTP magnitude is a reflection of cognitive function, which is known to be depressed in hypothyroid conditions in both animals and man.

Cardiac alpha-adrenergic receptor expression is regulated by thyroid hormone during a critical developmental period

Although thyroid hormone is obligatory for the development of cardiac beta-adrenergic receptors, it is difficult to assign a specific role for the hormone in receptor ontogeny because beta-receptor expression is affected similarly in the adult. We have determined whether thyroid hormone plays a role in receptor development by evaluating alpha 1-adrenergic receptors, which in the adult are downregulated by thyroid hormone. Propylthiouracil given from gestational day 17 through postnatal day 5 caused significant deficits in the number of alpha 1-receptors and values resolved to normal in parallel with hormone level recovery. When propylthiouracil was administered later (postnatal days 11 through 15) only a transient deficit in alpha 1-receptor binding was seen; hyperthyroidism (triiodothyronine) could still evoke stimulation of receptor expression at this stage. The effects on receptor expression were distinguished from general effects on cell differentiation by examining alpha 2-receptors, which disappear over the first three postnatal weeks; delayed differentiation caused by propylthiouracil would slow the decline in alpha 2-receptors, whereas accelerated differentiation caused by triiodothyronine would hasten the decline. Instead, the effects were similar to those on alpha 1-receptors: perinatal propylthiouracil administration reduced, and neonatal triiodothyronine administration enhanced, alpha 2-receptor binding sites. Thus, thyroid hormone plays a role in the control of cardiac adrenergic receptor expression during a critical development period, with conjoint regulation of the multiple receptor subtypes present within the tissue. As adrenergic stimulation is important in maintaining cardiac function in the perinatal period, alterations of thyroid status during this period can be expected to result in abnormal reactivity and increased perinatal risk.

Methimazole has no dose-related effect on the serum concentrations of soluble class I major histocompatibility complex antigens, soluble interleukin-2 receptor, and beta 2-microglobulin in patients with Graves' disease

Soluble class I major histocompatibility antigens (sHLA), beta 2-microglobulin (beta 2-M), and soluble interleukin-2 receptor (sIL-2R), are secreted by B and T lymphocytes upon activation, and have been used as markers of immune activation in several diseases. Thirty-two Graves' disease patients were randomly assigned to three methimazole (MMI) regimens of treatment: (1) low-dose, starting with 45 mg/day, and lowering the dose thereafter to maintain normal serum thyroid hormones; (2) MMI 60 mg/day + levothyroxine, and (3) MMI 30 mg/day + levothyroxine. Serum sHLA, beta 2-M, sIL-2R, TSH receptor antibodies (TSH-R Ab), T3, and free T4 (fT4) were measured at diagnosis and at weeks 4, 12, and 24 (end of treatment). Patients were followed-up after treatment for at least 24 weeks (24 to 89). At diagnosis, serum levels of sIL-2R, beta 2-M, sHLA, and TSH-R Ab were elevated. Serum sIL-2R, beta 2-M, sHLA, and TSH-R Ab decreased with treatment. No effect of the varying MMI regimens on these parameters was observed. Soluble IL-2R correlated positively with T3, fT4, beta 2-M, sHLA, and TSH-R Ab. Statistically significant, but weak, correlations (r < 0.35) were observed between beta 2-M, sHLA, and TSH-R Ab, between beta 2-M, T3, and fT4, and between TSH-R Ab and T3. Recurrence rates were not associated either with the MMI regimen or any of the parameters studied, with the exception of elevated initial TSH-R Ab levels. Serum sHLA, beta 2-M, and sIL-2R are increased in untreated Graves' disease, and decrease during treatment. No MMI dose-related differences were observed in these parameters, and in the recurrence rate. Unfortunately, sHLA, beta 2-M, and sIL-2R were not useful predictors of prolonged remission after MMI treatment.

Comparison of Kodak Amerlite FT4 and TSH-30 with T4 and TSH as first-line thyroid function tests

OBJECTIVES

To evaluate the effect of test automation and a change in strategy for thyroid function tests (TFT) on personnel needs and turn-around time. The first-line TFT were changed from T4 and TSH to FT4 and TSH-30.

DESIGN AND METHODS

Samples received for TFT from 357 randomly selected patients were analyzed by RIA for T4, and by IRMA for TSH as first-line tests. FT3 and TBG were requested as back-up tests when indicated. Patients were classified on the basis of these results and the clinical information received. All the samples were reanalyzed for FT4 and TSH on the Amerlite Processing Center, which is a batch, semiautomated immunoassay system. The thyroid status of the patients was compared using the two protocols and available clinical data.

