Effects of lithium on thyroid hormone metabolism in rat frontal cortex.
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Animals↗
Biomedical subjects
H Meinhold
Publications and source records attributed to H Meinhold.
Subchronic administration of fluoxetine to rats affects triiodothyronine production and deiodination in regions of the cortex and in the limbic forebrain.
The effects of subchronic administration of the antidepressant fluoxetine (15 mg/kg i.p., 14 days) on thyroid hormone metabolism were investigated in 11 regions of the CNS and three peripheral tissues in the rat. Fluoxetine significantly enhanced the activity of the 5'II-deiodinase isoenzyme (5'D-II), which catalyzes the deiodination of the inactive prohormone thyroxine (T4) to the active compound triiodothyronine (T3) in areas of the cortex, the limbic forebrain and the striatum. The activity of the 5D-III deiodinase isoenzyme (5D-III), which catalyzes the further deiodination of T3 to the inactive metabolite 3,3'-T2, was inhibited in the first two of these areas. The areas affected were roughly the same as those with the highest density of 5-HT2 receptors in rat brain. Theoretically, the enhancement 5'D-II activity, together with a concomitant decrease in 5D-III activity, should lead to a rise in T3 concentrations. Whether or not these effects are involved in the as yet unknown mechanism of action of this antidepressant compound is discussed.
Animals↗
Carbamazepine affects triiodothyronine production and metabolization in rat hippocampus.
The effects of subchronic administration of carbamazepine on thyroid hormone metabolism were investigated in the hippocampus in adult male rats at two different measuring times (4 a.m. and 8 p.m.). Carbamazepine enhanced the activity of 5'II-deiodinase, which catalyzes the deiodination of the prohormone T4 to the active compound T3, at 8 p.m., but not at 4 a.m. The activity of 5III-deiodinase, which catalyzes the further deiodination of the active hormone T3 to its metabolite 3,3'T2, was inhibited at 4 a.m. but not at 8 p.m. These effects of carbamazepine on intracellular thyroid hormone metabolism in the hippocampus should theoretically lead to a rise in T3 production. It remains to be investigated whether they are somehow involved in the as yet unknown mechanisms underlying the anticonvulsant/mood-stabilizing effects of carbamazepine.
Animals↗
Interleukin-2 receptor--targeted therapy by monoclonal antibodies in the rat corneal graft.
A possible selective therapeutic approach to corneal graft rejection will aim at IL-2 receptor-bearing antigen-activated T-lymphocytes with monoclonal anti IL-2R antibodies. In a rat penetrating keratoplasty model (Lewis x Lewis-BN) comparing to controls (median, 8 days), a significant delay of the allograft reaction was achieved by applying a therapeutic dose (15 mg/kg bw) of cyclosporin A (median, 18 days; p < 0.01), an intraperitoneal (1.0 mg/kg bw) (median, 13.5 days; p < 0.05) or a subconjunctival injection of IL-2R mab (0.5 mg/kg bw ART-18) (median, 16 days; p < 0.01) with low-dose Cyclosporin A (1.5 mg/kg bw). In pharmacokinetic experiments, the corneal radioactivity 24 h after intraperitoneal injection of 125I-labeled ART-18 was < 1% (p < 0.01) of the values obtained by subconjunctival injection, whereas the serum radioactivity values (p > 0.05) were in the same range. The above results suggest that the onset of an allograft reaction in perforating keratoplasty seems to depend on the locally achievable antibody concentration and can be delayed with a high level of IL-2 R mab present in the immediate surrounding of the foreign antigen-expressing cells.
Animals↗
Hypothalamic-pituitary-thyroid axis in chronic alcoholism. II. Deiodinase activities and thyroid hormone concentrations in brain and peripheral tissues of rats chronically exposed to ethanol.
