Iodine deficiency associated with parenteral nutrition in extreme preterm infants.

Infants are in negative iodine balance on current standard regimens of total parenteral nutrition, with a mean iodine intake of 3 micro g/kg/day (150 ml/kg/day). The recommended enteral intake of iodine for preterm infants is 30 micro g/kg/day. Gastrointestinal absorption of iodine is high, suggesting that parenteral intakes should approach enteral recommendations.

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.

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), and are in accordance with inhibition of uptake of T(3) and T(4) at the basolateral membrane of the tubular cell. This inhibition may be caused by a decreased energy state of the tubular cell and by other factors such as ketoacidosis and/or increased NEFA concentrations during fasting.

Ontogeny of iodothyronine deiodinases in human liver.

The role of the deiodinases D1, D2, and D3 in the tissue-specific and time-dependent regulation of thyroid hormone bioactivity during fetal development has been investigated in animals but little is known about the ontogeny of these enzymes in humans. We analyzed D1, D2, and D3 activities in liver microsomes from 10 fetuses of 15-20 weeks gestation and from 8 apparently healthy adult tissue transplant donors, and in liver homogenates from 2 fetuses (20 weeks gestation), 5 preterm infants (27-32 weeks gestation), and 13 term infants who survived up to 39 weeks postnatally. D1 activity was determined using 1 microM [3',5'-125I]rT3 as substrate and 10 mM dithiothreitol (DTT) as cofactor, D2 activity using 1 nM [3',5'-125I]T4 and 25 mM DTT in the presence of 1 mM 6-propyl-2-thiouracil (to block D1 activity) and 1 microM T3 (to block D3 activity), and D3 activity using 10 nM [3,5-125I]T3 and 50 mM DTT, by quantitation of the release of 125I. The assays were validated by high performance liquid chromatography of the products, and kinetic analysis [Michaelis-Menten constant (Km) of rT3 for D1: 0.5 microM; Km of T3 for D3: 2 nM]. In liver homogenates, D1 activity was not correlated with age, whereas D3 activity showed a strong negative correlation with age (r -0.84), with high D3 activities in preterm infants and (except in 1 infant of 35 weeks) absent D3 activity in full-term infants. In microsomes, D1 activities amounted to 4.3-60 pmol/min/mg protein in fetal livers and to 170-313 pmol/min/mg protein in adult livers, whereas microsomal D3 activities were 0.15-1.45 pmol/min/mg protein in fetuses and <0.1 pmol/min/mg protein in all but one adult. In the latter sample, D3 activity amounted to 0.36 pmol/min/mg protein. D2 activity was negligible in both fetal and adult livers. These findings indicate high D1 and D3 activities in fetal human liver, and high D1 and mostly absent D3 activities in adult human liver. Therefore, the low serum T3 levels in the human fetus appear to be caused by high hepatic (and placental) D3 activity rather than caused by low hepatic D1 activity. The occasional expression of D3 in adult human liver is intriguing and deserves further investigation.

Possible role of corticosterone in the down-regulation of the hypothalamo-hypophysial-thyroid axis in streptozotocin-induced diabetes mellitus in rats.

