Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.6.1.1 (adenylate cyclase)
19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aim of this study was to determine, with a rat thyroid fragment perifusion system, the short-term (20 min) effect of forskolin (FK), an adenylate cyclase activator, on T4 secretion, the effect of forskolin on T4 secretion stimulated by theophylline and TSH, and the role played by calcium in the forskolin effect. A dose-dependent effect on T4 secretion was obtained with forskolin, from 10(-8) to 10(-4) mol/l, with a maximal effect between 10(-6) and 10(-5) mol/l. The effect of forskolin was not increased by theophylline. The combined stimulation with forskolin and theophylline induced a T4 release which remained significantly lower than the effect of 22 or 65 mIU/ml TSH. Forskolin slightly increased the stimulating effect of 22 mIU/ml TSH but significantly decreased the effect of 65 mIU/ml TSH. A reduction in the buffer calcium concentration slightly decreased the effect of the forskolin and theophylline stimulations and the effect of the combined stimulation with forskolin and theophylline without suppressing completely the effect of these stimulations. This study demonstrates that 1) low concentrations of forskolin are able to induce a significant T4 release during short-term stimulations; 2) calcium is necessary in order to obtain a maximum effect of adenylate cyclase activation on T4 release; 3) the part of the thyroid hormone response to TSH which is mediated by adenylate cyclase activation is relatively small.
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PMID:Stimulating effect of forskolin on thyroxine secretion. Influence of calcium. 205 24

TSH, the major signalling factor for the thyroid follicles, controls thyrocyte function in concert with other modulators of cell growth, differentiation and structural organization of the follicular-endothelial network. Most of the TSH effects are mediated by TSH binding to the TSH receptor which stimulates adenylate cyclase catalyzed cAMP production. TSH is involved in the regulation of thyroidal uptake of small molecules and nutrients, intracellular transport of thyrocyte specific proteins, and in most of the steps of thyroid hormone synthesis, storage and release. These cellular events require the fine tuned regulation of metabolic reactions, morphological differentiation and cell proliferation. Thyrocytes also express a highly active Type I iodothyronine 5' deiodinase which is controlled by TSH stimulated cAMP production. The thyrocyte specific 5' deiodinase isozyme has marked influence on the amount of T3 secreted by the thyroid. This 5' deiodinase isozyme shows most of the characteristics of the type I 5' deiodinase found in liver and kidney and is also blocked by PTU, other 5' deiodinase inhibitors, and iodinated X-ray contrast agents such as iopanoic acid, which are occasionally used in thyrotoxicosis to inhibit thyroidal T3-production by this enzyme. In contrast to the liver and kidney type I 5' deiodinase T4 and T3 are not able to induce this enzyme in thyrocytes. However, TSH stimulated cAMP production increases the thyroidal isozyme activity in contrast to the liver and kidney enzyme. This review summarizes the data on the various experimental models used up to date to characterize the thyroidal type I 5' deiodinase in various species including man.
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PMID:Thyrotropin (TSH) action on thyroid hormone deiodination and secretion: one aspect of thyrotropin regulation of thyroid cell biology. 221 Jun 28

