Triiodothyronine increases rat apolipoprotein A-I synthesis and alters high-density lipoprotein composition in vivo

The effects of altered serum 3,3',5-triiodothyronine levels on rat lipoprotein metabolism were examined. Daily injections of the hormone (50 micrograms/100 g body mass) over a period of six days led to an increase of 6.4-fold in the hepatic mRNA level for apolipoprotein(apo)A-I, and a 21% increase in serum apoA-I levels. 12h after a single injection of 3,3',5-triiodothyronine the rate of [14C]leucine incorporation into apoA-I increased 2.1 fold. Conversely, in hypothyroid rats there was a decrease in hepatic mRNA levels for apoA-I and a decreased rate of [14C]leucine incorporation into apoA-I. The increase in hepatic apoA-I mRNA levels following 3,3',5-triiodothyronine treatment occurred prior to significant changes in serum triacylglycerol levels. High-density lipoprotein (HDL) particles isolated from the serum of hyperthyroid rats were smaller and enriched in apoA-I compared to apoA-IV and apoE. Similar changes in HDL composition were observed following in vitro incubations of normal rat serum with purified rat apoA-I. The results suggest that during altered thyroid status, changes in serum HDL size and composition occur in association with significant changes in apoA-I gene expression.     

Hydrogen peroxide induces heat shock protein and proto-oncogene mRNA accumulation in Xenopus laevis A6 kidney epithelial cells

In this study, we examined the effect of hydrogen peroxide on the accumulation of various mRNAs encoding heat shock proteins (hsps) and proto-oncogenes in Xenopus A6 kidney epithelial cells. Hydrogen peroxide treatment enhanced the accumulation of hsp90, hsp70, hsp30, c-jun, c-fos, and actin mRNAs with distinct temporal patterns. Although hsp70, c-fos, and c-jun mRNA levels peaked at 1-2 h before declining, hsp30 and hsp90 mRNA levels were maximal at 4-6 h. Other mRNAs, including heat shock cognate hsc70, immunoglobulin binding protein, and ribosomal L8, were unaffected. Treatment of kidney cells with a combination of mild heat shock plus hydrogen peroxide resulted in a synergistic increase in the relative levels of both hsp70 and hsp30 mRNA, but not hsp90, c-fos, c-jun, or actin. This study suggests that analysis of hsp and proto-oncogene mRNA levels may be of value as molecular biomarkers of oxidative stress associated with various disease states and nephrotoxicity in kidney.     

吗啡耐受和电针耐受时大鼠脑内血管紧张素原的基因表达加速

我们以往的工作表明,脑内血管紧张素Ⅱ(AⅡ)作为一种抗阿片物质参与吗啡耐受和电针耐受。本工作探讨在此过程中脑内AⅡ的基因表达是否加速。采用酚抽提法提取大鼠脑组织总RNA,使用人工合成的寡脱氧核糖核酸探针进行打点杂交。放射自显影结果表明,多次皮下注射吗啡或连续数小时电针的大鼠脑血管紧张素原(Ang)mRNA含量明显升高。在IBAS图象分析仪上,测量各杂交点自显影曝光斑的积分光密度值(I.O.D.)表明,连续注射吗啡1d或4d使Ang mRNA分别增高1倍或8倍;电针3或6h使Ang mRNA分别增高5倍或13倍。说明大鼠经3—4h吗啡或电针处理,即可引起在转录水平上脑内Ang基因表达加强。     

Thyroid hormone induces a nerve-independent precocious expression of fast myosin heavy chain mRNA in rat hindlimb skeletal muscle

The appearance of the mRNA for the adult fast IIB myosin heavy chain (MHC) was examined during postnatal development of rats using an S1 nuclease assay. In normal rats, a large increase in the adult MHC mRNA began at 6-7 days after birth, whereas daily injections of newborn rats with 3 micrograms of triiodothyronine (T3) resulted in a precocious increase of the mRNA as early as 3 days after birth. Injection of a range of doses of T3 demonstrated that a large effect was obtained between 30 and 300 ng of T3/day/rat. Fast myosin protein was also precociously induced over the same range of T3 doses. This effect was also seen in denervated muscles, and muscles responded similarly to the different doses of T3 whether they were denervated or not. These results suggest that either thyroid hormone or some circulating factors induced by thyroid hormone are limiting factors in controlling the neonatal-to-adult fast MHC transition and that these factors may act directly on muscle tissue.     

Progesterone mediated increase in monoamine stores and the regulation of enzymes of biosynthesis and metabolism in the adrenal gland during late pregnancy in the rat.