We investigated the effects of diabetes mellitus on the hypothalamo-hypophysial-thyroid axis in male (R x U) F1 and R-Amsterdam rats, which were found to respond to streptozotocin (STZ)-induced diabetes mellitus with no or marked increases, respectively, in plasma corticosterone. Males received STZ (65 mg/kg i.v.) or vehicle, and were killed 1, 2 or 3 weeks later. At all times studied, STZ-induced diabetes mellitus resulted in reduced plasma TSH, thyroxine (T4) and 3,5,3'-tri-iodothyronine (T3). Since the dialyzable T4 fraction increased after STZ, probably as a result of decreased T4-binding prealbumin, plasma free T4 was not altered during diabetes. In contrast, both free T3 and its dialyzable fraction decreased during diabetes, which was associated with an increase in T4-binding globulin. Hepatic activity of type I deiodinase decreased and T4 UDP-glucuronyltransferase increased after STZ treatment. Thus, the lowered plasma T3 during diabetes may be due to decreased hepatic T4 to T3 conversion. Median eminence content of TRH increased after STZ, suggesting that hypothalamic TRH release is reduced during diabetes and that this is not caused by impaired synthesis or axonal transport of TRH to the median eminence. Hypothalamic proTRH mRNA did not change in diabetic (R x U) F1 rats during the period of observation, but was lower in R-Amsterdam rats 3 weeks after STZ. Similarly, pituitary TSH and TSH beta mRNA had decreased in R-Amsterdam rats by 1 week after STZ treatment, but did not change in (R x U) F1 rats. The difference between the responses in diabetic R-Amsterdam and (R x U) F1 rats may be explained on the basis of plasma corticosterone levels which increased in R-Amsterdam rats only. Hypothalamic TRH content was not affected by diabetes mellitus, but the hypothalami of diabetic rats released less TRH in vitro than those of control rats. Moreover, insulin had a positive effect on TRH release in vitro. In conclusion, the reduced hypothalamic TRH release during diabetes is probably not caused by decreases in TRH synthesis or transport to the median eminence, but seems to be due to impaired TRH release from the median eminence which may be related to the lack of insulin. Inhibition of proTRH and TSH beta gene expression in diabetic R-Amsterdam rats is not a primary event but appears to be secondary to enhanced adrenal activity in these animals during diabetes.

Gender-specific changes in thyroid hormone-glucuronidating enzymes in rat liver during short-term fasting and long-term food restriction.

Glucuronidation is a major pathway of thyroid hormone metabolism in rats, involving at least three different hepatic UDP-glucuronyltransferases (UGTs): bilirubin UGT, phenol UGT and androsterone UGT. We have studied the effects of short-term (3 days) fasting and long-term (3 weeks) food restriction to one-third of normal intake (FR33) on hepatic UGT activities for thyroxine (T4), triiodothyronine (T3), bilirubin and androsterone in male and female Wistar rats with either a functional (high activity, HA) or a defective (low activity, LA) androsterone UGT gene. Because food deprivation is known to induce centrally mediated hypothyroidism in rats, results were compared with those obtained in methimazole (MMI)-induced hypothyroid rats. Both fasting and FR33 produced largely parallel increases in T4 and bilirubin UGT activities. These effects were greater in males than in females, and were reproduced in MMI-treated rats. In male and female HA rats, fasting induced insignificant increases in T3 UGT activity and had no effect on androsterone UGT activity. In male HA rats, FR33 was associated with an increase in T3 UGT activity, while androsterone UGT activity showed little change. However, in female HA rats both T3 and androsterone UGT activities were markedly decreased by FR33. Triiodothyronine UGT activity in LA rats was strongly decreased compared with HA rats, but was not further decreased by FR33 in female LA rats, supporting the importance of androsterone UGT for T3 glucuronidation. These results demonstrate different sex-dependent effects of food deprivation on hepatic T4 and T3 glucuronidation that are associated with changes in the expression of bilirubin UGT and androsterone UGT, respectively. For the increased T4 and bilirubin UGT activities at least, these effects appear to be mediated by the hypothyroid state of the (semi)starved animals.

Effects of long-term food reduction on the hypothalamus-pituitary-thyroid axis in male and female rats.

The reduced thyroid activity during short-term starvation is associated with a lowered hypothalamic synthesis and secretion of TRH. However, little is known about the cause of the reduced thyroid function during prolonged malnutrition. We have therefore studied the effects of food reduction to one-third of normal (FR33) on the hypothalamus-pituitary-thyroid axis of male and female Wistar rats. After 3 weeks body weights of FR33 rats were almost 50% lower than those of controls. In both sexes, FR33 caused marked increases in serum corticosterone, and decreases in serum TSH, thyroxine (T4), free T4, tri-iodothyronine (T3) and free T3. While the free T3 fraction (FFT3) in serum decreased, the free T4 fraction (FFT4) tended to increase. Electrophoretic analysis indicated that decreased FFT3 was correlated with an increased thyroxine-binding globulin, while the increase in FFT4 seemed due to a decreased thyroxine-binding prealbumin binding capacity. Total RNA and proTRH mRNA in the hypothalamus were not affected by FR33. Median eminence and posterior pituitary TRH content tended to increase in FR33 rats, suggesting that hypothalamic TRH release is reduced in FR33 rats. Anterior pituitary TSH content was decreased by FR33 in both sexes, but pituitary TSH beta mRNA and TRH receptor status were not affected except for increased pituitary TSH beta mRNA in female FR33 rats. Although FR33 had no effect on pituitary weight, pituitary RNA and membrane protein content in FR33 rats were 50-70% lower than values in controls. In conclusion, prolonged food reduction suppresses the pituitary-thyroid axis in rats. In contrast to short-term food deprivation, the mechanism whereby serum TSH is suppressed does not appear to involve decreases in proTRH gene expression, but may include effects on pituitary mRNA translation. Our results further support the hypothesis that TSH release may be lowered by increased corticosterone secretion, although the mechanism of this effect may differ between acute starvation and prolonged food reduction.

