Hyperthyroid Liver Research Articles

Evaluating Hyperthyroidism-Induced Liver Injury Based on In Situ Fluorescence Imaging of Glutathione and Phosphate via Nano-MOFs Sensor

Hyperthyroidism-induced liver injury is quite common in clinical settings. Therefore, developing rapid and simple methods for the assessment of hyperthyroid liver injury is of great significance. Considering phosphorus metabolism is disordered because of hyperthyroidism, and the hyperthyroid liver injury is closely related to the abnormal level of glutathione (GSH). Thus, development of a new method that can simultaneously detect changes in blood phosphorus and GSH levels of serum, liver, kidney, and other organs to assess the degree of hyperthyroid liver injury is necessary for clinical medical research. Herein, a novel fluorescent metal-organic frameworks (MOFs) nanoprobe using the UiO-66(OH)2 as core and Cu-MOFs as shell was designed and synthesized. Through the specific action between Zr (IV) and phosphate, and the combine interaction of MOFs active center Cu (II) and GSH, high sensitivity and specific fluorescence detection of phosphate and GSH were achieved, respectively. Finally, the nanosensor was applied for evaluating different degrees of hyperthyroid liver injury in mice models and realized the monitoring of serum, liver, kidney, and other organs' blood phosphorus and GSH levels, and found that the levels of phosphate and GSH in serum were negatively correlated with the degree of hyperthyroid liver injury, while the changes of phosphate and GSH levels in the liver and kidney organs were positively correlated with the degree of hyperthyroid liver injury. In general, the present works provide a new way to effectively evaluate liver injury induced by hyperthyroidism in the early clinical stage.

Effect of thyroid state on enzymatic and non-enzymatic processes in H2O2 removal by liver mitochondria of male rats

We investigated thyroid state effect on capacity of rat liver mitochondria to remove exogenously produced H2O2, determining their ability to decrease fluorescence generated by an H2O2 detector system. The rate of H2O2 removal by both non respiring and respiring mitochondria was increased by hyperthyroidism and decreased by hypothyroidism. However, the rate was higher in the presence of respiratory substrates, in particular pyruvate/malate, indicating a respiration-dependent process. Generally, the changes in H2O2 removal rates mirrored those in H2O2 release rates excluding the possibility that endogenous and exogenous H2O2 competed for the removing system. Pharmacological inhibition revealed thyroid state-linked differences in antioxidant enzyme contribution to H2O2 removal which were consistent with those in antioxidant system activities. The H2O2 removal was only in part due to enzymatic systems and that imputable to non-enzymatic processes was higher in hyperthyroid and lower in hypothyroid mitochondria. The levels of cytochrome c and the light emissions, due to luminol oxidation catalyzed by cytochrome/H2O2, exhibited similar changes with thyroid state supporting the idea that non-enzymatic scavenging was mainly due to hemoprotein action, which produces hydroxyl radicals. Further support was obtained showing that the whole antioxidant capacity, which provides an evaluation of capacity of the systems, different from cytochromes, assigned to H2O2 scavenging, was lower in hyperthyroid than in hypothyroid state. In conclusion, our results show that mitochondria from hyperthyroid liver have a high capacity for H2O2 removal, which, however, leading in great part to more reactive oxygen species, results harmful for such organelles.

Thiol redox status critically influences mitochondrial response to thyroid hormone‐induced hepatic oxidative injury: A temporal analysis

Liver is a major target organ for thyroid hormone. The objective of the present study was to investigate temporal regulation of mitochondrial glutathione and protein-bound thiol redox status in hyperthyroid liver. Mitochondria were isolated from control and hyperthyroid rat liver tissues at different time intervals, i.e., 24, 72, and 120 h following treatment, and sub-fractionated into sub-mitochondrial particles (SMPs) and matrix fractions. Increased prooxidant levels were indicative of oxidative stress in hyperthyroid mitochondria. Sensitivity to membrane lipid peroxidation (LPx) was maximal after 24 h, which subsided with time. Oxidative damage to proteins was evident as high carbonylation after 72 h; thiol residue damage was an early phenomenon. Reduced and oxidized glutathione (GSH and GSSG) pools of mitochondria were progressively depleted, thereby, impairing matrix antioxidant capacity. However, adaptations to withstand oxidative challenge were elicited in both SMPs and matrix fractions over the long term. It is concluded that maintenance of appropriate intra-mitochondrial glutathione and protein-bound thiol redox status could be instrumental in attenuating thyroid hormone-induced oxidative stress.

