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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of starvation on thyroid hormone metabolism was studied in monkey hepatocarcinoma monolayer cultures. Nonphenolic ring monodeiodination of thyroxine, 3, 5, 3'-triiodothyronine and 3, 3'-diiodothyronine was accelerated. Since phenolic ring deiodination of 3, 3',5'-triiodothyronine (reverse T3) was unaffected, this metabolite accumulated in the medium during thyroxine metabolism. This suggests that increased serum reverse T3 in malnourished humans may be caused by enhanced deiodination of thyroxine rather than decreased rT3 catabolism.
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PMID:Thyroxine inactivation by starvation in cultured hepatocarcinoma cells, Formation of reverse triiodothyronine. 10 81

Although the molecular basis of thyroid hormone action remains obscure, a growing body of evidence has suggested that triiodothyronine (T3) action is initiated at a set of specific nuclear receptor sites. The physiologic significance of these T3-binding sites is supported by four lines of evidence: 1) the high-affinity, limited-capacity binding of T3; 2) the relationship between binding affinity of thyroid hormone analogs and hormonal potency; 3) the correlation of concentration of nuclear receptor and physiologic response in various tissues; 4) the relationship between receptor occupancy and physiologic response. While the levels of hepatic nuclear receptor do not change in response to T3, recent evidence indicates receptor concentration is markedly reduced by partial hepatectomy, starvation, or administration of glucagon. This reduction results in a decrease in the response of malic enzyme to T3, but leaves the response of alpha-glycerol phosphate dehydrogenase unimpaired. Thus, specific control of thyroid responses by modulating receptor concentration may occur. Occupancy of hepatic receptors by T3 is associated with increases in both the rate of formation and steady-state concentration of poly(A)-containing mRNA. The values of these two parameters in the euthyroid rat liver were approximately 60--80% greater than values in hypothyroid animals. Analyses of the sequence and frequency complexity of poly(A)-containing mRNA from euthyroid and hypothyroid rats revealed no major changes in either the qualitative or quantitative distribution of mRNA sequences. Although it is recognized that the levels of certain specific species of mRNA (ie, alpha 2u-globulin) are altered as a result of thyroid hormone action, these data strongly indicate a concomitant generalized increase in the production of all major classes of mRNA.
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PMID:Interaction of thyroid hormones with target tissues: effects of hepatic mRNA population. 23 83

To investigate further the alterations in pituitary-thyroid function seen during starvation, we have measured basal and TRH-stimulated serum levels of thyrotropin (TSH), prolactin (PRL), growth hormone, thyroxine (T4), triiodothyronine (T3), free T4, free T3, and reverse T3 during prolonged fasting in seven obese men. Fasting was associated with a significant decrease in serum (4, (3, and free T3, while there was an increase in serum reverse T3; these values tended to return toward pre-fast levels as the fast continued beyond 3 weeks. No significant changes were seen in basal serum TSH, PRL, growth hormone, or free T4. Although the TSH response to TRH was diminished during fasting, PRL, T4, and T3 responses were unchanged. In addition to transient alterations in the peripheral metabolism of T4, these findings suggest that alterations in the thyroid hormone binding capacity of serum carrier proteins may occur during fasting. The blunted TSH response to TRH despite reduction of serum T3 concentration suggests that subtle alterations in hypothalamic-pituitary function may also occur.
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PMID:Alterations in basal and TRH-stimulated serum levels of thyrotropin, prolactin, and thyroid hormones in starved obese men. 41 Aug 22