The influence of repeated injections of progesterone to pregnant rats upon monoamine storage and regulation of enzymes phenylethanolamine-N-methyltransferase (PNMT), monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) was studied. All the pregnant females received progesterone (4 mg/100 g body weight) on 19, 20 and 21 days post-coitum but one group was killed at 21 days of pregnancy and the other one at 0 h parturition. Adrenal epinephrine demonstrated highly significant increase in progesterone treated rats. At the same time norepinephrine content declined significantly from the control value. The activity of enzyme PNMT also showed marked increase in the adrenals of progesterone treated females. Activity of enzyme MAO showed a slight decline after progesterone treatment to pregnant rats. Enzyme COMT in progesterone treateed animals showed decline at 0 h parturition but at 21 days post-coitum it was significantly higher from non-injected females. All the increases and decreases in monoamines and the three enzymes were significant when the results were expressed per adrenal gland or per gram of adrenal. The results suggest that exogenous progesterone administration during late pregnancy increases epinephrine stores by declining monoamine metabolism by MAO and COMT and increasing their synthesis by PNMT which is responsible for N-methylation of norepinephrine to epinephrine.     

Effect of thyroxine and thiourea on cholesterol total lipid and glycogen contents of brain of Singi fish (Heteropneustes fossilis bloch)

Three consecutive days injections of thyroxine of different doses (1, 2 and 4 μg/g of body weight) caused significant increase in cholesterol content of cerebrum of Singi fish at 25°C in comparison to the control. The cholesterol content of cerebellum, midbrain and medulla oblongata was enhanced significantly with higher doses of 2 and 4 μg of thyroxine per g of body weight. The lipid and glycogen contents of whole brain were also found to increase with different doses of thyroxine after three consecutive days injections. These cellular constituents decreased with hypothyroid condition induced by thiourea treatment.The results indicate the thyroid hormonal regulation of lipid and carbohydrate metabolism in brain of Singi fish.     

Chronic Electroconvulsive Seizures Down–Regulate Expression of the Immediate-Early Genes c-fos and c-jun in Rat Cerebral Cortex

Acute seizures and other stimuli that increase neuronal activity cause a rapid induction of the immediate-early genes c-fos and c-jun, also referred to as nuclear proto-oncogenes, in the nervous system. In the present study, rats were administered one or more electroconvulsive seizures (ECS) and the responsiveness of c-fos and c-jun to an acute, "test" seizure was examined. Four hours after a single ECS, the induction of c-fos mRNA by a test seizure was blocked, in agreement with earlier findings, but by 18 h the levels of c-fos mRNA could be reinduced by the test seizure, suggesting that 1 day is sufficient to "reset" the responsiveness of this system. However, it was found that chronic, daily ECS treatments resulted in a time-dependent decrease in the expression of c-fos mRNA in response to a test seizure administered 18 h after the last daily ECS; this effect was maximal after 8-10 days of treatment, at which time the induction of c-fos mRNA by the test seizure was blocked dramatically. Chronic ECS also blocked the induction of c-jun in response to an acute, test seizure. The effect of chronic ECS on levels of Fos protein was also investigated. It was found that basal levels of Fos protein were reduced after chronic (10 days) ECS and were not induced by a test seizure. Because levels of Fos protein remain elevated 4 h after a single seizure this finding suggests that the mechanisms by which acute (4 h) and chronic (8-10 days) ECS block the induction of c-fos may differ.     

The effect of mildronate and related substances on levels of thyroid hormones and some intermediates of lipid and carbohydrate metabolism in hyperthyroid and hypothyroid rats

The effects of mildronate [3(2,2,2-trimethylhydrazinium) propionate dihydrate], γ-butyrobetaine (GBB) and their combination (neomildronate) on the level of thyroid hormones and some intermediates of basal metabolism (free fatty acids, triglycerides, glucose) in serum of laboratory rats with various dysfunctions of thyroid glands including idiopathic hyperfunction and also hypofunction induced by administration of 6-propyl-2-thiouracil (PTU) or L-carnitine administration. Intraperitoneal injections of mildronate (150 mg/kg) during 20 days to male Wistar rats with elevated level of thyroid hormones and basal metabolism normalized thyroxin level and parameters of lipid metabolism in serum. Administration of the compounds studied to rats with hypothyroidism induced by administration of PTU or L-carnitine did not influence natural recovery of the hormonal level. Possible biochemical role of these pharmacological treatments is discussed in terms of in regulation of thyroid gland function.     