Hyperthyroidism induces apoptosis in rat liver through activation of death receptor-mediated pathways

The molecular basis of hepatic dysfunction in thyrotoxicosis is not fully understood. Here, we investigated the effect of altered thyroidal status on death receptor pathways including p75 neurotrophin receptor (p75NTR), a member of tumor necrosis factor (TNF) receptor superfamily, in rat liver. Hyperthyroidism was induced in Sprague-Dawley rats by daily injections of triiodothyronine in a dose of 12.5 microg/100 g body weight for 10 days. Terminal deoxynucleotide-transferase-mediated dUTP nick end labeling assay and caspase-3 activation data confirmed apoptosis in hyperthyroid rat liver. We observed the elevated levels of death ligands, TNF-alpha, Fas ligand and their cognate receptors, TNF-receptor-1 and Fas, and 8-fold increase in caspase-8 activation in hyperthyroid rat liver (p<0.001). We demonstrated for the first time that hyperthyroidism elevates p75NTR levels and its ligands, pro-nerve growth factor and pro-brain-derived neurotrophic factor, in rat liver. Further we showed that most of the apoptotic cells in hyperthyroid liver express p75NTR. We also demonstrated that triiodothyronine administration to rats causes NF-kappaB activation, but persistent exposure (10 days) to triiodothyronine deactivates NF-kappaB leading to sustained c-Jun N-terminal kinase (JNK) activation. This study showed that hyperthyroidism-induced apoptosis in rat liver involves the activation of death receptor-mediated pathways, including p75NTR.

Oxidative Damage to Nuclear DNA in Hyperthyroid Rat Liver: Inability of Vitamin C to Prevent the Damage

The effects of hyperthyroidism on oxidative DNA damage in liver tissue and modification by vitamin C supplementation were investigated in rats. Animals were rendered hyperthyroid by administration of l-thyroxine (0.4 mg/100 g food) for 25 d. In the plasma samples, T3, T4, and thyroid-stimulating hormone (TSH) were measured by radioimmunoassay and ascorbate spectrophotometrically. Oxidative damage to hepatic nuclear DNA was determined by measuring deoxy-guanosine (dG) and 8-oxodG by high-performance liquid chromatography with diode array detector electrochemical detection (HPLC-DAD-ECD). In hyperthyroidism, 8-oxodG/ (105 dG) levels were significantly higher and plasma vitamin C levels lower than in control rats. The results of this experimental study show that oxidative damage to hepatic nuclear DNA increases in the hyperthyroid state and that vitamin C was not effective in preventing this damage.

Thyroid Hormone Regulates the Acetyl-CoA Carboxylase PI Promoter

The acetyl-CoA carboxylase-α gene has two promoters, PI and PII. A variety of mRNA products result from this gene, depending on promoter usage and splicing events. We have investigated thyroid hormone regulation of acetyl-CoA carboxylase-α gene expression, using the reverse-transcription polymerase chain reaction with PI- or PII-specific primers. RNA was extracted from a range of tissues taken from hypo-, eu-, or hyperthyroid rats. PII-generated products were found in all tissues examined at similar levels and were not affected by thyroid state. Products derived from PI were also widely found but with more variable levels of expression. PI mRNAs were reduced in hypo- and elevated in hyperthyroid livers. In brown adipose tissue, more PI products were found in hypothyroid animals. Thus, thyroid hormone regulates the activity of the acetyl-CoA carboxylase PI promoter to influence fatty acid synthesis in a tissue-specific manner.