We have used cultured 3T3-L1 adipocytes to assess direct effects of T3 on beta-adrenergic-mediated regulation of lipolysis and adenylate cyclase and phosphodiesterase activities. Differentiated 3T3-L1 adipocytes were maintained under four conditions: in the presence of medium containing serum from a hypothyroid calf (hypothyroid medium), hypothyroid medium supplemented with T3 (T3-supplemented hypothyroid medium), medium with serum from a normal calf (control medium), and control medium supplemented with excess T3 (hyperthyroid medium). Compared to the two control groups, i.e. cells maintained in control medium or T3-supplemented hypothyroid medium, cells maintained in hypothyroid medium exhibited lower basal rates of lipolysis and lower sensitivity to isoproterenol. Hyperthyroid cells exhibited higher basal rates of lipolysis and higher sensitivity to isoproterenol. In the presence of maximally effective concentrations of isoproterenol, rates of lipolysis were similar in the four groups. Similarly, basal cAMP content and cAMP accumulation in the presence of isoproterenol were reduced in hypothyroid and increased in hyperthyroid adipocytes compared to those adipocytes maintained in control or T3-supplemented hypothyroid medium. Basal adenylate cyclase activity was similar in the four groups. Sensitivity to isoproterenol and maximal isoproterenol-stimulated cyclase activity were diminished in membrane preparations from hypothyroid adipocytes and increased in preparations from hyperthyroid adipocytes. Cyclase activity in the presence of NaF, however, was similar in preparations from cells maintained in hypothyroid, T3-supplemental hypothyroid, or control medium. NaF-stimulated activity was increased in preparations from hyperthyroid adipocytes. Thyroid status did not affect beta-receptor number of affinity for iodohydroxybenzylpindolol. Compared to control cells or cells maintained in T3-supplemented hypothyroid medium, both soluble and particulate cAMP phosphodiesterase activities were increased in hypothyroid cells and decreased in hyperthyroid cells. These results indicated that in 3T3-L1 adipocytes, some of the effects of thyroid hormone on cAMP content and lipolysis can be explained by alterations in both production and degradation of cAMP.
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PMID:Effects of thyroid hormone on regulation of lipolysis and adenosine 3',5'-monophosphate metabolism in 3T3-L1 adipocytes. 241 Feb 43

Rat GH gene expression is known to be stimulated by several factors, including thyroid hormone and GRF. This effect of GRF appears to be mediated by cAMP resulting from activation of adenylate cyclase by the peptide. The elements of the rat GH gene important for thyroid hormone stimulation and cell-specific expression have been previously mapped using gene transfection techniques. Cell-specific expression of the gene is mediated by two cell-specific elements located from -137 to -107 and from -95 to -65. Sequences mediating thyroid hormone stimulation are thought to be located between -208 and -160. In this study, using three different methods to elevate cAMP levels in cells [forskolin, a direct activator of the adenylate cyclase catalytic subunit; 8-(4-chlorophenylthio)cAMP, a nonmetabolizable cAMP analog; and isobutylmethylxanthine, a phosphodiesterase inhibitor], we show that 5'-flanking DNA of the rat GH gene can mediate stimulation by cAMP (10- to 20-fold). The cAMP-responsive region was mapped to sequences between -104 and +11, which contains the proximal cell-specific element (-95/-65) important for cell-specific expression. Either the -97/-65 or the -104/-47 region of the gene, cloned upstream of a heterologous promoter, conferred only minimal or no activation by cAMP. This suggests that these sequences are not the direct target of cAMP action or that they are insufficient alone to mediate the cAMP response. The cAMP regulatory element (TGACGTCA) is not found between - 104 and +11, and cAMP activation does not appear to act via putative AP-2 elements, since phorbol esters did not stimulate expression.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Identification of an adenosine 3',5'-monophosphate (cAMP)-responsive region in the rat growth hormone gene: evidence for independent and synergistic effects of cAMP and thyroid hormone on gene expression. 247 28

Thyroid abnormalities may develop during chronic lithium therapy for affective disorders. Lithium, like iodide, inhibits TSH stimulation of adenylate cyclase and thyroid hormone release. The present study examined the effect of lithium on stimulation of intrathyroidal intermediary metabolism by several agonists. LiCl (5 mmol/l) did not inhibit basal cAMP, glucose oxidation or 32P incorporation into phospholipids in dog thyroid slices. Although LiCl inhibited TSH stimulation of cAMP, it did not abolish the hormone's effect on cAMP-dependent protein kinase. The stimulation of iodide organification, glucose oxidation or 32P incorporation into phospholipids by TSH, carbachol and phorbol esters was not inhibited by lithium. This is in contrast to the effects of iodide, which inhibited stimulation of glucose oxidation and 32P incorporation into phospholipids by various agonists. Thus, although both lithium and iodide inhibited TSH-stimulated cAMP formation, they act differently on intrathyroidal intermediary metabolism.
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PMID:Effects of lithium on stimulated metabolic parameters in dog thyroid slices. 255 92

