Thyroid hormone uptake in cultured rat anterior pituitary cells: effects of energy status and bilirubin

Transport of thyroxine (T(4)) into the liver is inhibited in fasting and by bilirubin, a compound often accumulating in the serum of critically ill patients. We tested the effects of chronic and acute energy deprivation, bilirubin and its precursor biliverdin on the 15-min uptake of [(125)I]tri-iodothyronine ([(125)I]T(3)) and [(125)I]T(4) and on TSH release in rat anterior pituitary cells maintained in primary culture for 3 days. When cells were cultured and incubated in medium without glucose and glutamine to induce chronic energy deprivation, the ATP content was reduced by 45% (P<0. 05) and [(125)I]T(3) uptake by 13% (NS), but TSH release was unaltered. Preincubation (30 min) and incubation (15 min) with 10 microM oligomycin reduced ATP content by 51% (P<0.05) and 53% (P<0. 05) under energy-rich and energy-poor culture conditions respectively; [(125)I]T(3) uptake was reduced by 66% (P<0.05) and 64% (P<0.05). Neither bilirubin nor biliverdin (both 1-200 microM) affected uptake of [(125)I]T(3) or [(125)I]T(4). Bilirubin (1-50 microM) did not alter basal or TRH-induced TSH release. In conclusion, the absence of inhibitory effects of chronic energy deprivation and bilirubin on thyroid hormone uptake by pituitary cells supports the view that the transport is regulated differently than that in the liver

Pre-rehabilitation sense of coherence as a predictor of symptom change after rehabilitation

Sense of coherence (SOC) constitutes the key component of salutogenesis theory. It reflects individuals' confidence that their environment is comprehensible and manageable and that their lives are meaningful. Research demonstrates a strong cross-sectional relationship between SOC and mental health. However, little is known about SOC's temporal stability and its potential to predict changes in psychopathological symptom severity in different settings. The goal of the current study was to address this gap. The sample of the two-wave longitudinal study consists of 294 patients receiving inpatient psychotherapeutic (and psychopharmacological) treatment for various psychological disorders at a German psychosomatic rehabilitation clinic. SOC (Antonovsky, Social Science & Medicine, 1993, 36, 725-733) and outcome measures (i.e., general mental health problems, depression and anxiety symptoms) were assessed within two days of arrival and at the end of rehabilitation (week 5/6). SOC was significantly enhanced after treatment whereas psychopathological symptoms were significantly reduced. Regression analyses revealed that pre-treatment SOC was a significant negative predictor of post-treatment symptom severity for all outcome measures even after controlling for pre-treatment symptoms. The current findings provide first evidence that SOC is a significant unique predictor of symptom change. Future studies need to further investigate longitudinal associations between SOC and mental health outcomes in different settings

Uptake of triiodothyronine and triiodothyroacetic acid in neonatal rat cardiomyocytes: effects of metabolites and analogs

Cellular and nuclear uptake of [125I]tri-iodothyronine (T3) and [125I]triiodothyroacetic acid (Triac) were compared in cardiomyocytes of 2-3 day old rats, and the effect of thyroid hormone analogs on cellular T(3) uptake was measured. Cells (5-10 x 10(5) per well) were cultured in DMEM-M199 with 5% horse serum and 5% FCS. Incubations were performed for from 15 min to 24 h at 37 degrees C in the same medium, 0.5% BSA and [125I]T3 (100 pM), or [125I]Triac (240 pM). Expressed as % dose, T(3) uptake was five times Triac uptake, but expressed as fmol/pM free hormone, Triac uptake was at least 30% (P<0.001) greater than T3 uptake, whereas the relative nuclear binding of the two tracers was comparable. The 15 min uptake of [125I]T3 was competitively inhibited by 10 microM unlabeled T3 (45-52%; P<0.001) or 3,3'- diiodothyronine (T2) (52%; P<0.001), and to a smaller extent by thyroxine (T(4)) (27%; 0.05<P<0.1). In contrast, 10 microM 3,5-T2, Triac, or tetraiodothyroacetic acid (Tetrac) did not affect T3 uptake after 15 min or after 24 h. Diiodothyropropionic acid (DITPA) (10 microM) reduced 15-min T3 uptake by about 24% (P<0.05), but it had a greater effect after 4 h (56%; P<0.001). Exposure to 10 nM DITPA during culture reduced cellular T3 uptake, as did 10 nM T3, suggesting down-regulation of the plasma membrane T3 transporters. We conclude that i) Triac is taken up by cardiomyocytes; ii) 3,3'-T2 and, to a lesser extent, DITPA and T4 interfere with plasma membrane transport of T3, whereas 3,5-T2, Triac, or Tetrac do not; iii) the transport mechanism for Triac is probably different from that for T3