EFFECT OF HYPERTHYROIDISM ON THE IN VITRO METABOLISM AND COVALENT BINDING OF 1,1-DICHLOROETHYLENE IN RAT LIVER MICROSOMES

Hyperthyroidism potentiates the in vivo hepatotoxicity of 1,1-dichloroethylene (DCE) in rats, with a concomitant increase in [14C]-DCE covalent binding. The enhanced injury produced in hyperthyroid livers by DCE could be due to alterations in either the bioactivation or detoxication phases of DCE metabolism. Previous in vitro studies suggested that hyperthyroidism did not potentiate DCE hepatotoxicity by increasing DCE oxidation to intermediates which were able to covalently bind. Several factors, however, that could contribute to the magnitude of DCE bioactivation or covalent binding were not examined. Our objectives were to characterize the effects of hyperthyroidism in male Sprague-Dawley rats on: (1) covalent binding of [14C]-DCE to microsomes and other subcellular fractions, (2) microsomal mixed-function oxidase (MFO) and glutathione S-transferase (GST) activities, and (3) inactivation of microsomal enzyme activities by presumptive DCE reactive intermediates. Hyperthyroid (HYPERT) and euthyroid (EUT) rats received 3 sc injections of thyroxine (100 µg/100 g) or vehicle, respectively, at 48-h intervals; microsomes and other subcellular fractions were isolated from HYPERT and EUT livers 24 h after the last injection. [l4C]-DCE-derived covalent binding was consistently greater in EUT than HYPERT microsomes. The absence of NADH, and the addition of low concentrations (0.1 and 0.5 mM), but not higher concentrations (>l mM), of glutathione (CSH) diminished covalent binding to a greater extent in HYPERT than EUT microsomes. Covalent binding in mitochondrial, nuclear, and cytosolic fractions of EUT and HYPERT livers was equivalent. Regression analysis of covalent binding to liver cell fractions from both EUT and HYPERT rats showed a significant correlation with P-450 content. Hyperthyroidism decreased microsomal, but not mitochondrial, cytochrome P-450 content, and MFO activities for 7-ethoxycoumarin and benzphetamine were similarly decreased. Hyperthyroidism also diminished microsomal CST activity, and altered CST kinetics for both CSH and 1-chloro-2,4-dinitrobenzene (CDNB). The magnitude of inactivation of MFO and CST activities in the presence of DCE (presumably by DCE reactive intermediates) was comparable between EUT and HYPERT microsomes. When covalent binding was standardized to cytochrome P-450 concentrations in microsomes and mitochondria, HYPERT fractions exhibited slightly greater covalent binding than EUT fractions, suggesting that hyperthyroidism does not reduce the capacity of P-450 hemoproteins to bioactivate DCE. Thus, potentiation of DCE hepatotoxicity by hyperthyroidism may be predominantly due to diminished Phase II constituents, and major increases in reactive intermediate/conjugates that covalently bind to and impair critical cellular molecules.

Adaptive changes in transmembrane transport and metabolism of triiodothyronine in perfused livers of fed and fasted hypothyroid and hyperthyroid rats