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.

Studies on the role of TRH and corticosterone in the regulation of prolactin and thyrotrophin secretion during lactation.

This study describes the effects of litter size and acute suckling on the synthesis and release of hypothalamic TRH, as indirectly estimated by determination of hypothalamic prothyrotrophin-releasing hormone (proTRH) mRNA and median eminence TRH content. The effects of litter size (five or ten pups) were studied throughout lactation, while suckling-induced acute changes were analyzed on day 13 of lactation in dams with ten pups. In view of the enhanced adrenal activity during lactation and recent evidence that corticosteroids have negative effects on hypothalamic TRH, we also studied adrenalectomized (ADX) dams treated with corticosterone to maintain basal plasma corticosterone levels. In addition to an increased plasma level of prolactin (PRL), adrenal weight and plasma corticosterone increased, while plasma TSH, tri-iodothyronine (T3), thyroxine (T4) and free T4 (FT4) levels decreased during lactation. Litter size correlated positively with plasma PRL, adrenal weight and plasma corticosterone. No effect of litter size was observed on plasma T3, but rats with ten pups had lower plasma TSH, T4 and FT4 than rats with a five-pup litter. Compared with dioestrous rats, lactating rats showed an increased hypothalamic proTRH mRNA content on day 2, but not on days 8 and 15 of lactation. Median eminence TRH in lactating rats gradually increased until day 15 and decreased thereafter. Acute suckling, after a 6-h separation of mother and pups, rapidly increased plasma PRL and corticosterone in the mothers, but had no effects on plasma TSH and thyroid hormone levels. Hypothalamic proTRH mRNA increased twofold after 0.5 h of suckling, and then gradually returned to presuckling values after 6 h. Compared with sham-operated rats, corticosterone-substituted ADX rats with ten pups had increased plasma PRL and TSH, hypothalamic proTRH mRNA and pituitary TSH beta mRNA on day 15 of lactation. Moreover, while acute suckling did not enhance TSH release in sham-operated rats, it provoked not only PRL but also TSH release in corticosterone-substituted ADX dams. It is concluded that suckling exerts a rapid, positive effect on hypothalamic proTRH mRNA content. However, the concurrent enhanced adrenal activity has negative effects on hypothalamic proTRH gene expression resulting in a suppressed hypophysial-thyroid axis during lactation. While TRH appears to play a role in PRL release during the first days of lactation and during acute suckling, TRH seems not important in maintaining PRL secretion during continued suckling.

Somatostatin receptor scintigraphy in non-medullary thyroid cancer.

8 patients with papillary cancer (4 with metastases, 4 in remission), 7 follicular cancer patients (6 with metastases), 2 patients with anaplastic thyroid cancer and 4 other non-medullary thyroid cancer patients all received an intravenous bolus injection of 220 MBq [111In-DTPA-D-Phe1]octreotide. Planar anterior and posterior gamma camera images of head-neck, chest and abdomen were obtained 24 and 48 h after injection. All primary cancers showed [111In-DTPA-D-Phe1] octreotide uptake; none occurred in patients in remission. The results were compared with conventional radio-iodine scintigraphy in patients with metastasised, differentiated thyroid cancer.

Uptake of 3,3',5,5'-tetraiodothyroacetic acid and 3,3',5'-triiodothyronine in cultured rat anterior pituitary cells and their effects on thyrotropin secretion.