Adaptive changes in transmembrane transport and metabolism of triiodothyronine in perfused livers of fed and fasted hypothyroid and hyperthyroid rats

The transport and subsequent metabolism of triiodothyronine (T3) were studied in isolated perfused livers of euthyroid, hypothyroid, and hyperthyroid rats, both fed and 48-hour-fasted. T3 kinetics (transport and metabolism) during perfusion were evaluated by a two-pool model, whereas the metabolism of T3 was also investigated by determination of T3 breakdown products by chromatography of medium and bile. For comparison of groups, metabolism was corrected for differences in transport. Transport parameters in fed hypothyroid livers were not significantly changed as compared with euthyroid livers, whereas metabolism was decreased. In fed hyperthyroid livers, fractional transfer rate constants for influx (k21) and efflux (k12) were decreased and metabolism, corrected for differences in intracellular mass transfer, was increased. Furthermore, for transport in hyperthyroid livers it was shown that only total mass transfer (TMT) into the metabolizing liver compartment (not into the nonmetabolizing liver compartment) was decreased. Transport and metabolic parameters in fasted hypothyroid livers were decreased as compared with euthyroid fed livers. In fasted hyperthyroid livers, transport and metabolism were not significantly different as compared with that in euthyroid fed livers, so transport was increased versus hyperthyroid fed livers. It appeared therefore that fasting normalized the effects of hyperthyroidism on both the transport and metabolic processes of T3 in the liver. The present study demonstrates normal transport and decreased metabolism in livers of hypothyroid fed rats and decreased transport and increased metabolism in livers of hyperthyroid fed rats. In livers of hypothyroid fasted rats transport and metabolism were decreased, whereas in livers of hyperthyroid fasted rats transport and metabolism were not significantly different from that in euthyroid fed livers. These changes might favor tissue euthyroidism despite the altered thyroid and nutritional state, and can therefore be seen as adaptation mechanisms to these altered states at the tissue level

Rapid sulfation of 3,3',5'-triiodothyronine in native Xenopus laevis oocytes

Sulfation is an important metabolic pathway facilitating the degradation of thyroid hormone by the type I iodothyronine deiodinase. Different human and rat tissues contain cytoplasmic sulfotransferases that show a substrate preference for 3,3'-diiodothyronine (3,3'-T2) > T3 > rT3 > T4. During investigation of the expression of plasma membrane transporters for thyroid hormone by injection of rat liver RNA in Xenopus laevis oocytes, we found uptake and metabolism of iodothyronines by native oocytes. Groups of 10 oocytes were incubated for 20 h at 18 C in 0.1 ml medium containing 500,000 cpm (1-5 nM) [125I]T4, [125I]T3, [125I]rT3, or [125I]3,3'-T2. In addition, cytosol prepared from oocytes was tested for iodothyronine sulfotransferase activity by incubation of 1 mg cytosolic protein/ml for 30 min at 21 C with 1 microM [125I]T4, [125I]T3, [125I]rT3, or [125I]3,3'-T2 and 50 microM 3'-phosphoadenosine-5'-phosphosulfate. Incubation media, oocyte extracts, and assay mixtures were analyzed by Sephadex LH-20 chromatography for production of conjugates and iodide. After 20-h incubation, the percentage of added radioactivity present as conjugates in the media and oocytes amounted to 0.9 +/- 0.2 and 1.0 +/- 0.1 for T4, less than 0.1 and less than 0.1 for T3, 32.5 +/- 0.4 and 29.3 +/- 0.2 for rT3, and 3.8 +/- 0.3 and 2.3 +/- 0.2 for 3,3'-T2, respectively (mean +/- SEM; n = 3). The conjugate produced from rT3 was identified as rT3 sulfate, as it was hydrolyzed by acid treatment. After injection of oocytes with copy RNA coding for rat type I iodothyronine deiodinase, we found an increase in iodide production from rT3 from 2.3% (water-injected oocytes) to 46.2% accompanied by a reciprocal decrease in rT3 sulfate accumulation from 53.7% to 7.1%. After 30-min incubation with cytosol and 3'-phosphoadenosine-5'-phosphosulfate, sulfate formation amounted to 1.8% for T4, less than 0.1% for T3, 77.9% for rT3, and 2.9% for 3,3'-T2. These results show that rT3 is rapidly metabolized in native oocytes by sulfation. The substrate preference of the sulfotransferase activity in oocytes is rT3 >> 3,3'-T2 > T4 > T3. The physiological significance of the high activity for rT3 sulfation in X. laevis oocytes remains to be established