The transport and subsequent metabolism of triiodothyronine (T 3) were studied in isolated perfused livers of euthyroid, hypothyroid, and hyperthyroid rats, both fed and 48-hour-fasted. T 3 kinetics (transport and metabolism) during perfusion were evaluated by a two-pool model, whereas the metabolism of T 3 was also investigated by determination of T 3 breakdown products by chromatography of medium and bile. For comparison of groups, metabolism was corrected for differences in transport. Transport parameters in fed hypothyroid livers were not significantly changed as compared with euthyroid livers, whereas metabolism was decreased. In fed hyperthyroid livers, fractional transfer rate constants for influx (k 21) and efflux (k 12) were decreased and metabolism, corrected for differences in intracellular mass transfer, was increased. Furthermore, for transport in hyperthyroid livers it was shown that only total mass transfer (TMT) into the metabolizing liver compartment (not into the nonmetabolizing liver compartment) was decreased. Transport and metabolic parameters in fasted hypothyroid livers were decreased as compared with euthyroid fed livers. In fasted hyperthyroid livers, transport and metabolism were not significantly different as compared with that in euthyroid fed livers, so transport was increased versus hyperthyroid fed livers. It appeared therefore that fasting normalized the effects of hyperthyroidism on both the transport and metabolic processes of T 3 in the liver. The present study demonstrates normal transport and decreased metabolism in livers of hypothyroid fed rats and decreased transport and increased metabolism in livers of hyperthyroid fed rats. In livers of hypothyroid fasted rats transport and metabolism were decreased, whereas in livers of hyperthyroid fasted rats transport and metabolism were not significantly different from that in euthyroid fed livers. These changes might favor tissue euthyroidism despite the altered thyroid and nutritional state, and can therefore be seen as adaptation mechanisms to these altered states at the tissue level.

Nuclear localization and hepatic zonation of rat "spot 14" protein: immunohistochemical investigation employing anti-fusion protein antibodies.

S14 protein and mRNA levels are rapidly regulated by hormones and diet. We have purified a 45-Kd fusion protein from lysates of transformed E. coli that includes the entire S14 polypeptide. Affinity-purified rabbit anti-fusion protein antibodies were used in immunohistochemistry to determine the distribution of S14 protein across the hepatic lobule, and to reassess its intracellular location. In hyperthyroid liver, S14 protein clustered near the central venous zone, and was not detectable in the periportal area of the acinus. The signal in perivenous hepatocytes was primarily nuclear in location, in stark contrast to previous subcellular fractionation studies. Visualization of identical hepatic distribution and subcellular localization employing anti-synthetic peptide antiserum provided evidence for the specificity of the immunostaining, as did attenuation of the signal by preincubation of the antibody with its antigen. No staining was observed in sections of heart or hypothyroid liver, as expected from the low levels of S14 protein in those tissues. The data indicate that induction of S14 protein expression by T3 occurs through enhanced expression by perivenous hepatocytes, rather than by recruitment of cells in more peripheral zones of the lobule. Nuclear localization of the S14 protein by immunohistochemistry suggests that it is lost from nuclei during standard fractionation procedures, and prompts consideration of a role for S14 in regulation of nuclear structure and/or function.

Nuclear localization and hepatic zonation of rat "spot 14" protein: immunohistochemical investigation employing anti-fusion protein antibodies

S14 protein and mRNA levels are rapidly regulated by hormones and diet. We have purified a 45-Kd fusion protein from lysates of transformed E. coli that includes the entire S14 polypeptide. Affinity-purified rabbit anti-fusion protein antibodies were used in immunohistochemistry to determine the distribution of S14 protein across the hepatic lobule, and to reassess its intracellular location. In hyperthyroid liver, S14 protein clustered near the central venous zone, and was not detectable in the periportal area of the acinus. The signal in perivenous hepatocytes was primarily nuclear in location, in stark contrast to previous subcellular fractionation studies. Visualization of identical hepatic distribution and subcellular localization employing anti-synthetic peptide antiserum provided evidence for the specificity of the immunostaining, as did attenuation of the signal by preincubation of the antibody with its antigen. No staining was observed in sections of heart or hypothyroid liver, as expected from the low levels of S14 protein in those tissues. The data indicate that induction of S14 protein expression by T3 occurs through enhanced expression by perivenous hepatocytes, rather than by recruitment of cells in more peripheral zones of the lobule. Nuclear localization of the S14 protein by immunohistochemistry suggests that it is lost from nuclei during standard fractionation procedures, and prompts consideration of a role for S14 in regulation of nuclear structure and/or function.

