Increased Cytosolic Androgen Receptor Binding in Rat Striated Muscle Following Denervation and Disuse

Abstract: We investigated the effects of denervation and disuse on cytosolic androgen receptor binding by rat striated muscle. Denervation of the extensor digitorum longus and tibialis anterior muscles caused a 40–50% increase in cytosolic androgen receptor concentration with no change in apparent binding affinity. This effect was evident at 6 h postdenervation, maximal at 24 h, and declined to 120% of the control level 72 h after denervation. A 40% increase in cytosolic androgen receptor concentration was also noted 24 hr after denervation of the hormone-sensitive levator ani muscle. The effect of denervation on androgen receptors was not blocked by in vivo injection of cycloheximide; therefore, de novo receptor synthesis probably is not involved in the observed increase. Disuse, produced by subperineurial injection of tetrodotoxin into the tibial and common peroneal branches of the sciatic nerve, mimicked the effect of denervation on androgen receptor binding, suggesting that neuromuscular activity is important in regulation of receptor concentration. Possible mechanisms subserving this effect are discussed.     

大鼠与家兔生后各年龄阶段跖肌纤维的比较

应用建立在肌球蛋白重链异构体基础上的标准肌动球蛋白ATP酶和琥珀酸脱氢酶组织化学方法,分析大鼠和家兔出生后发育各年龄阶段跖肌纤维型分布。在生后2周至24周龄的大鼠和家兔Ⅰ、ⅡX型肌纤维百分比例减少,而ⅡA、ⅡB型纤维则增加。进行大量单肌纤维的组织化学特征的比较和相关性探讨。结果显示动物平均体重与跖肌的平均湿重随生后发育逐渐增加,Ⅰ、ⅡX、ⅡA及ⅡB型纤维均在生后各年龄组的全部肌肉内被发现,但出生后2日龄组是个例外。在生后发育期间,雄性大鼠和家兔ⅡB型纤维的平均肌纤维型构成要大于雌性大鼠和家兔,而雄性大鼠和家兔Ⅰ、ⅡX、ⅡA型三种氧化组织化学分类的肌纤维型构成均小于雌性大鼠和家兔。大鼠Ⅰ、ⅡX、ⅡA和ⅡB型纤维的平均横切面积显然要比家兔的同类型肌纤维要小。在大鼠和家兔可见明显的性别差异。大鼠和家兔的ⅡX型纤维横切面积是最小的,Ⅰ、ⅡA型纤维呈中等大小,ⅡB型纤维最大。该重要的测试有助于我们深入研究啮齿类动物快肌纤维生理特征的适应。     

A Dietary Supplementation with Leucine and Antioxidants Is Capable to Accelerate Muscle Mass Recovery after Immobilization in Adult Rats

Prolonged inactivity induces muscle loss due to an activation of proteolysis and decreased protein synthesis; the latter is also involved in the recovery of muscle mass. The aim of the present work was to explore the evolution of muscle mass and protein metabolism during immobilization and recovery and assess the effect of a nutritional strategy for counteracting muscle loss and facilitating recovery. Adult rats (6–8 months) were subjected to unilateral hindlimb casting for 8 days (I0–I8) and then permitted to recover for 10 to 40 days (R10–R40). They were fed a Control or Experimental diet supplemented with antioxidants/polyphenols (AOX) (I0 to I8), AOX and leucine (AOX + LEU) (I8 to R15) and LEU alone (R15 to R40). Muscle mass, absolute protein synthesis rate and proteasome activities were measured in gastrocnemius muscle in casted and non-casted legs in post prandial (PP) and post absorptive (PA) states at each time point. Immobilized gastrocnemius protein content was similarly reduced (-37%) in both diets compared to the non-casted leg. Muscle mass recovery was accelerated by the AOX and LEU supplementation (+6% AOX+LEU vs. Control, P<0.05 at R40) due to a higher protein synthesis both in PA and PP states (+23% and 31% respectively, Experimental vs. Control diets, P<0.05, R40) without difference in trypsin- and chymotrypsin-like activities between diets. Thus, this nutritional supplementation accelerated the recovery of muscle mass via a stimulation of protein synthesis throughout the entire day (in the PP and PA states) and could be a promising strategy to be tested during recovery from bed rest in humans.     

