Search Results

You are looking at 21 - 30 of 199 items for :

Clear All
Free access

Alessandro Marsili, Edith Sanchez, Praful Singru, John W Harney, Ann Marie Zavacki, Ronald M Lechan and P R Larsen

T 4 to T 3 by the type 2 deiodinase (D2) is required for suppression of TSH at the pituitary level ( Larsen et al . 1979 ). The requisite degree of saturation of the thyrotroph nuclear T 3 receptors requires both circulating T 3 and D2-mediated

Free access

A Boelen, J Kwakkel, X G Vos, W M Wiersinga and E Fliers

Introduction During fasting, profound changes occur in the hypothalamic part of the hypothalamic–pituitary–thyroid axis (HPT axis), i.e. increased type 2 deiodinase (D2) activity in the arcuate nucleus (ARC) ( Diano et al. 1998

Free access

B Anguiano, R Rojas-Huidobro, G Delgado and C Aceves

reported that the lactating rat mammary gland exhibits type 1 deiodinase (Dio1) which catalyzes the T4 to T3 conversion. This enzyme can be detected beginning in mid-pregnancy, and its synthesis increases considerably 48 h postpartum. In mid

Free access

CH Verhoelst, S Van Der Geyten and VM Darras

Iodothyronine deiodinase in vitro activity studies in the chicken showed the presence of type I and type III iodothyronine deiodinase activity in both liver and kidney. Due to the lack of a specific antiserum the cellular localization of the deiodinase proteins could not be revealed until now. In the present study, specific antisera were used to study the renal and hepatic distribution of type I and type III iodothyronine deiodinase protein in the chicken. Immunocytochemical staining of liver tissue led to an immunopositive signal in the hepatocytes in general. Moreover, a zonal distribution could be detected for both enzymes. Maximum protein expression was shown in a thin layer of hepatocytes bordering the blood veins. Although pericentral localization of type I deiodinase protein has been previously reported in the rat, no data were given concerning type III deiodinase protein. In the present study, we report the co-localization of both enzymes in the chicken. Co-expression of the deiodinases was also found in the kidney. Expression of both proteins was associated with the tubular epithelial cells and with the transitional epithelium, and the inner longitudinal and outer circular muscle layers of the ureter. No staining could be detected in the lamina propria or in the fat tissue surrounding the ureter.

Free access

TG Frankenfeld, VM Correa Da Costa, CC Nascimento-Saba, TM Ortiga-Carvalho, RM Santos, PC Lisboa, DP Carvalho and D Rosenthal

Some authors have reported increased serum thyrotrophin (TSH) in animals chronically treated with lithium, suggesting that lithium might decrease pituitary thyroxine (T(4))-5'-deiodinase activity. On the other hand, the effect of lithium treatment on thyroidal T(4)-5'-deiodinase activity is also unknown. The present study was undertaken to evaluate the effects of lithium treatment on pituitary and thyroid T(4)-5'-deiodinase activity. Serum and pituitary TSH levels and thyroidal and pituitary T(4)-5'-deiodinase activities were determined in 3-month-old isogenic male Dutch-Miranda rats treated with lithium for 8 weeks. Chronic lithium treatment produced a slight increase in pituitary TSH content, but no change in serum TSH, and a significant increase in the thyroidal T(4)-5'-deiodinase activity. However, the pituitary T(4)-5'-deiodinase activity was unaffected by lithium administration. As far as we know, the present data show for the first time that chronic lithium treatment can increase the thyroxine to tri-iodothyronine conversion in the murine thyroid gland, be it directly or indirectly.

Free access

JC Solis-S, P Villalobos, A Orozco and C Valverde-R

The initial characterization of a thyroid iodotyrosine dehalogenase (tDh), which deiodinates mono-iodotyrosine and di-iodotyrosine, was made almost 50 years ago, but little is known about its catalytic and kinetic properties. A distinct group of dehalogenases, the so-called iodothyronine deiodinases (IDs), that specifically remove iodine atoms from iodothyronines were subsequently discovered and have been extensively characterized. Iodothyronine deiodinase type 1 (ID1) is highly expressed in the rat thyroid gland, but the co-expression in this tissue of the two different dehalogenating enzymes has not yet been clearly defined. This work compares and contrasts the kinetic properties of tDh and ID1 in the rat thyroid gland. Differential affinities for substrates, cofactors and inhibitors distinguish the two activities, and a reaction mechanism for tDh is proposed. The results reported here support the view that the rat thyroid gland has a distinctive set of dehalogenases specialized in iodine metabolism.