The enzyme thyroid peroxidase (TPO) plays a central role in thyroid hormone synthesis and is the target for the autoimmune attack in lymphocytic thyroiditis. We have examined the activation of the TPO gene in cultured human thyrocytes using slot-blot hybridization with a synthetic 40 mer oligonucleotide probe derived from the nucleotide sequence of the human TPO gene. The oligonucleotide probe was shown by Northern blotting to hybridize specifically to an approximately 3 kb RNA species from thyroid tissue of patients with Graves' disease, but not to RNA preparations from human or bovine retinal tissue, providing compelling evidence for the specificity of the probe for TPO mRNA. Addition of TSH (10 mU/ml) to primary thyroid cultures for 4 h led to increased TPO mRNA levels which were maximal after 48 h and significantly higher than basal even after 7 days of co-culture. Activation of TPO mRNA by TSH showed dose dependency over a wide range (0.01-100 mU/ml), with a maximal effect at 10 mU TSH/ml in cells cultured for a period of 72 h. Comparison of TPO mRNA levels with the accumulation of thyroglobulin mRNA levels following stimulation by TSH indicated that the induction of the gene encoding thyroglobulin precedes transcription of the TPO gene. The adenylate cyclase activator forskolin (1-100 microM) mimicked TSH in increasing TPO mRNA levels whilst, in contrast, the phorbol ester 12-O-tetradecanoyl phorbol 13-acetate (TPA; 0.01-1 microM) led to levels of TPO mRNA that were lower than basal. Thus TSH induces a specific dose-dependent activation of TPO mRNA which is mimicked by agents which increase cyclic AMP. In contrast, TPA-induced activation of protein kinase C inhibits this response.
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PMID:Activation of the thyroid peroxidase gene in human thyroid cells: effect of thyrotrophin, forskolin and phorbol ester. 274 42

Several thyroid hormone binding inhibitors have been described in nonthyroid illness. One of the major inhibitors, oleic acid, is present in excess amounts in sera of patients with nonthyroid illness. In this study, we demonstrated that oleic acid inhibited the cAMP accumulation of thyroid plasma membrane activated by thyrotropin at 50 mumol/l and higher concentrations. In the presence of albumin, oleic acid significantly inhibited the cAMP accumulation of plasma membrane activated by thyrotropin at 2.4 mmol/l (P less than 0.01 when the albumin concentration was 40 g/l and pH was 7.4; P less than 0.001 when the albumin concentration was 20 g/l and pH was 7.2). These findings suggest that in nonthyroid illness, especially at a low albumin concentration and low blood pH, a high oleic acid concentration may influence the thyroid function directly in addition to inhibiting the thyroid hormone binding to serum protein. Oleic acid also could inhibit 5'-guanylylimidodiphosphate- and forskolin-induced cAMP production in thyroid plasma membranes. Therefore, the inhibiting effect of oleic acid may be through the action of oleic acid on the catalytic unit of the hormone-sensitive adenylate cyclase system.
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PMID:The influence of oleic acid on cAMP accumulation of thyroid plasma membrane activated by thyrotropin. 283 81

