Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.3.1 (citrate synthase)
 4,488 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study was undertaken to examine the effects of thyroid hormonal deficiency on (1) standard (SMR) and maximal (VO2max) rates of O2 consumption, (2) tissue glycolytic and oxidative capacities and (3) submaximal locomotory endurance in a lizard (Dipsosaurus dorsalis). Surgical thyroidectomy induced hypothyroidism in all animals as determined by levels of plasma thyroxine. Hypothyroid lizards had lower levels of SMR (-48%), VO2max (-16%) and citrate synthase activity in liver, heart and skeletal muscle compared to controls. There was a correlated decrease in locomotory endurance in thyroid-deficient animals. Pyruvate kinase activity (an index of glycolytic capacity) in all tissues, and myofibrillar ATPase activity (an index of contractile velocity) in white iliofibularis muscle, showed no significant changes in thyroid-deficient animals. Thyroid hormones appear to be important in ultimately establishing an animal's capacity for locomotory endurance. These findings suggest a new selective context for understanding the evolution of thyroid function.
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PMID:Reduced aerobic capacity and locomotory endurance in thyroid-deficient lizards. 673 62

Thyroid hormone (TH) is an important regulator of mitochondrial content and activity. As mitochondrial content and properties differ depending on muscle-type, we compared mitochondrial regulation and biogenesis by T3 in slow-twitch oxidative (soleus) and fast-twitch mixed muscle (plantaris). Male Wistar rats were treated for 21 to 27 days with T3 (200 microg/kg/day). Oxidative capacity, regulation of mitochondrial respiration by substrates and phosphate acceptors, and transcription factors were studied. In soleus, T3 treatment increased maximal oxygen consumption (Vmax) and the activities of citrate synthase (CS) and cytochrome oxidase (COX) by 100%, 45%, and 71%, respectively (P < 0.001), whereas in plantaris only Vmax increased, by 39% (P < 0.01). ADP-independent respiration rate was increased in soleus muscle by 216% suggesting mitochondrial uncoupling. Mitochondrial substrate utilization in soleus was also influenced by T3, as were mitochondrial enzymes. Lactate dehydrogenase (LDH) activity was elevated in soleus and plantaris by 63% and 11%, respectively (P < 0.01), and soleus creatine kinase was increased by 48% (P < 0.001). T3 increased the mRNA content of the transcriptional co-activator of mitochondrial genes, PGC-1alpha, and the I and IV COX subunits in soleus. The muscle specific response to thyroid hormones could be explained by a lower content of TH receptors in plantaris than soleus. Moreover, TRalpha mRNA level decreased further after T3 treatment. These results demonstrate that TH has a major effect on mitochondrial content, regulation and coupling in slow oxidative muscle, but to a lesser extent in fast muscle, due to the high expression of TH receptors and PGC-1alpha transcription factor.
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PMID:Differential effects of thyroid hormones on energy metabolism of rat slow- and fast-twitch muscles. 1560 82

Thyroid disease has profound effects on cardiovascular function. Hypo- and hyperthyroidism, for example, are associated with reduced and increased maximal endothelium-dependent vasodilation respectively. We therefore hypothesized that the capacity for vascular nitric oxide (NO) formation is decreased in hypothyroidism and increased in hyperthyroidism. To test this hypothesis, rats were made hypothyroid (HYPO) with propylthiouracil or hyperthyroid (HYPER) with triiodothyronine over 3-4 months. Compared with euthyroid control rats (EUT), HYPO exhibited blunted growth and lower citrate synthase activity in the soleus muscle; HYPER exhibited left ventricular hypertrophy and higher citrate synthase activity in the soleus muscle (P<0.05 for all effects). The capacity for NO formation was determined in aortic extracts by formation of [3H]L-citrulline from [3H]L-arginine, i.e. NO synthase (NOS) activity. Thyroid status modulated NOS activity (EUT, 36.8 +/- 5.5 fmol/h per mg protein; HYPO, 26.0 +/- 7.9; HYPER, 64.6 +/- 12.7; P<0.05, HYPER vs HYPO). Expression of endothelial and neural isoforms of NOS was modulated by thyroid status in a parallel fashion. Capacity for responding to NO was also determined via measuring cGMP concentration in aortae incubated with sodium nitroprusside. Stimulated cGMP formation was also modulated by thyroid status (EUT, 73.0 +/- 20.2 pmol/mg protein; HYPO, 152.4 +/- 48.7; HYPER, 10.4 +/- 2.6; P<0.05, HYPER vs HYPO). These data indicate that thyroid status alters capacities for both formation of and responding to NO. The former finding may contribute to previous findings concerning vascular function in thyroid disease states.
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PMID:Thyroid status and nitric oxide in rat arterial vessels. 1581 32

Thyroid hormone (TH) induces marked changes in the biochemical and physiological functioning of cardiac muscle affecting its bioenergetics, contractility and structure. Using a time-course analysis of in vitro treatment of neonatal rat cardiomyocytes with triiodothyronine (T3), mitochondrial biogenesis, functional bioenergetics and cardiomyocyte hypertrophic phenotype were assessed. Activity of respiratory complexes II, IV, V and citrate synthase (CS), levels of mitochondrial enzyme subunits (e.g. COXI, COXIV) and nuclear-encoded transcription factors, involved in mitochondrial biogenesis (e.g. PGC-1, mtTFA and PPAR-alpha), were significantly elevated with 72 h T3 treatment. A time-course analysis showed an early increase (between 3 and 12 h) in activity and levels of subunits of complex IV and V, mitochondrial Ca2+ accumulation and a late increase (at 72 h) in complex II and CS activities, mitochondrial protein content and mitochondrial respiration. Based on overall protein content and specific peptide levels (e.g. actin or myosin) only mild cardiomyocyte hypertrophy was detected. T3 mediates an early stimulation of enzymes containing mtDNA encoded subunits (e.g. complex IV and V) in contrast to a different regulatory pattern for the entirely nuclear-encoded enzymes (e.g. CS and complex II). T3-regulation was similar in both neonatal and young adult cardiomyocytes (ARCM) but absent in the senescent cardiomyocytes. This model offer an opportunity to study the rapid timing of events involved in myocardial cell signaling, bioenergetics and growth dynamics in a timeframe not available with whole animal studies.
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PMID:Nuclear-mitochondrial cross-talk in cardiomyocyte T3 signaling: a time-course analysis. 1589 63