Mitochondrial metabolism in different thyroid states

The protonmotive force, as well as the mitochondrial and cytosolic concentrations of malate, 2-oxoglutarate, glutamate and aspartate, were determined in livers from hypo-, eu- and hyper-thyroid rats, by density-gradient centrifugation of freeze-clamped livers in non-aqueous solvents [Soboll, Akerboom, Schwenke, Haase & Sies (1980) Biochem. J. 192, 951-954]. The mitochondrial/cytosolic pH difference and the membrane potential were significantly enhanced in hyperthyroid livers compared with the hypothyroid state, resulting in an increased protonmotive force in the presence of thyroid hormones [Soboll & Sies (1989) Methods Enzymol. 174, 118-130]. The mitochondrial concentrations of 2-oxoglutarate, glutamate and aspartate were significantly higher in the euthyroid than in the hypothyroid state, but only slightly higher in the hyperthyroid state. Mitochondrial malate, on the other hand, increased significantly from the hypothyroid to the hyperthyroid state. The mitochondrial/cytosolic concentration gradients were significantly increased in the presence of thyroid hormones only for malate. The changes in steady-state metabolite concentrations reflect a higher substrate supply and a stimulation of mitochondrial metabolism. However, a clear relationship between the increased protonmotive force, as the driving force for mitochondrial metabolite transport, and the subcellular metabolite concentrations is not observable in different thyroid states.

Identification of Rat S14 Protein and Comparison of Its Regulation with That of mRNA S14 Employing Synthetic Peptide Antisera

The rat S14 gene encodes a protein of unknown function and has an amino acid sequence unrelated to any published sequences. Expression of mRNA S14 and lipogenesis in liver, fat, and mammary gland are regulated coordinately by dietary and hormonal stimuli, suggesting that the S14 protein may be associated with lipogenesis. Antisera to synthetic peptides corresponding to portions of the deduced amino acid sequence of the protein were used to identify the protein and to compare its regulation with that of mRNA S14. Antisera specifically recognized the in vitro translation product of mRNA S14 as defined by its migration on two-dimensional gel electrophoresis. A product of identical Mr was identified on Western blots of liver homogenates from hyperthyroid, carbohydrate-fed rats. Subcellular fractionation showed that S14 protein is primarily cytosolic. The protein was detectable in tissues with abundant S14 gene expression, including hyperthyroid liver and epididymal fat and hypothyroid brown adipose tissue, whereas it was undetectable in hypothyroid liver and euthyroid kidney, testis, and spleen. Diurnal variation in hepatic mRNA S14 correlated with comparable changes in levels of the protein. Surprisingly, no S14 protein was observed in the livers of chronically (3 week) hypothyroid rats treated with triiodothyronine (T3) until 12 h had elapsed, despite attainment of maximal levels of mRNA S14 within 4 h. Rapid appearance of protein after T3 treatment was observed in both euthyroid and short term (4 day) hypothyroid rats, suggesting that long-term hypothyroidism is associated with a defect in the translational efficiency of mRNA S14.

Thyroid hormone modulates the introduction of a stop codon in rat liver apolipoprotein B messenger RNA.

Apolipoprotein B (apoB) biosynthesis by rat liver was studied following thyroid hormone (3,5,3'-triiodo-L-thyronine) administration to hypothyroid rats. Pharmacologic doses of 3,5,3'-triiodo-L-thyronine caused suppression of apoB100 synthesis but did not affect apoB48 levels. There was no detectable apoB100 synthesis in hyperthyroid rats. To examine whether these results were mediated by the previously demonstrated mechanism of RNA modification (Powell, L. M., Wallis, S. C., Pease, R. J., Edwards, Y. H., Knott, T. J., and Scott, J. (1987) Cell 50, 831-840), the DNA sequence corresponding to the C-terminal end of rat apoB48 was determined from rat liver cDNA clones. Rat cDNAs contained a stop codon at an identical position to that found in human and rabbit apoB48 intestinal cDNA. To quantitate the relative amounts of apoB100 and apoB48 message, cDNA was synthesized from hepatic and intestinal apoB RNA and a 207-base pair fragment amplified using the polymerase chain reaction. The products were then differentially hybridized with oligonucleotides specific for apoB100 (containing CAA) or apoB48 (TAA). Control and hypothyroid liver contained approximately equal amounts of CAA and TAA, while hyperthyroid liver contained greater than 90% TAA. All gut samples contained 94-98% TAA. Genomic DNA from rat liver contained only CAA. The results demonstrate that apoB mRNA modification can be hormonally modulated in the adult rat by induction of a mechanism involving substitution of a stop codon into hepatic apoB100 mRNA.