Effects of Nandrolone in the Counteraction of Skeletal Muscle Atrophy in a Mouse Model of Muscle Disuse: Molecular Biology and Functional Evaluation

Muscle disuse produces severe atrophy and a slow-to-fast phenotype transition in the postural Soleus (Sol) muscle of rodents. Antioxidants, amino-acids and growth factors were ineffective to ameliorate muscle atrophy. Here we evaluate the effects of nandrolone (ND), an anabolic steroid, on mouse skeletal muscle atrophy induced by hindlimb unloading (HU). Mice were pre-treated for 2-weeks before HU and during the 2-weeks of HU. Muscle weight and total protein content were reduced in HU mice and a restoration of these parameters was found in ND-treated HU mice. The analysis of gene expression by real-time PCR demonstrates an increase of MuRF-1 during HU but minor involvement of other catabolic pathways. However, ND did not affect MuRF-1 expression. The evaluation of anabolic pathways showed no change in mTOR and eIF2-kinase mRNA expression, but the protein expression of the eukaryotic initiation factor eIF2 was reduced during HU and restored by ND. Moreover we found an involvement of regenerative pathways, since the increase of MyoD observed after HU suggests the promotion of myogenic stem cell differentiation in response to atrophy. At the same time, Notch-1 expression was down-regulated. Interestingly, the ND treatment prevented changes in MyoD and Notch-1 expression. On the contrary, there was no evidence for an effect of ND on the change of muscle phenotype induced by HU, since no effect of treatment was observed on the resting gCl, restCa and contractile properties in Sol muscle. Accordingly, PGC1α and myosin heavy chain expression, indexes of the phenotype transition, were not restored in ND-treated HU mice. We hypothesize that ND is unable to directly affect the phenotype transition when the specialized motor unit firing pattern of stimulation is lacking. Nevertheless, through stimulation of protein synthesis, ND preserves protein content and muscle weight, which may result advantageous to the affected skeletal muscle for functional recovery.     

Acetylcholine Synthesis and Release in the Extensor Digitorum Longus Muscle of Mature and Aged Rats

Uptake of labeled choline and its incorporation into acetylcholine (ACh) were assayed at the neuromuscular junction of the extensor digitorum longus (EDL) muscle of rats aged 11 (mature adult) and 27 (aged) months. Under resting conditions, there were no significant differences in muscle ACh or choline levels. Following a 1-h incubation in labeled choline, however, tissue from the younger rats contained significantly greater amounts of labeled choline and labeled ACh; the specific activities of ACh and choline were nearly 10-fold higher in the 11-month-old animals, indicating reduced uptake of labeled choline in the older animals. ACh and choline efflux rates under resting conditions did not change with age, indicating an uncoupling of exogenous choline uptake and ACh efflux in EDL during aging. During nerve stimulation (1 Hz), the amount of labeled choline incorporated into ACh was 150% greater in the aged animals. The specific activity of ACh released during stimulation was correspondingly greater in the 27-month-old animals, although total ACh released did not change appreciably with age. There were no age-related differences in choline acetyltransferase activity. Contrasting results were obtained from diaphragm in previous studies; the linkage between choline uptake and ACh efflux was maintained during rest and stimulation in the diaphragm. Hypothetically, these differences between EDL and diaphragm may be related to their diverse activation patterns: EDL is recruited much less frequently and less regularly than diaphragm, a continually active vital muscle.     

Effects of Oxytocin Administration on Oxidative Markers in the Temporal Lobe of Aged Rats

Neurophysiology - Considering the relevance of oxidative stress in aging and antioxidant properties of oxytocin, which we previously demonstrated, we studied the effects of intraperitoneal oxytocin...     