We compared the uptake, metabolism, and biological effects of tetraiodothyroacetic acid (Tetrac) and rT3 in anterior pituitary cells with those of T4 and T3. Cells were isolated from adult male Wistar rats and cultured for 3 days in medium with 10% fetal calf serum. Uptake was measured at 37 C in medium with 0.1% BSA for [125I]Tetrac (200,000 cpm; 240 pM) and [125I]T4 (100,000 cpm; 175 pM) or with 0.5% BSA for [125I]rT3 (100,000 cpm; 250 pM) and [125I]T3 (50,000 cpm; 50 pM). The free fraction of Tetrac was 1% that of T4 (in medium with 0.1 and with 0.5% BSA), and the free fraction of rT3 was half that of T3. Uptake of the four tracers increased sharply up to 1 h of incubation and then leveled off. Expressed as femtomoles per pM free hormone, uptake at equilibrium was 1.16 +/- 0.16 (n = 6) for Tetrac, 0.15 +/- 0.01 (n = 6) for T4, 0.023 +/- 0.003 (n = 6) for rT3, and 0.21 +/- 0.02 (n = 6) for T3. Cell-associated radioactivity after incubation for 24 h with [125I]Tetrac was represented for 15% by [125I]Triac; after incubation with [125I]T4 for 15-20% by [125I]T3, after incubation with [125I]rT3 for 6% by [125I]3,3'-T2, while [125I]T3 was still for 98% [125I]T3. Exposure of cells for 2 h to 100 nM TRH stimulated TSH release by 90-135%. Tetrac was effective in reducing this response at a free concentration of 0.05 pM, but rT3 was effective only at a free concentration of 16 nM. A free Tetrac concentration of 5 pM was equally effective as 50 pM free T4 in reducing the TSH response to TRH. In human serum, Tetrac was exclusively bound to T4-binding prealbumin. The free Tetrac fraction was 0.001% in control subjects and rose 2- to 12-fold in patients with nonthyroidal illness. As uptake of [125I]Tetrac in the pituitary was higher than that of T4 and T3, and it was more potent than T4 in reducing TSH release, Tetrac may be of potential significance for the regulation of TSH secretion in vivo.

Starvation-induced changes in the hypothalamic content of prothyrotrophin-releasing hormone (proTRH) mRNA and the hypothalamic release of proTRH-derived peptides: role of the adrenal gland.

The purpose of this study was to investigate the mechanisms involved in the reduced thyroid function in starved, young female rats. Food deprivation for 3 days reduced the hypothalamic content of prothyrotrophin-releasing hormone (proTRH) mRNA, the amount of proTRH-derived peptides (TRH and proTRH160-169) in the paraventricular nucleus, the release of proTRH-derived peptides into hypophysial portal blood and the pituitary levels of TSH beta mRNA. Plasma TSH was either not affected or slightly reduced by starvation, but food deprivation induced marked increases in plasma corticosterone and decreases in plasma thyroid hormones. Refeeding after starvation normalized these parameters. Since the molar ratio of TRH and proTRH160-169 in hypophysial portal blood was not affected by food deprivation, it seems unlikely that proTRH processing is altered by starvation. The median eminence content of pGlu-His-Pro-Gly (TRH-Gly, a presumed immediate precursor of TRH), proTRH160-169 or TRH were not affected by food deprivation. Since median eminence TRH-Gly levels were very low compared with other proTRH-derived peptides it is unlikely that alpha-amidation is a rate-limiting step in hypothalamic TRH synthesis. Possible negative effects of the increased corticosterone levels during starvation on proTRH and TSH synthesis were studied in adrenalectomized rats which were treated with corticosterone in their drinking water (0.2 mg/ml). In this way, the starvation-induced increase in plasma corticosterone could be prevented. Although plasma levels of thyroid hormones remained reduced, food deprivation no longer had negative effects on hypothalamic proTRH mRNA, pituitary TSH beta mRNA and plasma TSH in starved adrenalectomized rats. Thus, high levels of corticosteroids seem to exert negative effects on the synthesis and release of proTRH and TSH. This conclusion is corroborated by the observation that TRH release into hypophysial portal blood became reduced after administration of the synthetic glucocorticosteroid dexamethasone. On the basis of these results, it is suggested that the reduced thyroid function during starvation is due to a reduced synthesis and release of TRH and TSH. Furthermore, the reduced TRH and TSH synthesis during food deprivation are probably caused by the starvation-induced enhanced adrenal secretion of corticosterone.