The effect of the thyroid status on the activation of glycogen synthase in liver cells.

Isolated hepatocytes from hyperthyroid and euthyroid rats showed the same rate and extent of activation of glycogen synthase after addition of glucose (10 mM or 60 mM). In liver cells from hypothyroid rats this activation occurred at a 7-fold lower rate. However, complete activation of glycogen synthase occurred eventually in broken-cell preparations from either source during incubation in vitro. Glycogen synthase phosphatase was then quantitatively assayed in liver homogenates with exogenous synthase b as substrate. These assays revealed an increased synthase phosphatase activity (approximately 160%) in the hyperthyroid liver and a decreased activity (to approximately 60%) in the livers from hypothyroid rats. These activity changes involved both the cytosolic and the glycogen-bound synthase phosphatase. The increase in the activity of synthase phosphatase after the administration of T3 became maximal after 48 h. We conclude that thyroid hormones control hepatic glycogen synthesis, at least partly by an effect on synthase phosphatase.

Interrelation between thyroid state and the effect of glucagon on gluconeogenesis in perfused rat livers

The effects of different thyroid states on glucagon/dBcAMP-induced gluconeogenesis from alanine or lactate were investigated in the isolated perfused liver from 24-hr starved rats, (1) Gluconeogenesis from alanine varied with the thyroid state, being increased in hyperthyroidism and decreased in hypothyroidism. (2) Both glucagon and dBcAMP increased glucose production from alanine in euthyroid and even less pronounced in hypothyroid livers, the effect was dose dependent; concomitantly alanine and [ 14C] α-amino-isobutyric acid uptake increased. In hyperthyroid liver, both glucagon and dBcAMP stimulated neither hepatic uptake of alanine and [ 14C] α-amino-isobutyric acid nor gluconeogenesis from alanine. (3) Lactate uptake as well as glucose production from lactate varied with the thyroid state, being increased in the hyper- and decreased in the hypothyroid state. (4) Both glucagon and dBcAMP increased lactate uptake as well as gluconeogenesis from lactate: the effect was even more pronounced in hyperthyroid and reduced in hypothyroid liver. We conclude that the glucogenic effect of glucagon/dBcAMP is reduced in the hypo- and —at unlimited substrate supply —stimulated in the hyperthyroid liver.

Differential effects of alanine on ketogenesis and triacylglycerol formation by isolated perfused livers from euthyroid and hyperthyroid rats

We examined the effects of infusion of alanine on hepatic concentration of glycero-3-phosphate (glycero-3-P) and output of triacylglycerol (TG) by isolated perfused livers from triiodothyronine (T 3)-treated rats. It was expected that because of its gluconeogenic and antiketogenic properties, alanine might stimulate accumulation of glycero-3-P, which in turn might result in enhanced TG production by the hyperthyroid livers. The hepatic concentration of glycero-3-P is lower in livers from T 3-treated rats than in euthyroid rats. Infusion of 1.83 and 4.23 mmol alanine/4 h did not alter the hepatic concentration of glycero-3-P and output of triacylglycerol by livers from T 3-treated rats. However in these livers, the two concentrations of infused alanine increased the output of glucose and decreased the output of ketone bodies. In livers from euthyroid animals, the infusion of 1.83 mmol alanine/4 h had no effect, whereas 4.23 mmol/4 h decreased hepatic concentration of glycero-3-P. These concentrations of alanine did not alter the output of ketone bodies or TG, but progressively decreased the output of glucose by the euthyroid livers. Our data suggested that the decreased availability of glycero-3-P in livers from T 3-treated rats is rate-limiting for TG production and correlated with the diminished output of TG, whereas in livers from euthyroid rats, the glycero-3-P concentration is sufficient to maintain maximal synthesis and secretion of TG. Furthermore, the effects of alanine on the output of ketone bodies or glucose appear to be independent of its effects on hepatic glycero-3-P.

