Effects of acute lindane intoxication and thyroid hormone administration in relation to nuclear factor-κB activation, tumor necrosis factor-α expression, and Kupffer cell function in the rat

Nuclear factor-kappaB (NF-kappaB) DNA binding, tumor necrosis factor-alpha (TNF-alpha) expression, and parameters related to liver oxidative stress and Kupffer cell function were assessed in control rats and in animals given 3,3',5-triiodothyronine (T3) (0.1 mg T3/kg) and/or lindane (50 mg/kg; 4 h after T3). Liver NF-kappaB DNA binding and serum TNF-alpha levels were enhanced by the combined T3-lindane administration after 16-22 h, effects that were lower than those elicited by the separate treatments and coincided with increased hepatic TNF-alpha mRNA levels. Thyroid calorigenesis occurred independently of lindane, whereas T3, lindane and T3-lindane groups showed liver glutathione (GSH) depletion, with higher protein carbonyl levels in lindane and T3-lindane groups. Carbon-induced O2 consumption/carbon uptake ratios were not altered by T3 or lindane compared to controls, whereas combined T3-lindane administration elicited a 92% diminution with enhancement in the sinusoidal efflux of lactate dehydrogenase (LDH). In conclusion, depression of T3- or lindane-induced liver NF-kappaB activation and TNF-alpha expression occurred after their combined treatment, effects that correlate with the impairment of the respiratory burst activity of Kupffer cells and exacerbation of liver injury.

Effects of thyroid hormone on food intake, hypothalamic Na/K ATPase activity and ATP content

The effects of thyroid hormone on whole body energy metabolism and compensatory effects on food intake are well established. However, the hypothalamic mechanisms that translate perceived whole body energy demands into subsequent appetitive behavior are incompletely understood. In order to address this question, we tested the effects of T3 on food intake and body weight in rats and measured neuronal Na/K ATPase activity and ATP content in the hypothalamus. Intraperitoneal T3 (100 microg/kg BW) administered for 6 consecutive days increased 24-h rat food intake from control, 26.6+/-1.2, to T3-treated 33.2+/-1.6 g (P<0.01). In T3-treated rats, rubidium-86 (86Rb) uptake (measured as a marker of Na/K ATPase activity) in ex vivo hypothalamic tissue increased (P<0.01) while the content of ATP in the ventral hypothalamus declined following T3 treatment (P<0.01). In another model of energy deficit, which was induced by a very low calorie diet, ATP content was also reduced in the hypothalamus compared to rats fed ad libitum. In summary, increased food intake in response to T3 may be secondary to decreased hypothalamic ATP content, perhaps resulting from both increased Na/K ATPase activity in the hypothalamus and metabolic signaling induced by whole body caloric deficit.

Hyperthyroidism Causes Mechanical Insufficiency of Myocardium with Possibly Increased SR Ca2+-ATPase Activity

Hyperthyroidism is known to affect multiple organ functions, and thyroid hormone has been known to improve myocardial function in a failing heart. The purpose of this study is to elucidate the functional and metabolic effects of thyroid hormone on myocardium in a rat model exposed to long-term excess thyroid hormone, particularly focusing on the SR Ca(2+)-ATPase (SERCA2) function. 3,5,3'-Triiodo-L-thyronine (T3), or the vehicle, was subcutaneously given for 4 weeks (T3 and control [C] group). Bolus I.V. Thapsigargin (TG) was used to test the SERCA2 function (C-TG and T3-TG) in Langendorff perfused heart. Myocardial functions such as LV-developed pressure (LVDP; mmHg), +/- dP/dt (mmHg/s), tau (ms), and oxygen consumption (MVO(2); ml/min/g wt) were measured. SERCA2 and GLUT4 protein level were also evaluated by Western immunoblotting. Left ventricle to body weight (LV/BW) ratio was significantly higher in the T3 group. Both negative dP/dt and tau were significantly decreased by TG. It is interesting that the decrement of negative dP/dt and tau attained by TG was significantly larger in the hyperthyroid group (T3-TG) than in a normal heart (C-TG). SERCA2 and GLUT4 protein levels were not significantly different between control and the T3 group. We conclude that prolonged exposure to thyroid hormone causes hypertrophy of the myocardium and an augmentation of the SR Ca(2+) ATPase activity. Care must be taken in hyperthyroid heart during the ischemia-reperfusion process where the SRECA2 function is inhibited.