Thyroxine (T4), triiodothyronine (T3) concentrations, and the activities of the three deiodinase isoenzymes were measured in different brain regions and peripheral tissues of rats. According to an animal model of alcohol addiction, "behaviorally" dependent rats having lost control over their intake of ethanol were compared with alcohol-naive controls and ethanol-experienced, but "controlled" consumers. The two kinds of alcohol-experienced rats were investigated either 24 hr or 3 months after ethanol withdrawal. The results of these four groups were compared with those of an ethanol-naive control group. During withdrawal, the activities of type II 5'-deiodinase (which catalyzes deiodination of T4 and T3 in the CNS) in both the "behaviorally dependent" rats and the "controlled drinkers" were significantly lower than in the alcohol-naive controls in the frontal cortex, parieto-occipital cortex, hippocampus, and striatum, but not in the cerebellum or pituitary. Probably as a result, the tissue concentrations of T4 were higher in areas of the CNS in the groups exposed to alcohol. However, the T3 concentrations were normal. No relevant differences were seen between the activities of type III 5-deiodinase (which catalyzes the further deiodination of T3) observed in these groups. After 3 months of abstinence, the type II 5'-deiodinase activities had almost returned to normal in both "controlled drinkers" and "behaviorally dependent" animals, whereas type III 5-deiodinase activity was inhibited, possibly to maintain physiological concentrations of T3 during abstinence. Indeed, the tissue levels of T3 were normal in the areas of the CNS, and the T4 levels were still elevated. However, the liver concentrations of T3 and T4 were significantly lower in the "behaviourally dependent" animals than in the "controlled" drinkers after 3 months of abstinence, whereas no differences were found between the T4 and T3 concentrations in the areas of the CNS investigated in the two groups exposed to ethanol. These results suggest that chronic administration of ethanol affects intracellular thyroid hormone metabolism in both rat CNS and liver in the highly complex manner. No direct evidence of ethanol-induced enhancement of tissue uptake or concentrations was obtained. However, taking into account the numerous similarities between the clinical picture of hyperthyroidism and the symptomatology of alcoholism, it may be hypothesized that ethanol may directly influence any step in the as yet unknown biochemical cascade of thyroid hormone function.
Alcoholism↗
Etiological grouping of permanent congenital hypothyroidism with a thyroid gland in situ.
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Congenital Hypothyroidism↗
The influence of desipramine on thyroid hormone metabolism in rat brain.
The effect of the antidepressant desipramine (DMI) on the activities of the three iodothyronine deiodinase isoenzymes involved in the central metabolism of thyroid hormones were investigated in 11 brain regions and 3 peripheral tissues in the rat. The investigations were carried out at three different times during the light/dark cycle: 5 A.M., 1 P.M. and 11 P.M. Interest is focused on changes in the two enzymes that catalyze: i) the 5'deiodination of T4 to the biologically active T3, i.e., type II 5'deiodinase (5'D-II), and ii) the 5 (or inner-ring) deiodination of T3 to the biologically inactive 3,3'T2, i.e., type III 5 deiodinase (5D-III). Fourteen days' treatment with 20 mg/kg DMI, but not with 5 mg/kg DMI, induced significant increases in 5'D-II in eight different areas of the CNS. The regions affected were identical to those that receive noradrenergic input from the locus coeruleus. Even control animals showed a circadian rhythm of 5'D-II activity in some brain regions, and the effects of DMI also depended on the time of death within the 24-hr rhythm. 5D-III was not affected. Serum T4 were lower after administration of DMI, most probably because of enhanced tissue uptake of T4. This is in line with the corresponding finding in depressed patients, indicating that similar changes in both central and peripheral thyroid hormone metabolism may occur after antidepressant pharmacotherapy in both humans and rats. These data support the hypothesis that interactions with the CNS metabolism of the thyroid hormones may be involved in the mechanisms of action of DMI.
Animals↗
The influence of sleep deprivation on thyroid hormone metabolism in rat frontal cortex.
The effects of 24 h sleep deprivation (SD) on central thyroid hormone metabolism were investigated in rat frontal cortex. SD induced a significant rise in the activity of iodothyronine type II 5'-deiodinase (5'D-II), which catalyzes the conversion of thyroxine (T4) to triiodothyronine (T3) in the rat central nervous system (CNS). Tissue concentrations of T4 remained unchanged, whereas levels of T3 increased to more than 150% of the corresponding levels measured in control rats. Serum concentrations of T4 and T3 were also significantly enhanced by SD--an effect that has previously been described in depressed patients having undergone the same procedure. These results suggest that SD can dramatically increase T3 concentrations (and possibly function) in rat CNS. Whether or not these findings are of relevance in regard to the well-known antidepressant effect of SD in psychiatric patients with major depressive disorders remains to be established.