Effect of thyroid hormone on the abundance of Na,K-adenosine triphosphatase alpha-subunit messenger ribonucleic acid

The effects of thyroid hormone on Na,K-ATPase alpha-subunit mRNA (mRNA alpha) content and Na,K-ATPase activity were measured in renal cortex, heart, and cerebrum of hypothyroid rats 24 and 72 h after injection of diluent or T3. Use of a cDNA probe complementary to rat brain mRNA alpha in Northern blot analysis revealed a single 26-27 S band in RNA isolated from these three tissues regardless of thyroid status. Tissue mRNA alpha content was estimated by dot blot analysis of whole cell extracts and isolated total RNA. Injection of T3 augmented mRNA alpha content by 2.1- to 2.5-fold in kidney cortex and myocardium at 24 h. After three daily injections of T3, the increases in mRNA alpha were evident despite a global increase in RNA content associated with hypertrophy of these target tissues. Furthermore, the increases in abundance of mRNA alpha after 72 h of T3 treatment correlated with enhancement of Na,K-ATPase activity. In contrast, both mRNA alpha and enzyme activity were invariant in the cerebrum. These data suggest that T3-induced augmentation of Na,K-ATPase activity is mediated, at least in part, by increased mRNA alpha content in target tissues.     

Influence of thyroid hormone on the in vitro translational activity of specific mRNAs in the rat heart

The influence of thyroid hormone on the translational activity of specific cardiac mRNA was determined by in vitro translation of RNA isolated from the heart of normal, hypothyroid, and 3,3',5-triiodo-L-thyronine-injected hypothyroid rats. Proteins synthesized in vitro in the presence of [35S]methionine were separated by two-dimensional gel electrophoresis and quantitated by a novel scanning procedure using digital matrix photometry. A total of 421 translational products were detected by fluorography and changes in the predominance of 12 of these were influenced by the thyroid state of the animals. The relative predominance of 8 species was increased in euthyroid animals, whereas 4 translational products were increased in hypothyroid animals. The majority of these thyroid hormone-related alterations occurred in spot pairs of similar molecular weights, but slightly different isoelectric points. In contrast, the relative predominance of mRNAs coding for the major contractile proteins, light chain 1, light chain 2, tropomyosin, actin, and myosin heavy chain was not altered by the thyroid status of the animals. The relative levels of these abundant mRNA species remained unaltered in spite of a thyroid hormone-related increase in total RNA levels. In vivo effects of thyroid hormone on cardiac RNA levels are complex. In addition to a general increase in total RNA and mRNA levels, increases or attenuations in the predominance of a small number of specific mRNA species are observed when euthyroid and hypothyroid animals are compared.     

RGS mRNA expression in rat striatum: modulation by dopamine receptors and effects of repeated amphetamine administration

Single injections of cocaine, amphetamine, or methamphetamine increased RGS2 mRNA levels in rat striatum by two- to fourfold. The D1 dopamine receptor-selective antagonist SCH-23390 had no effect by itself but strongly attenuated RGS2 mRNA induction by amphetamine. In contrast, the D2 receptor-selective antagonist raclopride induced RGS2 mRNA when administered alone and greatly enhanced stimulation by amphetamine. To examine the effects of repeated amphetamine on RGS2 expression, rats were treated with escalating doses of amphetamine (1.0-7.5 mg/kg) for 4 days, followed by 8 days of multiple daily injections (7.5 mg/kg/2 h x four injections). Twenty hours after the last injection the animals were challenged with amphetamine (7.5 mg/kg) or vehicle and killed 1 h later. In drug-naive animals, acute amphetamine induced the expression of RGS2, 3, and 5 and the immediate early genes c-fos and zif/268. RGS4 mRNA levels were not affected. Prior repeated treatment with amphetamine strongly suppressed induction of immediate early genes and RGS5 to a challenge dose of amphetamine. In sharp contrast, prior exposure to amphetamine did not reduce the induction of RGS2 and RGS3 mRNAs to a challenge dose of amphetamine, indicating that control of these genes is resistant to amphetamine-induced tolerance. These data establish a role for dopamine receptors in the regulation of RGS2 expression and suggest that RGS2 and 3 might mediate some aspects of amphetamine-induced tolerance.     

Myofibrillar protein turnover and urinary N-tau-methylhistidine output. Response to dietary supply of protein and energy.