Changes in renal tri-iodothyronine and thyroxine handling during fasting

OBJECTIVE: Liver handling of thyroid hormones (TH) has been known to alter significantly during fasting. This study investigates whether renal handling of TH is also changed during fasting. METHODS: We measured urinary excretion rates and clearances of free tri-iodothyronine (T(3)) and free thyroxine (T(4)) in healthy subjects prior to and on the third day of fasting. RESULTS: During fasting, both mean T(3) and T(4) urinary excretion decreased significantly to a mean value of 42% of control. Also, total and free (F) serum T(3) concentrations declined significantly, but serum T(4) did not change. Both FT(3) and FT(4) clearance decreased significantly during fasting (62% and 42% of control). The fasting-induced decrease in uric acid clearance correlated well with the decrease in FT(3) clearance (r=0.94; P<0.001). Serum concentrations of non-esterified fatty acids (NEFA) were significantly elevated during fasting. CONCLUSIONS: The findings cannot be fully explained by the fasting-induced decrease in serum T(3), a

Plasma membrane transport of thyroid hormones and its role in thyroid hormone metabolism and bioavailability

Although it was originally believed that thyroid hormones enter target cells by passive diffusion, it is now clear that cellular uptake is effected by carrier-mediated processes. Two stereospecific binding sites for each T4 and T3 have been detected in c

Effects of interleukin-1 beta on thyrotropin secretion and thyroid hormone uptake in cultured rat anterior pituitary cells

The effects of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF alpha) on basal and TRH-induced TSH release, and the effects of IL-1 beta on the uptake of [125I]T3 and [125I]T4 and on nuclear binding of [125I]T3 were examined. Furthermore, the release of other anterior pituitary hormones in the presence of IL-1 beta was measured. Anterior pituitary cells from male Wistar rats were cultured for 3 days in medium containing 10% FCS. Incubation were performed at 37 C in medium with 0.5% BSA for measurement of [125I]T3 uptake and with 0.1% BSA for measurement of [125I]T4 uptake. Exposure to IL-1 beta (1 pM-1 nM) or TNF alpha (100 pM) for 2-4 h resulted in a significant decline in TSH release, which was almost 50% (P < 0.05) for 1 nM IL-1 beta and 24% (P < 0.05) for 100 pM TNF alpha. Measurement of other anterior pituitary hormones (FSH, LH, PRL, and ACTH) in the same incubation medium showed that IL-1 beta did not alter their release. When the effects of IL-1 beta (1 pM-1 nM) and TNF alpha (100 pM) on TRH-induced TSH release were measured in short term experiments, the inhibitory effects had disappeared. The addition of 1-100 nM octreotide, a somatostatin analog, resulted in a decrease in TRH-induced TSH release up to 33% of the control value (P < 0.05). Exposure to dexamethasone (1 nM to 1 microM) affected basal and TRH-induced TSH release similar to the effect of IL-1 beta. The 15-min uptake of [125I]T3 and [125I]T4, expressed as femtomoles per pM free hormone, was not affected by the presence of IL-1 beta (1-100 pM). When IL-1 beta (100 pM) was present during 3 days of culture, TSH release was reduced to 88 +/- 2% of the control value (P < 0.05). This effect was not associated with an altered [125I]T3 uptake (15 min to 4 h) or with any change in nuclear T3 binding. We conclude that 1) IL-1 beta decreases TSH release by a direct action on the pituitary; 2) this effect is not due to elevated thyroid hormone uptake or increase T3 nuclear occupancy; 3) IL-1 beta does not affect TRH-induced TSH release or the release of other anterior pituitary hormones; and 4) TNF alpha affects basal and TRH-induced TSH release in the same way as IL-1 beta