The effect of moderate bicycle exercise (3.5 h) on peripheral thyroid hormone metabolism was studied under two conditions (with and without glucose infusion) in four normal males. Serum T3, rT3, total protein, plasma glucose, and FFA were determined. Exercise induced an increase in rT3 from 29 to 40 ng/dl (P less than 0.01), a decrease in T3 from 154 to 147 ng/dl (P less than 0.01), and an increase in T4 from 7.1 to 7.5 micrograms/dl (P less than 0.05). When glucose was infused during exercise, the changes in rT3 were blunted (P less than 0.01) and the changes in T3 and T4 were diminished. During exercise, rT3 correlated with FFA (r = 0.95) and plasma glucose (r = -0.87). When glucose was infused during exercise, these correlations decreased (r = 0.81 and -0.56, respectively). Since moderate, prolonged exercise induces a state of early or acute starvation it is concluded that the changes in peripheral thyroid hormone metabolism reported here are similar to those found in starvation. The temporal changes of rT3, FFA, and plasma glucose during exercise suggest a relationship between thyroid hormone metabolism and the uptake and utilization of FFA and glucose or the mixture of these body fuels.
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PMID:Changes in serum concentrations of 3,3',5'-triiodothyronine and 3,5,3'-triiodothyronine during prolonged moderate exercise. 45 43

Patients with anorexia nervosa can demonstrate clinical and/or laboratory findings suggestive of reduced thyroid hormone secretion. In this study, the thyroxine (T4) and triiodothyronine (T3) serum concentrations, and thyrotropin (TSH) response to intravenous administration of thyrotropin releasing hormone (TRH) were determined in 6 patients (aged 9 to 15 yr) with anorexia nervosa and the results compared to those found in a group of 15 normal subjects. The mean basal TSH concentration and mean maximum increase in TSH after TRH were comparable to those in the normal subjects. The mean T4 concentration (7.2 mug/100 ml) in the anorexia nerovsa group was slightly but significantly lower than in the normal group (9.5 mug/100 ml). Five of the 6 patients had serum T3 concentrations below the lower limits of normal and the mean T3 concentrations (49.7 ng/100 ml) was significantly lower than in the normal group (106 ng/100 ml). The extremely low serum levels of T3 in these patients with anorexia nervosa suggest that peripheral conversion of T4 to T3 is impaired during chronic starvation.
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PMID:Low serum triiodothyronine in patients with anorexia nervosa. 80 75

The acute effect of triiodothyronine (T3) on mobilization of fat and protein energy stores has been measured in five fasting, normal men. Fasting subjects were chosen for this study to amplify catabolic effects occurring during brief thyroid hormone treatment. Subjects were fasted for 72 hr on two occasions with admintration of T3, 150 mug every 12 hr, for 72 hr before and during the second fast. Plasma beta hydroxybutyrate, acetoacetate, and free fatty acid levels as well as ketone, creatine, and urea excretion were measured during control and T3 fasts. T3 enhances catabolism of protein stores as indicated by the doubling of urea excretion during the T3 fasts. Likewise, creatine excretion is increased six to ninefold during the T3 fasts. Catabolism of fat stores is enhanced during the T3 fasts as shown by increased plasma free fatty acid and ketone levels, and increased ketone excretion. Brief T3 treatment for 3 days augments the expected protein and fat catabolism of starvation without causing subjective changes of hyperthyroidism. Much of the catabolic expression of hyperthyroidism may simply reflect inadequate caloric intake to fuel energy requiring processes stimulated by thyroid hormone such as cell membrane sodium pumping and protein synthesis.
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PMID:Effect of thyroid hormone on metabolic adaptation to fasting. 116 32

We have studied the presence of the messenger RNA (mRNA) for the cytosolic enzyme, phosphoenolpyruvate carboxykinase (PEPCK), in rat lung by Northern blot hybridization to a complementary DNA (cDNA) probe. Lung from normal rats contained substantial amounts of this mRNA, although its relative concentration was approximately six times lower than in liver. Fasting produced an eightfold increase in the content of the enzyme mRNA in lung, which could be reverted to normal values by glucose refeeding. Induced diabetes also resulted in a sevenfold increase of the levels of PEPCK mRNA in lung. Dexamethasone, thyroid hormone, dibutyryl cyclic adenosine monophosphate (cAMP), histamine, and serotonin also induced important accumulations of the enzyme mRNA without affecting the concentration of beta-tubulin mRNA measured as reference. Thus, the PEPCK gene appears to be regulated in a similar manner in lung and liver. The results suggest that PEPCK may be involved in lung metabolism in starvation, diabetes, and other specific hormonal situations.
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PMID:Detection and hormonal regulation of the mRNA for cytosolic phosphoenolpyruvate carboxykinase in rat lung. 162