Uptake of triiodothyroacetic acid and its effect on thyrotropin secretion in cultured anterior pituitary cells.

The uptake of [125I]triiodothyroacetic acid ([125I]Triac) in anterior pituitary cells was investigated and compared with that of [125I]T3. Furthermore, the effects of Triac, T3, and T4 on TSH release were compared. Cells isolated from adult male Wistar rats were cultured for 3 days in medium with 10% fetal calf serum. Uptake was measured at 37 C with [125I]Triac (100,000 cpm; 120 pM) or [125I]T3 (50,000 cpm; 50 pM) in medium with 0.5% BSA. In this medium, the ratio of the free fractions of Triac, T3, and T4 was 1:8:1. Exposure of cells to 100 nM TRH for 2 h stimulated TSH release by 80-110% (P < 0.001). Comparing total hormone levels (1 nM to 1 microM), Triac and T3 were equally effective in reducing this response, and both were 10-fold more effective than T4. The time course (15 min to 4 h) of [125I]Triac uptake was similar to that of [125I]T3, showing equilibrium after 1 h. Unlabeled Triac (1 microM) reduced the uptake of [125I]Triac and [125I]T3 at all time intervals. Expressed per pM free hormone, the cellular and nuclear uptake of [125I]Triac were twice those of [125I]T3. The 15-min uptake of [125I]Triac was reduced by incubation with 10 nM unlabeled Triac (35%; P < 0.001). Maximum inhibition (56%; P < 0.001) was found with 10 microM Triac. A similar effect was seen with 10 microM T3, T4, or 3,3',5,5'-tetraiodothyroacetic acid. Preincubation (30 min) and incubation (15 min) with 10 microM oligomycin reduced the cellular ATP content by 51% (P < 0.001), [125I]T3 uptake by 77% (P < 0.001), and [125I]Triac uptake by only 25% (P < 0.001). The temperature dependence of [125I]Triac and [125I]T3 uptake was the same. Preincubation and incubation with 10 microM monensin (reduces the Na+ gradient) or 10 microM monodansylcadaverine (inhibits receptor-mediated endocytosis) reduced 15-min [125I] Triac uptake by 15% (P < 0.005) and 19% (P < 0.005), respectively. The data show that 1) Triac, on the basis of the free hormone concentration, is more potent than T3 or T4 in suppressing TSH secretion; and 2) the rapid uptake of [125I]Triac by the anterior pituitary occurs by a carrier-mediated mechanism that is only partially dependent on ATP or the Na+ gradient.

Different effects of continuous infusion of interleukin-1 and interleukin-6 on the hypothalamic-hypophysial-thyroid axis.

The cytokines interleukin-1 (IL-1) and IL-6 are thought to be important mediators in the suppression of thyroid function during nonthyroidal illness. In this study we compared the effects of IL-1 and IL-6 infusion on the hypothalamus-pituitary-thyroid axis in rats. Cytokines were administered by continuous ip infusion of 4 micrograms IL-1 alpha/day for 1, 2, or 7 days or of 15 micrograms IL-6/day for 7 days. Body weight and temperature, food and water intake, and plasma TSH, T4, free T4 (FT4), T3, and corticosterone levels were measured daily, and hypothalamic pro-TRH messenger RNA (mRNA) and hypophysial TSH beta mRNA were determined after termination of the experiments. Compared with saline-treated controls, infusion of IL-1, but not of IL-6, produced a transient decrease in food and water intake, a transient increase in body temperature, and a prolonged decrease in body weight. Both cytokines caused transient decreases in plasma TSH and T4, which were greater and more prolonged with IL-1 than with IL-6, whereas they effected similar transient increases in the plasma FT4 fraction. Infusion with IL-1, but not IL-6, also induced transient decreases in plasma FT4 and T3 and a transient increase in plasma corticosterone. Hypothalamic pro-TRH mRNA was significantly decreased (-73%) after 7 days, but not after 1 or 2 days, of IL-1 infusion and was unaffected by IL-6 infusion. Hypophysial TSH beta mRNA was significantly decreased after 2 (-62%) and 7 (-62%) days, but not after 1 day, of IL-1 infusion and was unaffected by IL-6 infusion. These results are in agreement with previous findings that IL-1, more so than IL-6, directly inhibits thyroid hormone production. They also indicate that IL-1 and IL-6 both decrease plasma T4 binding. Furthermore, both cytokines induce an acute and dramatic decrease in plasma TSH before (IL-1) or even without (IL-6) a decrease in hypothalamic pro-TRH mRNA or hypophysial TSH beta mRNA, suggesting that the acute decrease in TSH secretion is not caused by decreased pro-TRH and TSH beta gene expression. The TSH-suppressive effect of IL-6, either administered as such or induced by IL-1 infusion, may be due to a direct effect on the thyrotroph, whereas additional effects of IL-1 may involve changes in the hypothalamic release of somatostatin or TRH.(ABSTRACT TRUNCATED AT 400 WORDS)