RESULTS

There was good correlation between TSH-IRMA and TSH-30 in the 160 patients classified as euthyroid (r = 0.956; p < 0.001) and no euthyroid patient was reclassified with the new strategy. In 21 patients with borderline raised TSH-IRMA, FT4 was found to be low in only 2. All 11 patients classified as hypothyroid had TSH results greater than 10 mU/L and all except 2 patients had FT4 less than 11 nmol/L. The status of 21 hyperthyroid as well as 40 patients on carbimazole could be determined biochemically on the basis of agreement between both the FT4 and TSH-30 results. FT3 was only required if the FT4 and TSH-30 results were not in agreement. In 42 patients on T4 therapy, adequacy of replacement was assessed better using FT4 and TSH-30. No patient required backup testing with TBG to determine thyroid status using the new testing protocol. The change in TFT protocol reduced the 95% turn-around time from 3 days to 1 day.

CONCLUSION

The introduction of FT4 and TSH-30 as first-line TFT improved the turn-around time for TFT, resulted in 25% reduction in personnel requirements, 60% reduction in FT3 assays, and discontinuation of TBG assay.

Effects of hyperthyroidism on expression of a phosphoenolpyruvate carboxykinase/bovine growth hormone gene in transgenic mice

Thyroid hormone (T3) responsiveness of the PEPCK promoter in vivo was examined in both PEPCK/bGH(460) and PEPCK/bGH(335) mouse lines. Transgenic and non-transgenic littermates were treated with methimazole or PTU for 6 or 4 weeks, respectively, then treated +/- T3 for 10 days. In PEPCK/bGH(460) and PEPCK/bGH(355) transgenic mice, the bGH mRNA was decreased by 65% and 46%, respectively, in hyperthyroid mice when compared to euthyroid controls. Endogenous PEPCK mRNA was decreased by 33% in hyperthyroid non-transgenic mice. The conclusion of this study is that chronic hyperthyroidism in mice inhibits PEPCK-directed expression of the transgene when either the -460/+73 or the -355/+73 promoter/regulatory elements are used.

[The electrophoretic mobility of the erythrocytes in rats during body adaptation to low-temperature exposure]

The action of a low temperature (-4 degrees C) on electrophoretic mobility of rat blood erythrocytes (EME) was studied. The stress provoked by the low temperature renders a considerable influence on EM of erythrocytes, but the degree and disposition of arising changes depend on the duration of temperature coercion. Two weeks after conducting cooling seances (beginning with 15 min, with an every day increase in exposition by 10 min), the response reaction was manifested in the rise of asymmetry and excess of distribution curve of EME index. The prolongation of cold adaptation to 6 weeks was accompanied with the authentic lowering of the mean mobility of cells, in addition to a subsequent sharp modification of erythrogram profile. The cooling of animals conducted against the background of thyreoidine has given, as a whole, similar results, although the use of the protector alleviated the consequences of low temperature coercion.

Atom level electrotopological state indexes in QSAR: designing and testing antithyroid agents

PURPOSE

To design antithyroid agents with less side effects, the electrotopological-state (E-state) indexes of thiourylene moiety (SN&S) was utilized as a guideline to develop five acrylic thiourylene-type compounds with reduced antioxidant property.

METHODS

These agents were synthesized and screened for antithyroid activity in rats using 125I-thiocyanate discharge technique. In addition, chemiluminescence studies on the activated polymorphonuclear leukocytes (PMNLs) were also conducted to reveal antioxidant properties of the tested compounds.

RESULTS

A linear relationship between the in vitro literature value of the formation constants of thiourylene-type compounds with iodine (Kc) and the SN&S was observed and utilized in designing those agents. At least one of the compounds (abouthiouzine) was found to have a potential value as an antithyroid agent. The relative efficacy of abouthiouzine [1-n-butyl-3(isonicotinamido)-2-thiourea], after equimolar dose, was 102% and 51.5% of that of propylthiouracil with respect to the rate of 125I-discharge and 125I-uptake, respectively. In addition, chemiluminescence studies on PMNLs revealed that abouthiouzine has slight oxidant property. Such properties may provide advantages in avoiding the iatrogenic hypothyroidism and antithyroid-induced immunological reactions.

CONCLUSIONS

The E-state approach provides guidelines to economize efforts and cost of designing new antithyroid drugs.

Iodide-dependent regulation of thyroid follicular cell proliferation: a mediating role of autocrine insulin-like growth factor-I