Subcutaneous administration of bovine (b) TSH (up to 10 IU) to 8-week-old male guinea pigs was followed by a transient elevation in serum thyroid hormone levels (T4 and T3) and an increase in thyroid weight (approximately 25-40%), which returned to control levels by 3 days. Total thyroid TSH receptor content was assessed by the binding of receptor-purified [125I]bTSH to 15,000 X g fractions of thyroid homogenate. The TSH receptor content paralleled the increase in thyroid weight, with no detectable change in the TSH-binding capacity per mg tissue. Intraperitoneal minipump infusions of bTSH (1 IU/day) over 6 days produced marked and persistent increases in thyroid hormone levels and thyroid weight (greater than 300%) and a similar increase in TSH receptor content. There was no change in the single site equilibrium association constant for bTSH [1.1 X 10(9) M-1 +/- (SE) 9.6 X 10(7) M-1] and no alteration in the binding capacity per mg tissue (67.2 +/- 6.4 pg/mg). Investigation of the in vitro adenylate cyclase response to bTSH (10 mU/ml) and the production of immunoassayable cAMP showed no difference between thyroid tissue obtained from bTSH-treated animals and that obtained from untreated control animals. These observations demonstrated that TSH exerted a positive regulatory effect on its receptor and, under the in vivo conditions used, failed to induce TSH receptor loss or physiologically important desensitization. Such data may explain how TSH receptor antibodies are able to act as TSH agonists and maintain increased thyroid hormone output in human disease.
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PMID:Positive regulation of the guinea pig thyrotropin receptor. 298 15

Although Ismail-Beigi and Edelman demonstrated in 1971 that thyroid hormones control the activity of Na-K-ATPase in the mammalian kidney, the actual site of this regulation inside the organ was not located. We therefore decided to study the relationship between thyroid hormones and Na-K-ATPase activity in individual nephron segments obtained by microdissection of collagenase-treated rabbit kidneys. For this purpose, the changes in the activity and number of catalytic sites of Na-K-ATPase in response to thyroidectomy or triiodothyronine administration were examined. Eight to 12 days after thyroidectomy, Na-K-ATPase activity had dropped by 40 to 80% in the convoluted and straight portions of the proximal tubules, and in the cortical and outer medullary collecting tubules, but not in the thick ascending limbs of Henle's loops or distal convoluted tubules. The apparent number of catalytic sites for Na-K-ATPase, as measured by specific binding of 3H-ouabain, decreased in parallel with Na-K-ATPase activity, and therefore this enzyme's specific activity was not altered. Fourty eight hours after injection of thyroidectomized animals with a single dose of either 100 or 500 micrograms/kg triiodothyronine, Na-K-ATPase activity in target segments was restored to the level measured in control animals. These effects of thyroid hormone were specific for Na-K-ATPase, since the activity of adenylate cyclase, another marker of the basolateral membrane, was not altered by thyroidectomy. The results obtained indicate that triiodothyronine controls Na-K-ATPase activity in specific nephron segments, by altering the number of this enzyme's catalytic sites.
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PMID:Sites of thyroid hormone action on Na-K-ATPase along the rabbit nephron. 299 94

Previously, in this laboratory, we established the presence of alpha and beta adrenergic receptors in primary cultures of neonatal rat heart cells. We now report that exposure to 1-triiodothyronine (10 nM) regulates the binding characteristics of these receptors. As measured by [125I]-I-2-[beta-(4-hydroxyphenyl)ethylaminomethyl]tetralone ([125I]IBE 2254), alpha receptor number (Bmax) decreased by 50% from 37,000 +/- 4,500 to 18,000 +/- 4,300 sites per cell and the equilibrium dissociation constant (KD) decreased from 420 +/- 24 to 150 +/- 37 pM. As measured by [125I]-iodocyanopindolol ([125I]ICYP), beta receptor number increased by 42% from 12,000 +/- 2,600 to 17,000 +/- 4,000 sites per cell with no accompanying change in affinity. An increase in maximal stimulation of adenylate cyclase activity by isoproterenol was also detected under conditions of excess triiodothyronine. No significant changes in agonist or antagonist affinities for either the alpha or the beta adrenergic receptor were detected in thyroid hormone treated cultures. It can be concluded that in cultured myocardial cells thyroid hormone regulates the characteristics of both alpha and beta adrenergic receptors, but in a strikingly different manner.
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PMID:Regulation of alpha and beta adrenergic receptors by triiodothyronine in cultured rat myocardial cells. 302 86


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