T4 uptake into the perfused rat liver and liver T4 uptake in humans are inhibited by fructose.

Recently, we described a two-pool model for 3,5,3'-triiodothyronine uptake and metabolism in the isolated perfused rat liver. Here, we applied this model to investigate transmembrane thyroxine (T4) transport and its possible ATP dependence in vivo. These studies are performed in perfused rat livers during perfusion with or without fructose in the medium, as it has been shown that intracellular ATP is decreased after fructose loading. Furthermore, we studied serum T4 tracer disappearance curves in four human subjects before and after intravenous fructose loading. In the perfused rat liver, we found a decrease in liver ATP concentration and a decrease in medium T4 disappearance and T4 uptake in the liver pool after fructose. Furthermore, it was shown that, when corrected for differences in the medium free hormone concentration, only transport to the metabolizing liver pool was decreased after fructose perfusion, whereas uptake in the nonmetabolizing pool was unaffected. Disposal, corrected for differences in transport into the metabolizing pool, was also not affected after fructose. In the human studies, intravenous fructose administration induced a rise in serum lactic acid and uric acid, indicating a decrease in liver ATP. This was observed concomitant with a decrease in serum tracer T4 disappearance during the first 3 h after fructose administration. These results suggest ATP dependence of transport of iodothyronines into the liver in vivo and show that, in the rat liver and in humans, uptake of T4 may be regulated by intracellular energy stores; in this way the tissue uptake process may affect intracellular metabolism and bioavailability of thyroid hormone.

Transport of thyroxine into cultured hepatocytes: effects of mild non-thyroidal illness and calorie restriction in obese subjects.

OBJECTIVE: Inhibitors of cellular T4 transport leading to diminished plasma T3 production have been identified as 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) and indoxyl sulphate in uraemia and bilirubin and non-esterified fatty acids (NEFA) in critically ill patients with hyperbilirubinaemia. We question whether other factors are responsible for the altered thyroid hormone parameters observed in mild illness and during calorie restriction. PATIENTS: We studied (i) 18 non-uraemic patients with non-thyroidal illness (NTI) (T4 > or = 60, T3 < or = 1.1 and rT3 > or = 0.45 nmol/l) with serum molar ratios of bilirubin:albumin < or = 0.17 and NEFA:albumin < or = 2.6. These molar ratios have been shown to be the minimum ratios which inhibited T4 transport into rat hepatocytes; (ii) four obese euthyroid subjects on 600 kcal/day for 10-14 days. This diet is known to inhibit the unidirectional T4 transport into human liver in vivo. MEASUREMENTS: We measured iodide production from 125I-T4 by incubating rat hepatocytes with 10% human serum. The deiodination of T4 was used as an index of cellular transport of T4 in vivo. RESULTS: The mean iodide production from 125I-T4 by rat hepatocytes in the presence of 10% serum from NTI patients (98 +/- 17%, mean +/- SD) was not significantly different from the normals (100 +/- 9%). Calorie restriction in euthyroid obese subjects resulted in a small but significant reduction (-12%) of iodide production. Calorie restriction increased the total serum NEFA by 91%. CONCLUSIONS: Our study demonstrates that CMPF, indoxyl sulphate, bilirubin and NEFA are not responsible for the inhibition of T4 tissue uptake in patients with mild illness. In addition, studies with calorie restricted obese subjects indicate that high concentration of NEFA during calorie restriction inhibits T4 tissue uptake. This inhibition may partly explain the lower plasma T3 during calorie restriction.