Reverse 3,3',5'-triiodothyronine suppresses increase in free fatty acids in chickens elicited by dexamethasone or adrenaline

Reverse triiodothyronine (rT3) displays hypometabolic properties and antagonizes the hypermetabolic effect of 3,5,3'-triiodothyronine (T3). Previous experiments revealed that exogenous rT3 enhanced free fatty acids (FFA) in heat-stressed pullets and in chickens infected with lipopolysaccharide from Escherichia coli. To gain more data concerning the action of rT3, its effect on lipaemia produced by two main stress hormones: glucocorticoids and catecholamines, has been investigated. Synthetic glucocorticoid [dexamethasone (Dex)] and adrenaline (Adr) were used in two experiments. The experiments differed in duration, i.e. 24 h (Dex) or 150 min (Adr), and frequency of rT3 injections, i.e. two (Dex) or single (Adr) injections. The doses of hormones were as follows: rT3: 14 microg 100 g body weight/ injection (subcutaneously): Dex: 5 mg/animal (subcutaneously) and Adr: 1 mg/animal (intramuscularly). Maximal increases in FFA of 230.5 and 227.5% were noted after 1.5 and 3 h, respectively, in birds treated with Dex. Reverse T3 almost completely suppressed the rise of plasma FFA elicited by Dex. The increase in Dex + rT3-treated fowl was only 30.4% (not significant in comparison to control). Adr increased FFA by a maximum of 89.1 % and treatment with rT3 (Adr + rT3 group) suppressed this FFA increase to 42.5%. The data obtained demonstrate that rT3 suppresses lipaemia induced by an exogenous glucocorticoid and adrenaline. This suppression was more pronounced in glucocorticoid-treated birds, where Dex produced a higher lipolytic response than Adr.

Thyroid hormone acts centrally to programme photostimulated male american tree sparrows (Spizella arborea) for vernal and autumnal components of seasonality

Thyroid hormone and long days interact to programme American tree sparrows (Spizella arborea) for seasonality (i.e. thyroid hormone-dependent photoperiodic gonadal growth, photorefractoriness, and postnuptial moult). This study explored in radiothyroidectomized (THX) males given thyroid hormone replacement therapy whether thyroid hormone acts within the brain and, additionally, the identity of the putative tissue-active thyroid hormone. The minimum dose (30 ng) of L-thyroxine (T4) that restored all components of seasonality when given i.c.v. daily during the first 21 days of photostimulation restored no component of seasonality when given s.c. The same dose of L-triiodothyronine (T3) also was ineffective when administered s.c., but restored photoperiodic testicular growth (though neither photorefractoriness nor postnuptial moult) when admiministered i.c.v. Three of seven birds given a 10-fold lower dose of T4 (3 ng) exhibited thyroid hormone-dependent photoperiodic testicular growth, albeit damped. The other four birds given 3 ng T4 and all birds given 3 ng T3 responded like THX controls, exhibiting only slight thyroid hormone-independent photoperiodic testicular growth. The highest dose (300 ng) of T3 restored all components of seasonality only when administered i.c.v. daily during the first 49 days of photostimulation. This demonstration in American tree sparrows is the first in any species that the thyroid-dependent transition from the breeding season to the non-breeding season can be effected by T3. The same dose of reverse T3 administered daily over the same 49 days restored photoperiodic testicular growth in only half of 10 subjects and photorefractoriness and moult in none. Collectively, the data support the hypothesis that thyroid hormone acts centrally to programme photostimulated male American tree sparrows for all components of seasonality. The most parsimonious interpretation of the data, including the threshold-like effect of 3 ng T4, favours T4 as the tissue-active thyroid hormone for vernal as well as autumnal events, but does not entirely exclude T3.