An inhibitory action of intracellular iodide on the autocrine production of insulin-like growth factor-I (IGF-I) by thyroid follicular cells (TFCs) in vitro has been investigated as a possible mechanism underlying the iodide-dependent control of TFC proliferation. IGF-I release from primary monolayer cultures of porcine TFCs increased 5-fold between 24 and 168 h of incubation. Confirmation of a mediating role of IGF-I in TFC proliferation was obtained by exposing TFCs to an immunoadsorbing IGF-I antiserum, which led to a significant (P < 0.05) decline in [methyl-3H]thymidine incorporation, relative to TFCs exposed to preimmune serum. Exposure of TFCs to sodium iodide (NaI; 0.1-100 mumol/l) led to an attenuation of the IGF-I content of the cell-conditioned medium. This was accompanied by a reduction in [methyl-3H]thymidine incorporation that was affected by IGF-I immunoneutralization. The inhibitory effect of NaI on IGF-I production and [methyl-3H]thymidine incorporation were reversed by the thionamide compound methimazole (MMI; 1 mmol/l), exposure to which also led to significant (P < 0.001) increases above control values. However, a residual suppressive effect of NaI on [methyl-3H]thymidine incorporation suggested that certain of the TFC growth-attenuating effects of iodide may not be dependent upon organification. While providing evidence, therefore, for a direct relationship between iodide exposure, suppression of autocrine IGF-I production and a regulation of TFC proliferation, the present studies also suggest that suppression of TFC proliferation by iodide may be partially mediated by MMI-insensitive events.

[The effect of carbimazole on lactate dehydrogenase isoenzymes and thyroid hormone levels in sheep]

The oxidative processes in the organism are activated by hormones of the thyroid gland. The pyruvate-lactate component catalyzed by lactate dehydrogenase presents one of the important oxidic-reductive systems in the animal organism of biochemical importance (EC. 1.1.1.27). In certain cases of the thyroid gland disturbances antithyroid drugs, such as derivatives of thiouracil, mercaptoimidazole and some others may be used for the treatment of men and animals (Marchant et al., 1979; Negwer, 1987). In the present study, the activity changes of lactate dehydrogenase isoenzymes in the blood plasma of young rams and ewe hoggets in experiments with carbimasole [carbimasolum(1-carbaethoxy-3-methyl-2-thioimidazolum) ] have been studied. The dose of carbimasole at the time of sampling (May, 1993) was 7O mg per animals and day. In May, no significant differences in T3 and T4 concentrations in the serum of experimental and control animals in males and females were found (Tab. 1). The T3 concentrations in the experimental group of young rams were 0.56 +/- 0.21 nmol/l (n = 3), in ewe hoggets 0.70 +/- 0.19 nmol/l (n = 6). The T4 concentrations in young rams were 39.15 +/- 24.15 nmol/l (n = 3), in ewe hoggets 48.6 +/- 15.3 nmol/l (n = 6). Out of lactate dehydrogenase isoenzymes, only LD4 exhibited significant differences (P < 0.02) in the blood plasma of ewe hoggets (Tab. I). In the course of these months, no clinical signs of hypothyrosis were observed in experimental animals.

Role of goitrogens in iodine deficiency disorders & brain development

Although iodine deficiency has primarily been implicated in the causation of goitre, the significant role played by food goitrogens in the etiology of iodine deficiency disorder (IDD) is being increasingly recognized. Impaired brain development is the major cause of concern in IDD. Detailed experimental studies were undertaken to ascertain various biochemical changes associated with developing brain in response to treatment with a goitrogens--thiocyanate. Addition of thiocyanate to food deprived of KI brought down significantly the circulating levels of thyroxine (T4) in rats. Nucleic acids and protein content in different regions of brain were significantly lowered in rat pups exposed to thiocyanate. The rate of microtubule assembly, which is detrimental for neurite growth was considerably lowered, thereby influencing both myelin deposition and synaptogenesis in developing brain. Goitrogen intake not only caused an adaptive increase in the activity of type II 5'-deiodinase, which governs availability of triiodothyronine (T3) in brain, it also increased the latter's binding to brain nuclear receptors under conditions of thiocyanate induced hypothyroid state. Addition of adequate quantities of KI mitigated thiocyanate induced alterations by restoring circulating level of thyroxine. These investigations suggest that goitrogens play a significant role in influencing biochemical events unique to developing brain.

Effect of thyroid state on cardiac electrical activity of the frog Rana esculenta

The effects of altered thyroid states on the heart rate and ventricular electrophysiological properties of the frog were examined. Hypothyroidism was induced by a 10-day treatment with propylthiouracil and produced decreased serum-free and total triiodothyronine levels below detectable concentrations. Hyperthyroidism, elicited by a 5-day treatment with triiodothyronine, was associated with increased serum thyroid hormone levels. The hypothyroid state was associated with a significantly decreased heart rate measured in vivo and an increased duration of the action potential recorded in vitro from ventricular fibers. Hyperthyroidism was associated with an increased heart rate and a decreased ventricular action potential duration (APD). The dependence of APD on temperature was affected by thyroid status. An increase from 25 to 30 degrees barely shortened the repolarization phase in hyperthyroids, minimally (13.3%) shortened that in euthyroids, and greatly (43.7%) shortened that in hypothyroids; the APD was similar in euthyroid and hypothyroid frogs. The shortening of the repolarization phase, by increased stimulation frequency, was also greater for hypothyroid frogs. In this case, however, the differences in APD among groups remained significant at all the frequencies tested.