Animals↗
Effects of selenium and iodine deficiency on type I, type II and type III iodothyronine deiodinases and circulating thyroid hormones in the rat.
The effects of nutritional selenium (Se) deficiency over a period of three generations and of a combined selenium and iodine deficiency on hepatic and cerebrocortical iodothyronine deiodinases and on circulating thyroid hormone levels were examined in the rat. Se deficiency strongly decreased hepatic type I iodothyronine 5'- and 5-deiodinase to 6-13% of that in controls. Iodine depletion had only a marginal decreasing effect on the type I activity. Cerebrocortical type II 5'-deiodinase was decreased in Se-deficient, iodine-replete rats. Its 5-6-fold elevation in iodine-deficient rats was not reversed by additional selenium deficiency. Cortex type III 5-deiodinase was modestly decreased in all groups with insufficient trace element supply. Long-term Se deficiency has only limited effects on serum T4 and T3 levels. Two months of iodine deficiency decreased serum T4 to less than 10% of that in controls, but did not significantly affect serum T3 levels. The strong decrease of hepatic outer- and inner-ring deiodination of T4 in Se deficiency obviously reflects the reduced tissue concentration of the type I deiodinase which was recently identified as a selenoenzyme. The maintenance of increased cerebrocortical type II deiodinase in iodine-depleted animals irrespective of adequate or deficient selenium supply suggests that the type II isoenzyme does not contain selenium in its catalytic site. Further studies are necessary to clarify whether the weak, but repeatedly confirmed decrease of cortex type III deiodinase is the direct effect of Se deficiency or the indirect consequence of the multilevel change in thyroid hormone metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Increased plasma T4-levels in children with low selenium state due to reduced type I iodothyronine 5'deiodinase activity?
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Adolescent↗
Hemodynamic responses to noxious stimuli in brain-dead organ donors.
The case report presents evidence for the spinal origin of the marked hypertensive responses to noxious stimuli that may occur in organ donors who fulfill the commonly accepted criteria of brain death. Cardiovascular spinal reflex activity does not invalidate these criteria. For the first time, the catecholamine plasma concentrations have been determined during spinal pressor reflex activity. Circulating epinephrine increased more markedly than norepinephrine in both cases, rising to 4.7 and 44 times the baseline concentration respectively. The relation between plasma norepinephrine and epinephrine suggests involvement of the adrenal medulla in the reflex arc. The literature on spinal hemodynamic reflexes is reviewed.
Adult↗
Type I iodothyronine deiodinase activity after high selenium intake, and relations between selenium and iodine metabolism in rats.
Type I iodothyronine deiodinase (I-D), which catalyzes the production of the thyroid hormone 3,3',5-triiodothyronine from thyroxine, has recently been identified as a selenoenzyme. It is therefore of interest to investigate the relationships between selenium and iodine metabolism. In the livers of Se-deficient rats I-D activity was inhibited; the production of 3,3',5-triiodothyronine and 3,3'-diiodothyronine from added thyroxine was decreased by greater than 95% relative to Se-adequate controls. The hepatic I-D activity was also reduced in rats fed a diet with a low iodine concentration. Unaltered glutathione peroxidase activities in liver and plasma of these rats suggest, however, that with normal Se intake this metabolic pathway of Se is not affected by iodine depletion. When rats were administered 75Se-labeled selenium at levels equal to the amounts ingested from diets with Se concentrations of 0.3 or 2 mg Se/kg, greater Se concentrations were found in the thyroid and liver of the animals receiving the higher dosage. The thyroidal 3,3',5-triiodothyronine and thyroxine concentrations, however, were comparable in rats fed diets with 0.3 mg Se/kg diet as selenite and 2 mg Se/kg as selenite or L-selenomethionine. The measurement of the hepatic I-D and glutathione peroxidase activities in these animals showed that excessive Se supply does not elevate the activities of the two enzymes but might even have the opposite effect. At high Se intake tissue Se concentration cannot therefore be used as indicator of the selenoenzyme activities.
Administration, Oral↗
Acute endocrine failure after brain death?