Glucuronidation of thyroid hormone in rat liver: effects of in vivo treatment with microsomal enzyme inducers and in vitro assay conditions.

We investigated the effects of in vivo treatment with different microsomal enzyme inducers, including clofibrate (CLOF), hexachlorobenzene (HCB), 3-methylcholanthrene (MC), 3,3',4,4'-tetrachlorobiphenyl (TCB), and 2,3,7,8-tetrachloro-p-dioxin, as well as of in vitro addition of the detergent Brij 56 on the glucuronidation of T4, T3, and rT3 by UDP-glucuronyltransferase (UGT) activities of rat liver microsomes. The results were compared with measurements of UGT activities for bilirubin, p-nitrophenol (PNP), and androsterone. In general, glucuronidation rates were 5-fold or more higher with rT3 than with T4 or T3 as substrate. In liver microsomes from untreated rats, T4 UGT activity was stimulated by Brij 56 to a maximum of about 2-fold at 0.025% detergent. Treatment of Wistar rats for 4 days with CLOF (200 mg/kg BW.day) resulted in significant increases in UGT activities for T4 (to 154%), rT3 (to 155%), and bilirubin (to 194%), in particular if assayed in the presence of 0.025% Brij 56, but had little effect on the UGT activities for T3, PNP, and androsterone. The CLOF-induced increases in T4 and rT3 UGT activities were not observed in Gunn rats, which have a complete lack of bilirubin UGT activity and greatly impaired PNP UGT activity. Treatment of Wistar rats with a single injection of MC (50 mg/kg BW), TCB (50 mg/kg BW), or 2,3,7,8-tetrachloro-p-dioxin (6.25 micrograms/kg BW) resulted, after 4 days, in 6.3- to 7.3-fold increases in T4 UGT activity and 15.1- to 16.7-fold increases in rT3 UGT activity if determined in the absence of Brij 56, whereas T4 UGT activity was only increased by 33-68% when assayed in the presence of Brij 56. T3 glucuronidation was not affected (with Brij 56) or was increased by only 33-68% (without Brij 56) after treatment with these MC-type inducers. PNP UGT activity was induced 3.6- to 4.3-fold, whereas bilirubin and androsterone UGT activities were changed little by these treatments. Similar findings regarding T4, rT3, PNP, and bilirubin UGT activities were obtained after chronic treatment of WAG rats with HCB, another MC-type inducer. However, WAG rats lack androsterone UGT and show low T3 UGT activity, which was increased about 2.3-fold by HCB treatment. On the basis of these and previous findings it is concluded that at least three UGT isoenzymes are involved in the glucuronidation of thyroid hormone.(ABSTRACT TRUNCATED AT 400 WORDS)

Free thyroxine assessed with three assays in sera of patients with nonthyroidal illness and of subjects with abnormal concentrations of thyroxine-binding proteins.

Three methods for estimating free thyroxine (FT4) in serum were studied: equilibrium dialysis, the SPAC-ET FT4 radioimmunoassay kit, and the Amerlite MAB FT4 luminometric assay. Serum samples from 10 subjects with above-normal thyroxine-binding globulin (TBG), 6 with low TBG, 30 with familial dysalbuminemic hyperthyroxinemia (FDH), 13 with nonesterified fatty acids (NEFA) concentrations in serum > 1.0 mmol/L, and 178 patients with various degrees of nonthyroidal illness (NTI) were measured and compared with samples from 42 euthyroid blood donors. The Amerlite MAB FT4 assay compared well with equilibrium dialysis, whereas the SPAC-ET assay averaged 40% lower. All three assays were not influenced by changes in TBG and showed no or only little changes in the presence of NEFA. Mean FT4 values in the FDH samples were somewhat higher than in controls when measured with the SPAC-ET assay, about equal with equilibrium dialysis, and somewhat below the mean control value with the Amerlite MAB FT4 assay, although individual results were within the control reference range. In NTI patients, no FT4 values were below the control reference range by the Amerlite MAB FT4 assay, 4 of 178 were below this range by equilibrium dialysis, and 1 of 178 was below this range by the SPAC-ET assay. In all assays a large proportion of the NTI samples showed FT4 values above the control reference range, a result that will interfere with the efficacy of these assays for assessing thyroid function in NTI patients.