Thyroid hormone action on intermediary metabolism

In their physiological concentrations, thyroid hormones stimulate the synthesis as well as the degradation of proteins, whereas in supraphysiological doses protein catabolism predominates. In hyperthyroidism skeletal muscle protein stores suffer depletion which is reflected by an increased urinary N- and methylhistidine -excretion. Due to the enhanced skeletal muscle amino acid release, the plasma concentration of glucoplastic amino acids are often enhanced, contributing by means of an elevated substrate supply to the increased hepatic gluconeogenesis. Thyroid hormone excess induces cardiac hypertrophy which is in direct contrast to the hypotroph skeletal muscle in hyperthyroid patients. Thyroid hormones stimulate a series of intracellular and secretory proteins in the liver, although in hyperthyroid liver alcohol dehydrogenase and the enzymes of histidine and tryptophan metabolism show reduced activities. The stimulatory effect is due to thyroid hormone-induced increase in the protein synthesis at a pretranslational level and is supported experimentally for malic enzyme, alpha 2u-globulin and albumin by the measurement of their specific messenger RNA activities. Thyroid hormone action at the cellular level is reflected by a generalized increase in total cellular RNA with a selective increase or decrease in a small population of specific mRNA. The activities of protein catabolizing lysosomal enzymes are stimulated by thyroid hormones; up to now effects of T3 on the degradation of specific enzymes have not been reported. Serum total protein concentration is slightly reduced or even unchanged in hyperthyroidism. The thyroid hormone-induced increase in the turnover of total body protein is part of the hypermetabolism observed in hyperthyroidism.

Effect of thyroid state on ketogenic capacity of the isolated perfused liver of starved rats

The effect of different thyroid states on the oxidation of free fatty acids was investigated in the isolated perfused liver of 24-h-starved rats. 1. Compared with the euthyroid control the oxidation of oleate to ketone bodies as well as to CO 2 was increased in hyper-, while it was unchanged in hypothyroid livers. 2. The addition of camitine stimulated oleate oxidation in livers from eu- and hyperthyroid rats, but was without effect in hypothyroid livers. 3. Glucose did not affect the thyroid hormone-mediated effect of oleate conversion to ketone bodies. 4. Hepatic oxidation of octanoate was similar in all thyroid states. 5. Re-esterification of oleate was enhanced in hypo-, but reduced in hyperthyroidism. 6. The concentration of hepatic malonyl-CoA was decreased in hypo- and unchanged in hyperthyroid livers. 7. The concentration of cyclic AMP was elevated in the liver of hyperthyroid rats, no differences were observed between eu- and hypothyroid livers. However, increasing the hepatic cyclic AMP content by the addition of glucagon did not stimulate ketogenesis in eu- and hypothyroid livers. 8. The results indicate that thyroid hormones stimulate oleate oxidation by an accelerated transport of its CoA derivative into the mitochondrial compartment.

Effect of hyperthyroidism and hypothyroidism on lipid and carbohydrate metabolism of the perfused rat liver.