After brain death, 32 potential organ donors were studied to determine serum and plasma concentrations of hypothalamic-pituitary hormones, thyroid hormones, and cortisol over a period of up to 80 hr. Diagnosis of brain death was established either on the basis of clinical criteria (n = 16) or by angiography (n = 16). While 78% of the organ donors developed diabetes insipidus, none of the circulating hormones of the anterior pituitary gland showed a progressive decline in concentration according to their plasma half-lives. With the exception of arginine vasopressin (AVP), no hormone concentration was found to be subnormal due to the onset of brain death. The subnormal free triiodothyronine (FT3) values in 62% of cases (median FT3 of 2.2 pmol/L within the first 24 hr) and the cortisol concentration of 6.9 micrograms/dl correlate with the frequency of similar findings in patients with severe head injuries. While the adrenocorticotropic hormone (ACTH) concentrations of 10-53 pg/ml remained constant during the study period, thyroid-stimulating hormone (TSH) and human growth hormone (hGH) concentrations showed a 12- and 35-fold increase from baseline values after 30-40 hr. These results suggest that, despite the now generally accepted criteria of brain death, there is still some residual function, and thus also perfusion of the hypothalamic-pituitary neuroendocrine system. This residual function appears to be sufficient to maintain hormonal plasma levels at least in the low reference range in most donors. Hormonal depletion in organ donors subsequent to brain death, as suggested repeatedly in the literature, could not be confirmed. The analysis of serum or plasma concentration patterns of a number of hormonal parameters following brain death does not support the rationale for a routine replacement therapy of total triiodothyronine (TT3) or cortisol to maintain endocrine homeostasis prior to organ harvest. However, dexamethasone therapy may be followed by suppression of the adrenal cortex of the organ donor. In these cases, cortisol substitution may be indicated.
Adrenocorticotropic Hormone↗
Effects of selenium and iodine deficiency on iodothyronine deiodinases in brain, thyroid and peripheral tissue.
Long term nutritional selenium (Se) deficiency had only marginal effects on the thyroid T4 and T3 content and on the activity of the selenoenzyme type I deiodinase (5'D-I) in the thyroid gland. These findings reveal a remarkable resistance of the thyroid to Se-deficiency which may substantially contribute to the observed maintenance of T4 and T3 levels in circulating blood. In contrast to its maintained thyroidal activity, 5'D-I in peripheral tissues like liver and kidney was strongly decreased by Se-deficiency. The observed decrease of type II deiodinase (5'D-II) in the cerebral cortex of Se-deficient rats was obviously caused by the suppressing regulatory effect of elevated cortex T4 concentrations. The severalfold 5'D-II enhancement in iodine depleted animals was not abolished by additional Se-deficiency, suggesting that brain type II deiodinase is not a selenoenzyme. The role of selenium for cortex type III 5-deiodinase, which was moderately decreased in selenium as well as iodine-deficient rats, awaits definite evaluation by further studies. The different responsiveness to thyroidal and hepatic 5'D-I to Se restriction is further evidence for priorities in the selenium supply to different tissues.
Animals↗
Thyroid hormones and depressive illness: implications for clinical and basic research.
It has been well-known for at least 100 years that both hypo- and hyperthyroidism may cause almost any psychiatric symptom, depending on the severity of the illness. No thyroid disorder, however, induces symptoms that are specific for a psychiatric disorder. Laboratory tests show depressed patients to be euthyroid. Any abnormalities that have been found, such as slightly elevated T4 levels or decreased T3 or TSH concentrations, have frequently failed to be replicated and do not fit any endocrinological diagnosis. They could reflect either "intervening factors" such as stress, methodological problems or a disturbance of central thyroid hormone metabolism. All antidepressant therapies (antidepressant drugs, carbamazepine, lithium, electroconvulsive therapy and sleep deprivation) have a marked influence on peripheral thyroid hormone levels. In particular, decreases in serum T4 and rT3 levels are often correlated to antidepressant response, suggesting that an effect on central thyroid hormone metabolism is involved in the as yet unknown mechanism of action of these therapies. Indeed, animal studies have shown that antidepressants do affect deiodinase activities and T3 and T4 concentrations in rat brain. However, the effects are highly area specific and dependent on the drug administered and the time of day at which the investigation was conducted. Although the mechanism of thyroid hormone action on CSF signal transduction is as yet unknown, effects on "general CNS functions" such as second messengers, G-proteins or calcium homeostasis seem more likely than specific effects on the different receptor systems.