Inhibition of thyroxine transport into cultured rat hepatocytes by serum of nonuremic critically ill patients: effects of bilirubin and nonesterified fatty acids.

We investigated bilirubin and oleic acid as causes of low plasma T3 in nonuremic critically ill patients with gross changes in serum thyroid hormone levels (T4, < or = 60; T3, < or = 1.1; rT3, > or = 0.45 nmol/L) and elevated bilirubin concentrations (> or = 33 mumol/L). Iodide production from [125I]T4 was inhibited by 42% when rat hepatocytes in primary cultures were incubated with 10% serum from these patients. The mean serum concentration of albumin was reduced by 41%, while the concentrations of bilirubin and nonesterified fatty acids (NEFA) were increased by 2022% and 115%, respectively, in the patients. The molar ratios of bilirubin/albumin and NEFA/albumin in the patients were 0.42 and 3.18, respectively. Addition of oleic acid (50-400 mumol/L) and bilirubin (3-130 mumol/L) to 10% normal human serum (albumin, 70 mumol/L; NEFA, 54 mumol/L; bilirubin, 1.1 mumol/L) progressively inhibited the production of iodide by rat hepatocytes. The decreased iodide production was presumed to be caused by inhibition of T4 transport into hepatocytes. The deiodination of rT3 by rat liver microsomes was unaltered by free bilirubin and free oleic acid concentrations up to 0.1 mumol/L. These free concentrations are at least 1 order of magnitude higher than that attained in nonthyroidal illness. The inhibition of iodide production by the sera of critically ill patients (n = 12) was significantly correlated with the molar ratios of bilirubin/albumin (r = 0.72; P < 0.01) and NEFA/albumin (r = 0.58; P < 0.05). Extensive dialysis or treatment of the sera with charcoal did not completely remove the inhibitory activity on iodide production. Serum concentrations of indoxyl sulfate, 3-carboxy-4-methyl-5-propyl-2-furan propanoic acid, and hippuric acid in the critically ill patients (other known T4 transport inhibitors into hepatocytes) were similar to those in the normal subjects. This study together with the well known effects of carbohydrate on T3 neogenesis suggest that elevated bilirubin and NEFA and the low albumin level in non-uremic critical illness may be at least partly responsible for the T4 transport inhibition in T3-producing tissues (e.g. the liver) and, thus, the low plasma T3 levels in these critically ill patients. The question of whether inhibitors of T4 transport into the hepatocytes are also present in other patients with nonthyroidal illness who show only mild changes in thyroid hormone levels and have low concentrations of bilirubin and NEFA remains to be determined.

Effect of starvation and subsequent refeeding on thyroid function and release of hypothalamic thyrotropin-releasing hormone.

Effects of starvation on thyroid function were studied in 5- to 6-week-old (R x U) F1 rats. Starvation lowered plasma TSH in female, but not in male rats. Plasma T4 and T3 levels decreased, whereas the dialysable T4 fraction increased during starvation. Free T4 (FT4) levels decreased rapidly in females, but only after prolonged fasting in male rats. Glucose decreased, and free fatty acid levels increased during starvation. Peripheral TRH levels did not change during food deprivation. Since effects of starvation were most apparent in young female rats, such rats were used to study hypothalamic TRH release during starvation and subsequent refeeding. Basal in vitro hypothalamic TRH secretion was less in starved rats than in control or refed animals. In vitro hypothalamic TRH release in medium with 56 mM KCl increased 3-fold compared to basal release, and in these depolarization conditions TRH release was similar between hypothalami from control, starved and refed rats. In rats starved for 2 days, TRH level in hypophysial portal blood was lower than that of controls. Thus, diminished thyroid function during starvation may at least in part be caused by a reduced hypothalamic TRH release.