To elucidate the possible role of adrenergic mechanism in thyroid hormone metabolism during starvation, serum thyrotropin (TSH), thyroxine (T4), and 3,5,3'-triiodothyronine (T3) levels and conversion of T4 to T3 in perfused liver were investigated in fasting (60 h) and fed rats. Propranolol (0.5 mg/kg), yohimbine (0.3 mg/kg) or phentolamine (5.0 mg/kg) was subcutaneously injected to the rat every 12 h. Serum levels of TSH, T4, and T3 were significantly lower in fasting rats than in fed rats. Although propranolol, yohimbine, and phentolamine administration did not significantly alter circulating TSH, T4 and T3 levels in fed rats, phentolamine partly inhibited the starvation-induced reduction in circulating TSH, T4, and T3. Thyroxine uptake and T3 production in perfused liver were significantly lower in fasting rats than in fed rats. Phentolamine treatment did not alter the T4 uptake and T3 production in perfused liver of fasting rats. These results suggest that alpha-adrenergic mechanism may have some role in starvation-induced reduction in circulating T4 and T3, and that phentolamine partly inhibited this phenomenon probably through the inhibitory effect on reduction in circulating TSH during starvation.
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PMID:Possible role of adrenergic mechanism in starvation-induced reduction in circulating thyroxine and triiodothyronine in rats. 164 11

Serious nonthyroid illness and caloric deprivation, which so often accompany systemic illness, have diverse and still incompletely understood effects on thyroid hormone economy. We have discussed the pathophysiologic basis for the most common pattern of alterations in routine thyroid function tests: a decreased serum T3 concentration; normal or, in critically ill patients, a low total serum T4 level; and a normal free T4 concentration. Another, less frequent pattern (high total and free T4 with a normal serum T3) can be encountered transiently in the acutely ill medical or psychiatric patient. With the recent advent of sensitive assays for TSH and better methods for serum free T4, it is now possible to define more quickly and accurately the thyroid-metabolic status of most of these sick patients; the vast majority are euthyroid. Certain drugs confound the picture. The most important of these include dopamine and high-dose glucocorticoids, both of which suppress TSH secretion from the pituitary and may actually cause a state of central hypothyroidism. Other drugs have multiple effects on thyroid hormone indices (e.g., amiodarone). Knowledge of all of the ways in which systemic illness, starvation, and certain drugs may influence thyroid function tests is crucial in assessing the thyroid status of patients with serious nonthyroid disease.
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PMID:The effects of nonthyroid disease and drugs on thyroid function tests. 198 45

Thyroid hormones act at the transcriptional level in the induction of the important hepatic glucoregulatory enzyme PEP-carboxykinase and glucokinase (Fig. 1 and Fig. 2). They have no significant effect on the degradation of both enzymes, nor on the degradation of the specific mRNAs. A T3-receptor interaction is essential for their effect. Suggestions have been made for a thyroid hormone regulatory element in the promotor region of T3-dependent genes (for a review see [18]). Thyroid hormones probably do not determine the direction of the metabolic flux; however, they significantly enhance in a permissive way the transition from one state, e.g. starvation, to another, e.g. refeeding. And by enhancing significantly the activity of important regulatory enzymes, they enhance the flux of metabolites under different metabolic conditions, such as in starvation or after refeeding.
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PMID:Role of thyroid hormones in the regulation of hepatic glucokinase and phosphoenolpyruvate-carboxykinase gene expression during the starvation-refeeding transition. 208 92


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