Animals↗
Elevated serum diiodotyrosine (DIT) in severe infections and sepsis: DIT, a possible new marker of leukocyte activity.
Ether link cleavage (ELC) of T4 yielding diiodotyrosine (DIT) has recently been shown in vitro to be the major pathway of T4 metabolism in phagocytosing leukocytes. To evaluate this pathway in vivo and the possible clinical relevance of DIT measurements in diseases with increased leukocyte activity, radioimmunological studies on serum levels of DIT and other thyroid parameters were performed in 125 critically ill patients classified into 3 groups with bacterial infections according to the severity of infection and 1 group without infections. While the pattern of iodothyronine and TSH levels typical for severe nonthyroidal disorders, i.e. decreased total T3 and elevated rT3, normal or decreased total T4 and TSH, and normal free T4, was found in all four groups of intensive care patients studied, elevated serum DIT was observed only in those patients whose clinical course was complicated by severe bacterial infections. Serial measurements revealed a close temporal connection between the infection phase and increased DIT levels. Median values and 16th to 84th percentile ranges (in parentheses) of serum DIT (normal range, 0.02-0.55 nmol/L) were as follows: sepsis, 1.38 (0.32-5.14); severe nonsystemic infections such as peritonitis and abscesses, 3.84 (0.24-17.2); moderate infections such as pneumonia and tracheobronchitis, 0.44 (0.18-1.16); and critical illness without infections, 0.14 (0.08-0.30) nmol/L. These elevations of circulating DIT could neither be correlated with changes in renal function nor attributed to drug effects. The results of the present study do not allow any definitive conclusions to be made about the mechanisms underlying the phenomenon of increased serum DIT levels in infections. Apart from this open question, DIT appears to be a relatively specific serum parameter for the presence and course of severe bacterial inflammations. Its measurement could provide useful clinical information, particularly for monitoring the time course of deep-seated infections.
Bacterial Infections↗
Identification of type I iodothyronine 5'-deiodinase as a selenoenzyme.
A 27.8 kDa membrane selenoprotein was previously identified in rat thyroid, liver and kidney, the tissues with the highest activities of type I iodothyronine 5'-deiodinase. This membrane enzyme catalyzes the deiodination of L-thyroxine to the biologically active thyroid hormone 3,3',5-triiodothyronine. A decrease in the activity of this enzyme, observed here in the liver of selenium-deficient rats, was found to be due to the absence of a selenium-dependent membrane-bound component. By chemical and enzymatic fragmentation of the 75Se-labeled selenoprotein and of the 27 kDa substrate binding type I 5'-deiodinase subunit, affinity-labeled with N-bromoacetyl-[125I]L-thyroxine, and comparison of the tracer distribution in the peptide fragments the identity of the two proteins was shown. The data indicate that the deiodinase subunit contains one selenium atom per molecule and suggest that a highly reactive selenocysteine is the residue essential for the catalysis of 5'-deiodination. From the results it can be concluded that type I iodothyronine 5'-deiodinase is a selenoenzyme.
Animals↗
Neuroendocrinological investigations during sleep deprivation in depression. I. Early morning levels of thyrotropin, TH, cortisol, prolactin, LH, FSH, estradiol, and testosterone.
Measurements of 12 hormones were conducted in patients with major depressive disorder at 8 AM on the morning before and at 8 AM on the morning after total sleep deprivation (SD). Thyrotropin (TSH), thyroxine (T4), triiodothyronine (T3), and free T3 (fT3) were measured in 50 patients, free T4 in 39 patients, reverse T3, cortisol, prolactin, luteinizing hormone, and follicle-stimulating hormone in 21, estradiol in 20 (women), and testosterone in 14 (men). After SD, there was a significant rise in TSH, T4, T3, and fT3 concentrations and a significant fall in testosterone levels. The increases in TSH levels were significantly correlated to clinical response. Responders to SD had higher T4, fT4, rT3, and testosterone concentrations before SD. Neither age, gender, polarity, nor antidepressant medication had a clearly significant effect on the response to SD.
Adult↗