1. Liver from hyper- and hypo-thyroid male fed rats were perfused with whole blood and their metabolism was compared with euthyroid controls. 2. Hyperthyroid livers produced more bile than controls and hypothyroid livers produced less. 3. Glucose output by all livers was similar; glycogen declined only during perfusion of hyperthyroid livers. Lactate uptake increased in hyperthyroid but decreased in hypothyroid livers. These results may be explained by changes in oxidation of carbohydrate rather than in gluconeogenesis. 4. Secretion of triacylglycerol was decreased in hyperthyroid and not changed significantly in hypothyroid livers. 5. Fractional extraction of infused [1-14C]oleate was unaltered. Hyperthyroid livers oxidized more oleate to CO2 and ketone bodies, esterified less and incorporated less into lipoproteins of d less than 1.006. Hypothyroid livers oxidized and esterified oleate to the same extent as controls; their decreased O2 consumption was due to diminished oxidation of other (non-lipid) substrates; 14C-labelled ketone-body formation was increased, but at the expense of 14CO2 production. 6. Lipogenesis (measured with 3H2O) was unaltered in hyperthyroid but was decreased in hypothyroid livers. Incorporation of 3H and 14C into triacylglycerol relative to phospholipid decreased in hyperthyroid and increased in hypothyroid livers. Cholesterol synthesis was similar in all perfusions. 7. During oleate infusion, the cytosolic redox state, as indicated by the perfusate [lactate]/[pyruvate] ratio, was decreased in hyperthyroid and increased in hypothyroid livers. No change in [3-hydroxybutyrate]/[acetoacetate] was detected. 8. The importance of relating the concentration of plasma non-esterified fatty acids to the interpretation of metabolic data obtained under differing thyroid status is emphasized.

Thyroid hormone-induced changes in gluconeogenesis and ketogenesis in perfused rat liver.

The regulation of ketogenesis and gluconeogenesis was studied in isolated, perfused livers from hyper- and euthyroid rats. Experimental conditions were varied with respect to lactate and fatty acid concentration in the perfusion medium and with respect to the nutritional state of the rats. 1. The rate of uptake of oleate in perfused livers was independent of the thyroid and nutritional states of the animals. 2. In livers from 48-h-fasted rats no difference was found in rates of ketogenesis between the euthyroid and hyperthyroid livers except when 10 mM lactate was present in the perfusate. In recently fed rats the rates of ketogenesis from oleate (1 mM) and endogenous substrates were low in euthyroid livers (0.45 and 0.05 mumol/min per g liver, respectively), while these rates in hyperthyroid livers were (1.333 and 0.136 mumol/min per g liver, respectively). With octanoate as substrate, high rates of ketogenesis were found in recently fed livers from both euthyroid and hyperthyroid rats (1.573 and 1.717 mumol/min per g liver, respectively). 3. Without oleate in the perfusion medium the rate of gluconeogenesis from low (1 mM) lactate concentrations in livers from 48 h-fasted-rats was slightly increased in the hyperthyroid state (0.548 mumol/min per g liver) compared to the euthyroid state (0.408 mumol/min per g liver). When lactate concentration in the perfusion medium was raised to 10 mM the rate of gluconeogenesis was increased 4-fold in the hyperthyroid livers (1.800 mumol/min per g liver) but only 20% in the euthyroid livers (0.490 mumol/min per g liver). The presence of oleate (1 mM) had no effect on the rate of gluconeogenesis from low lactate concentrations in livers form 48-h-fasted animals of either thyroid state. At 10 mM lactate the inclusion of oleate caused a pronounced stimulation of gluconeogenesis in euthyroid livers (from 0.490 to 1.766 mumol/min per g liver) but not in hyperthyroid livers (from 1.800 to 1.973 mumol/min per g liver) so that the difference in the rate of gluconeogenesis between the two thyroid states disappeared. 4. The content of endogenous substrates was measured in liver biopsies taken before perfusion. The glycogen concentration was independent of the thyroid state in 48-h fasted animals. The triglyceride content was independent of the thyroid state in recently fed animals. In recently fed animals the glycogen content was reduced by 90% in hyperthyroid animals, and in 48-h-fasted animals the triglyceride content was reduced by 50% in hyperthyroid animals. 5. The energy cost of gluconeogenesis from lactate appeared to be independent of the thyroid state.