Role of thyroid hormone in the control of growth hormone gene expression

Growth hormone (GH) gene expression was examined in male Wistar rats (200 g) subjected to different manipulations of thyroid status. Thyroidectomy followed by 10 days of treatment with 0.03% methimazole added to drinking water caused a marked decrease in GH mRNA levels estimated by Northern Blot analysis. T3 administration (100 micrograms/100 g body weight, ip, twice daily) to euthyroid rats for one week caused a substantial increase in GH mRNA levels. In another set of experiments, thyroidectomized methimazole-treated rats were killed at different times after a single T3 injection (100 micrograms/100 g body weight, ip). T3 induced a prompt response in GH gene expression by 15 min that reached a maximum after 1 h, remaining so up to 4 h. We conclude that in the rat, GH gene expression is highly dependent on thyroid hormones. Because of the rapidity of the response, the effect is probably mediated by a transcriptional mechanism.

Comparison of maternal to fetal transfer of 3,5,3'-triiodothyronine versus thyroxine in rats, as assessed from 3,5,3'-triiodothyronine levels in fetal tissues

Thyroxine (T4) is transferred from the mother to the hypothyroid rat fetus late in gestation, mitigating T4 and T3 deficiency in fetal tissues, the brain included. We have now compared the effects of maternal infusion with T3. Normal and thyroidectomized rats were started on methimazole (MMI) on the 14th day of gestation, given alone, or together with a constant infusion of 0.45 micrograms (0.69 nmol) T3 or of 1.8 microgram (2.3 nmol) T4/100 g per day. Maternal and fetal samples were obtained at the 21st day of gestation. The doses of T3 and T4 were biologically equivalent for the dams, as assessed from maternal plasma and tissue T3, and plasma TSH levels. MMI blocked the fetal thyroid; T4 and T3 levels were low in all fetal tissues, and fetal plasma TSH was high. Maternal infusion with T4 mitigated both T4 and T3 deficiency in all fetal tissues, the brain included, and decreased fetal plasma TSH. In contrast, infusion of T3 normalized fetal plasma T3 and increased the T3 levels in several tissues, but not in the brain. Neither did it decrease the high fetal plasma TSH levels. The results show that when the fetus is hypothyroid, T3 crosses the rat placenta at the end of gestation, but does not affect all tissues to the same degree. In contrast to the effects of maternal T4, maternal T3 does not alleviate the T3 deficiency of the brain or, presumably, of the thyrotrope. Thus, end-points of thyroid hormone action related to TSH release should not be used to measure transfer of maternal T3 to the fetal compartment. Moreover, T4 should be given, and not T3 to protect the hypothyroid fetal brain.

3,3',5'-Triiodothyronine inhibits ontogenetic development of iodothyronine-5'-deiodinase in the liver of the neonatal mouse

To elucidate the effect of rT3 on iodothyronine-5'-deiodinating activity (I-5'-DA) in the liver of neonatal mice, rT3 was injected sc on the 5-8th day after birth and I-5'-DA in the liver was determined. A single injection of rT3 (0.01-1 microgram/g) inhibited the ontogenetically developing I-5'-DA in a dose- and time-dependent manner. The inhibitory effect was reversible and specific for I-5'-DA. Lineweaver-Burk analysis revealed that the time- and dose-dependent decrease in the enzyme activity was due to a decrease in Vmax with no alteration in Km values (5 x 10(-8) mol/l). The maximal inhibitory effect was observed at a dose of 1 microgram rT3/g, whereas the inhibitory effect was diminished at greater doses (4-10 micrograms/g), probably owing to a contamination with T4 of the rT3 preparation administered. Furthermore, consistent with our previous in vitro findings, rT3 inhibited the I-5'-DA induced by T3 in the liver of neonatal mice. These findings suggest that rT3 inhibited I-5'-DA in the liver of neonatal mice by decreasing the amount of enzyme available to the substrate and that rT3 also elicited an antagonistic effect against T3 in the induction of I-5'-DA in vivo.