The urinary excretion of total N-tau-methylhistidine by the growing rat was measured to evaluate the effects of dietary protein and energy restriction on muscle protein turnover in vivo. 2. Young male rats (about 100 g initial wt.) were fed on one of three diets. Group I (controls) received an adequate 18% lactalbumin diet for 28 days, on which they sustained maximum growth. Group II (protein-depleted) was fed for 14 days on 0.5 lactalbumin diet, which caused loss of weight; this was followed by repletion for 14 days with the control diet. Group III (protein-energy restricted) received a 1% lactalbumin diet at one-half the food intake of group II for 14 days, and this was also followed by 14 days of repletion with the control diet. 3. The controls showed a progressive rise in the daily urinary output of N-tau-methylhistidine, which was proportionally slightly less rapid than the body-weight increase. 4. The protein-depleted group II showed a marked and progressive decrease in N-tau-methylhistidine excretion, which was proportionally greater than the fall in body weight; during repletion, N-tau-methylhistidine output rose in parallel with body-weight increase, but it did not reach the value attained by the control group. 5. Group III, restricted in both dietary protein and energy, showed an initial small increase in daily N-tau-methylhistidine output, which contrasted with the sharp loss of body weight during this period. After 11 days on this restricted diet, group III then underwent a decrease in N-tau-methylhistidine output, which persisted into the first 4 days of the repletion period, after which output of the methylated amino acid became the same as for group II. 6. Creatinine output, used as an additional metabolic measure of muscle metabolism, showed a fairly constant relationship to body weight in groups I and II during depletion and repletion. However, rats with protein-energy deficiency (group III) underwent a marked increase in output of creatinine per unit of body weight, which also persisited into the repletion period before it fell to more normal values relative to body weight. 7. Analysis of the N-tau-methylhistidine content of actin isolated from a group of protein-depleted rats revealed a small (5%) but significance (P less than 0.02) decrease relative to well-nourished controls. 8. Hence, the rate of muscle protein degradation, as indicated by changes in urinary N-tau-methylhistidine output, appears to respond sensitively and in opposite directions to insufficiency of protein of energy in the diet.     

Effects of thyroid state on the expression of hepatic thyroid hormone transporters in rats

Liver uptake of thyroxine (T4) is mediated by transporters and is rate limiting for hepatic 3,3',5-triiodothyronine (T3) production. We investigated whether hepatic mRNA for T4 transporters is regulated by thyroid state using Xenopus laevis oocytes as an expression system. Because X. laevis oocytes show high endogenous uptake of T4, T4 sulfamate (T4NS) was used as an alternative ligand for the hepatic T4 transporters. Oocytes were injected with 23 ng liver mRNA from euthyroid, hypothyroid, or hyperthyroid rats, and after 3-4 days uptake was determined by incubation of injected and uninjected oocytes for 1 h at 25 degrees C or for 4 h at 18 degrees C with 10 nM [125I]T4NS. Expression of type I deiodinase (D1), which is regulated by thyroid state, was studied in the oocytes as an internal control. Uptake of T4NS showed similar approximately fourfold increases after injection of liver mRNA from euthyroid, hypothyroid, or hyperthyroid rats. A similar lack of effect of thyroid state was observed using reverse T3 as ligand. In contrast, D1 activity induced by liver mRNA from hyperthyroid and hypothyroid rats in the oocytes was 2.4-fold higher and 2.7-fold lower, respectively, compared with euthyroid rats. Studies have shown that uptake of iodothyronines in rat liver is mediated in part by several organic anion transporters, such as the Na+/taurocholate-cotransporting polypeptide (rNTCP) and the Na-independent organic anion-transporting polypeptide (rOATP1). Therefore, the effects of thyroid state on rNTCP, rOATP1, and D1 mRNA levels in rat liver were also determined. Northern analysis showed no differences in rNTCP or rOATP1 mRNA levels between hyperthyroid and hypothyroid rats, whereas D1 mRNA levels varied widely as expected. These results suggest little effect of thyroid state on the levels of mRNA coding for T4 transporters in rat liver, including rNTCP and rOATP1. However, they do not exclude regulation of hepatic T4 transporters by thyroid hormone at the translational and posttranslational level.     

Role of IL-6 in Exercise Training- and Cold-Induced UCP1 Expression in Subcutaneous White Adipose Tissue

Expression of brown adipose tissue (BAT) associated proteins like uncoupling protein 1 (UCP1) in inguinal WAT (iWAT) has been suggested to alter iWAT metabolism. The aim of this study was to investigate the role of interleukin-6 (IL-6) in exercise training and cold exposure-induced iWAT UCP1 expression. The effect of daily intraperitoneal injections of IL-6 (3 ng/g) in C57BL/6 mice for 7 days on iWAT UCP1 expression was examined. In addition, the expression of UCP1 in iWAT was determined in response to 3 days of cold exposure (4°C) and 5 weeks of exercise training in wild type (WT) and whole body IL-6 knockout (KO) mice. Repeated injections of IL-6 in C57BL/6 mice increased UCP1 mRNA but not UCP1 protein content in iWAT. Cold exposure increased iWAT UCP1 mRNA content similarly in IL-6 KO and WT mice, while exercise training increased iWAT UCP1 mRNA in WT mice but not in IL-6 KO mice. Additionally, a cold exposure-induced increase in iWAT UCP1 protein content was blunted in IL-6 KO mice, while UCP1 protein content in iWAT was lower in both untrained and exercise trained IL-6 KO mice than in WT mice. In conclusion, repeated daily increases in plasma IL-6 can increase iWAT UCP1 mRNA content and IL-6 is required for an exercise training-induced increase in iWAT UCP1 mRNA content. In addition IL-6 is required for a full induction of UCP1 protein expression in response to cold exposure and influences the UCP1 protein content iWAT of both untrained and exercise trained animals.