No abstract

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 , IL-6 and TNF 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 stimulated D1 and D2 dosedependently and D2 activity was increased by TNF . When GH3 cells were cocultured with TtT/Gf cells, D2 activities were 2·3-fold lower than in GH3 cells cultured alone. TNF (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 , TNF 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 and TNF activate the transcription factor NF 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.

Objective: Local 5 0 -deiodination of L-thyroxine (T 4 ) to active thyroid hormone 3,3 0 ,5-tri-iodothyronine (T 3 ) catalyzed by the two 5 0 -deiodinase enzymes (D1 and D2) regulates various T 3 -dependent functions in the anterior pituitary and has been well studied in rodents. Only limited information about deiodinase expression and its cellular distribution in human anterior pituitaries is available. Design: We examined 5 0 -deiodinase enzyme activities in pituitary adenomas (18 non-functioning, seven TSH-producing, one GH-and TSH-producing, five GH-producing, eight prolactin (PRL)-producing, two adenomas each from patients with Cushing's disease and Nelson's syndrome) and three normal anterior pituitaries. Methods: Activities were measured as release of 125 I 2 from tyrosyl-ring labeled reverse T 3 with or without propylthiouracil, a potent inhibitor of D1 which does not influence D2 activities. Results: Most of the adenomas and normal tissues expressed both isoenzymes, with D2 activity higher than D1. In a few tissues D1 activity was higher than D2 and some tissues did not express D1 activity at all. Highest activities of both enzymes were found in TSH-and PRL-producing adenomas but absolute activities and the D1/D2 ratio were variable in the same kind of tumor in different patients. Conclusion:The finding that all examined tissues expressed 5 0 -deiodinase activity, most of them expressing both isoenzymes, implies that both enzymes are still active in tumors and that local deiodination is important for the function and feedback regulation of human anterior pituitary.

Objective: Proinflammatory cytokines are involved in the pathogenesis of non-thyroidal illness (NTI), as shown by studies with IL-6 2/2 and IL-12 2/2 mice. Interleukin (IL)-6 changes peripheral thyroid hormone metabolism, and IL-12 seems to be involved in the regulation of the central part of the hypothalamic-pituitary-thyroid (HPT) axis during illness. IL-18 is a proinflammatory cytokine which shares important biological properties with IL-12, such as interferon (IFN)-g-inducing activity. Design: By studying the changes in the HPT-axis during bacterial lipopolysaccharide (LPS)-induced illness in IL-18 2/2 , IFNgR 2/2 and wild-type (WT) mice, we wanted to unravel the putative role of IL-18 and IFNg in the pathogenesis of NTI. Results: LPS induced a decrease in pituitary type 1 deiodinase (D1) activity (P , 0.05, ANOVA) in WT mice, but not in IL-18 2/2 mice, while the decrease in D2 activity was similar in both strains. LPS decreased serum thyroid hormone levels and liver D1 mRNA within 24 h similarly in IL-18 2/2 , and WT mice. The expression of IL-1, IL-6 and IFNg mRNA expression was significantly lower in IL-18 2/2 mice than in WT, while IL-12 mRNA expression was similar. IFNgR 2/2 mice had higher basal D1 activity in the pituitary than WT mice (P , 0.05); LPS induced a decrease of D2, but not of D1, activity in the pituitary which was similar in both strains. In the liver, the LPS-induced increase in cytokine expression was not different between IFNgR 2/2 mice and WT mice, and the decrease in serum T 3 and T 4 levels and hepatic D1 mRNA was also similar. Conclusions: The relative decrease in serum T 3 and T 4 and liver D1 mRNA in response to LPS is similar in IL-18 2/2 , IFNgR 2/2 and WT mice despite significant changes in hepatic cytokine induction. However, the LPS-induced decrease in D1 activity in the pituitary of WT mice is absent in IL-18 2/2 mice; in contrast, LPS did not decrease pituitary D1 activity in the IFNgR 2/2 mice or their WT, which might be due to the genetic background of the mice. Our results suggest that IL-18 is also involved in the regulation of the central part of the HPT axis during illness.

Local deiodination of L-thyroxine (T4) to the active thyroid hormone T3 via two 5'deiodinase isoenzymes (5'DI and 5'DII) plays an important role for various T3-dependent functions of the anterior pituitary (AP). Recently, it was reported that 3,5-T2, the 5'deiodination product of T3, acts as a specific agonist in the feedback mechanism on TSH secretion at the pituitary level. We now examined the effects of 3,5-T2 on pituitary 5'deiodinase activities in vivo in male, adult rats and in vitro using rat AP reaggregate cultures and the somatomammotroph cell line GH3. 5'DI activity in the AP was transiently increased after a single injection of 3,5-T2. Serum TSH levels declined, and 24 h after 3,5-T2 application, betaTSH steady-state mRNA levels in the APs were markedly lower. In reaggregate cultures of the AP, 3,5-T2 stimulated 5'DI activity 24 h after application, dose-dependently. Compared with 5'DI activities, those of 5'DII were an order of magnitude lower, in vivo as well as in vitro, and were rapidly and transiently decreased by the higher dose of 3,5-T2. GH3 cells responded to 3,5-T2 and T3 by an 1.7-fold stimulation of 5'DI activity. Stimulation of DNA-binding was demonstrated in electrophoretic mobility shift assays for a specific RXR-containing protein complex with a DR+4 thyroid hormone response element of the human type 1 5'DI promoter using nuclear extracts from GH3 cells treated with 3,5-T2. In summary, 3,5-T2 and T3 exert direct thyromimetic effects on 5'DI activity and TSHbeta expression at the pituitary level. 5'DI is regulated by its substrate(s) and/or products and may serve an important function within the modulation of thyroid hormone-dependent gene expression in the AP.