Effects of variation of the tri-iodothyronine/reverse triiodothyronine ratio in vivo on the metabolic characteristics of subsequently isolated hepatocytes

Reverse tri-iodothyronine (3,3',5'-tri-iodothyronine, rT3), a major product of the peripheral monodeiodination of thyroxine, was administered subcutaneously to fed rats at a dose of 100 micrograms/100 g body weight for 2 consecutive days. This dose induced a 17-fold increase in plasma rT3 (from 0.05 +/- SEM 0.01 to 0.85 +/- 0.11 ng/ml, P less than 0.001) whilst the plasma T3 concentration was decreased to half of the control value (0.40 +/- 0.03 to 0.20 +/- 0.02 ng/ml, P less than 0.01). As a result of these changes the T3/rT3 ratio was therefore decreased from 8.0 +/- 1.6 to 0.23 +/- 0.03 (P less than 0.001). Hepatocytes prepared from control or rT3-treated rats were incubated with [1-14C]oleate and the rates of 14CO2 release and glucose production were estimated. Despite the changes in ratio of T3 to rT3 observed in vivo, rates of 14CO2 release and glucose production rate from hepatocytes subsequently isolated were unchanged.

The bioavailability of thyroxine and 3,5,3'-triiodothyronine in normal subjects and in hyper- and hypothyroid patients

A new method for the estimation of the bioavailability of thyroxine (T4) and 3,5,3'-triiodothyronine (T3) is described based on gel separation followed by antibody extraction of labelled T4 and T3 from serum, and using the area under the curve of disappearance of the tracer (AUC) for the calculations. The peak serum concentrations of radioactive labelled T4 and T3 were reached approximately 90 min after oral administration of both tracers. The relative difference of duplicate estimations was below 10% (n = 3). The bioavailability of T4 in 6 euthyroid controls was in median 65% (range 64-75%), and it was significantly increased both in hyperthyroidism (88% (75-99%), n = 6, P less than 0.01) and hypothyroidism (84% (67-100%), n = 6, P less than 0.02). The bioavailability of T3 in 6 euthyroid controls was in median 78% (69-99%) and significantly greater than that of T4 (P less than 0.02). The bioavailability was unaffected by hyperthyroidism (79% (61-98%), n = 9) and hypothyroidism (77% (66-97%), n = 7). No significant difference between T4 and T3 bioavailabilities was found in hyper- or hypothyroidism. The clinical implication of the present study is that the bioavailability of T4 and T3 is almost identical and approximately 80% in patients with severe hypothyroidism.

Correlation of reverse-T3 and 3,3'-T2 (T2') plasma concentrations under physiological and experimental conditions in man

T2' plasma levels are measured under different conditions and correlated to the repective rT3 concentrations. Specific RIAs for T2' and rT3 are used. Pharmacological doses of T3 cause an increase of plasma T2'; if T3 or T4 doses are administered to an athyroid patient which cause a similar level of plasma T3 the increase of T2' is much larger during T4 treatment. Cord blood levels of T2' are 2--3-fold higher than in normal adults whereas rT3 concentrations are about 10 times higher than normal. After birth rT3 and T2' levels decrease in about a parallel manner. After a bolus iv injection of 500 microgram rT3, T2' starts to increase as early as 2 min after injection. PTU in therapeutic doses causes a rapid increase of plasma rT3 with a maximum 4 h after ingestion. A dose of 150 mg PTU causes a maximum of about 100% above baseline. T2' also increases but to a lesser degree (about 50% above baseline). We conclude that rT3 is a most important precursor of T2' whereas T3 contributes only to a minor degree to the total T2' production under physiological conditions.