Free access

J Kwakkel, W M Wiersinga and A Boelen

characteristic decrease of liver 5′-deiodinase type 1 (D1) mRNA expression and activity during illness, which contributes to the diminished serum T3 levels. ( Boelen et al. 1995 , 1996 , Wiersinga 2005 , Jakobs et al. 2002 ). D1 mRNA expression in

Free access

A Baur, K Bauer, H Jarry and J Kohrle

Cytokines are locally produced in the anterior pituitary and act through para-/autocrine mechanisms to modulate cell growth and hormone production. 5'-Deiodinases type I (D1) and type II (D2) are also expressed in the anterior pituitary and play an integrative role in the regulation of hormone production and pituitary feedback. D1 activity is known to be regulated by proinflammatory cytokines in liver and thyroid. Therefore, we examined the effects of IL-1 beta, IL-6 and TNF alpha on 5'-deiodinase activities in reaggregates of rat anterior pituitaries and rat somatomammotroph GH3 cells cultured alone, or in a bicameral culture system together with the murine folliculo-stellate (FS) cell line TtT/Gf. In reaggregate cultures of rat anterior pituitaries IL-1 beta stimulated D1 and D2 dose-dependently and D2 activity was increased by TNF alpha. When GH3 cells were cocultured with TtT/Gf cells, D2 activities were 2.3-fold lower than in GH3 cells cultured alone. TNF alpha (50 ng/ml) and IL-6 (100 U/ml) stimulated D2 in GH3 cells when the cells were cultured alone and treated with these cytokines for 24 h. When TtT/Gf cells in the coculture model were treated with IL-1 beta, TNF alpha and IL-6, no effect on D1 or D2 activities in GH3 cells was observed. In male, adult rats a single LPS injection (i.p.) stimulated D2 and D1 activities in the anterior pituitary, and decreased liver D1 activities and serum TSH levels. In vitro, LPS stimulation of the coculture model of GH3 and FS cells also increased D1 activity. Electrophoretic mobility shift assays (EMSAs) revealed that IL-1 beta and TNF alpha activate the transcription factor NF kappa B in reaggregates of rat anterior pituitaries and in TtT/Gf cells cultured alone or cocultured with GH3 cells. Taken together, these findings imply that in anterior pituitary cells 5'-deiodinase activities are stimulated by locally produced cytokines in a para-/autocrine manner but cell types other than FS cells seem to mediate some of the effects.

Free access

SM van der Heide, BJ Joosten, ME Everts and PH Klaren

We have investigated the hypothesis that uridine 5'-diphosphate (UDP)-glucuronyltransferases (UGTs) and beta-glucuronidase are jointly involved in a mechanism for the storage and mobilization of iodothyronine metabolites in liver, kidney, heart and brain. Specifically, we predicted UGT activities to decrease and increase respectively, and beta-glucuronidase activity to increase and decrease respectively in hypo- and hyperthyroidism. To this end we have studied the effects of thyroid status on the activities of different enzymes involved in thyroid hormone metabolism in liver, kidney, heart and brain from adult rats with experimentally induced hypo- and hyperthyroidism. We used whole organ homogenates to determine the specific enzyme activities of phenol- and androsteron-UGT, beta-glucuronidase, as well as iodothyronine deiodinase types I and II. Deiodinase type I activities in liver and kidney were decreased in hypothyroid animals and, in liver only, increased in hyperthyroidism. Deiodinase type II activity was increased in hyperthyroid rat kidney only. Interestingly, in the heart, deiodinase type I-specific activity was increased fourfold, although the increase was not statistically significant. Cardiac deiodinase type I activity was detectable but not sensitive to thyroid status. Hepatic phenol-UGT as well as androsteron-UGT activities were decreased in hypothyroid rats, with specific androsteron-UGT activities two to three orders of magnitude lower than phenol-UGT activities. Both UGT isozymes were well above detection limits in heart, but appeared to be insensitive to thyroid status. In contrast, cardiac beta-glucuronidase activity decreased in hypothyroid tissue, whereas the activity of this enzyme in the other organs investigated did not change significantly.In summary, cardiac beta-glucuronidase, albeit in low levels, and hepatic phenol-UGT activities were responsive only to experimental hypothyroidism. Although a high basal activity of the pleiotropic beta-glucuronidase masking subtle activity changes in response to thyroid status cannot be ruled out, we conclude that hepatic, renal and cardiac UGT and beta-glucuronidase activities are not regulated reciprocally with thyroid status.

Restricted access

F. Tsukahara, T. Muraki and T. Nomoto

ABSTRACT

Serum concentrations of thyroid hormones and the properties of iodothyronine deiodinase in tissues of the house musk shrew, Suncus murinus, were examined and compared with those of the rat. Serum concentrations of thyroxine (T4) and 3,3′,5′-tri-iodothyronine (rT3) were higher, while the serum concentration of 3,5,3′-tri-iodothyronine (T3) was lower in the shrew than in the rat. Among liver, kidney, skeletal muscle, heart, brown adipose tissue (BAT), spleen, lung, testes and thymus homogenates of the shrew, T4 5′-deiodinase (5′D) activity was highest in BAT, and rT3 5′D activity was highest in both the liver and BAT. Intermediate or low T3 5-deiodinase activity was noted in all tissues examined. Activity of 5′D for T4 and rT3 in liver and kidney was much lower, while that of BAT was much higher in the shrew than in the rat. Liver and kidney 5′D may be type-I and that of BAT may be type-II in the shrew, judging from its response to 6-n-propyl-2-thiouracil and iopanoic acid and substrate preference. Thus 5′D of the shrew was similar to that of the rat in type, but was different with respect to its activity in some peripheral tissues. This difference may have relevance to the low T3 state of the shrew.

Journal of Endocrinology (1990) 125, 117–122