Effects of Dietary Oxidized Cholesterol on Lipid Metabolism in Differently Aged Rats

Male Sprague-Dawley rats, 4 weeks (young) or 8 months (adult) of age, were fed one of three purified diets free of or containing either 0.5% cholesterol or 0.5% oxidized cholesterol (92% oxidized cholesterol) for 3 weeks. Feeding of oxidized cholesterol caused a significant reduction of food intake, body weight gain, and relative liver weight in rats of both ages. The activity of the HMG-CoA reductase and cholesterol 7α-hydroxylase of liver microsomes, the key enzymes in cholesterol synthesis and catabolism, respectively, was lowered by oxidized cholesterol compared to the diet free of cholesterol in both ages, and the difference was significantly in the adult. On the other hand, the activity of Δ6-desaturase of liver microsomes, a key enzyme in linoleic acid metabolism to arachidonic acid, was significantly increased by oxidized cholesterol in adult rats, leading to the increase in linoleic acid desaturation index [(20:3n-6 + 20:4n-6)/18:2n-6] in liver phospholipids. Oxidized cholesterol reduced the concentration of cholesterol in serum and liver. Also, the fecal excretion of acidic steroids was lower in rats fed the oxidized cholesterol diet than in those fed the cholesterol-free diet. Thus, oxidized cholesterol significantly influenced cholesterol and fatty acid metabolism in particular in adult rats.     

Differential Protein Expression in Aortic Smooth Muscle Cells Cultured from Newborn and Aged Rats

Atherosclerosis is a complex disease in which smooth muscle cells (SMC) play a fundamental role. Work from several laboratories has suggested that in experimental models of atheromatosis SMC heterogeneity is important in the establishment of intimal thickening. Moreover, it has been shown that SMC cultured from different situations in vivo maintain distinct phenotypic features in vitro. In order to find proteins differentially expressed in SMC cultured from newborn and aged rats, total protein extracts were separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), high-resolution maps were built, and differentially expressed spots were identified by automatic computer analysis. Of the 14 differentially expressed protein spots, 4 were present in SMC of newborn and 10 in SMC of old animals; we describe their molecular weights and isoelectric points. One of these proteins (expressed only in cultured SMC of old rats) was successfully microsequenced for 16 amino acids and it was found identical to cellular retinol-binding protein. This result provides, to our knowledge, the first suggestion that retinoids are implicated in the differentiation and aging of vascular SMC.     

Effects of Denervation and Simple Disuse on Rates of Oxidation and on Activities of Four Mitochondrial Enzymes in Type I Muscle

To differentiate the effect of muscle contractile activity from that of motor nerve on oxidative processes in type I muscle, oxidative processes were studied in muscle after immobilization and after denervation. The two processes led to similar atrophy of muscle weight and of the mean diameter of muscle fibers. Disuse of soleus muscle (type I) did not affect rates of oxidation of 14C-labeled substrates although these were reduced by disuse of the vastus lateralis (type II). Disuse of the soleus did not affect activities of several mitochondrial enzymes assayed by histochemical or biochemical methods. However, denervation of the soleus did lead to a fall in metabolic rates and enzyme activities. The activity of 3-hydroxybutyrate dehydrogenase fell more than did the activities of succinic dehydrogenase, lipoamide dehydrogenase, or cytochrome-c oxidase in both homogenates and in mitochondrial fractions. These results suggest nerve may regulate mitochondrial enzymes in type I muscle. The mechanism appears to be different from that which regulates oxidative processes in type II muscle.     

Ulinastatin Alleviates Neuroinflammation but Fails to Improve Cognitive Function in Aged Rats Following Partial Hepatectomy

Postoperative cognitive dysfunction (POCD) is very common complication of surgery in aged individuals. Accumulated evidence suggests that neuroinflammation may be the underlying cause of POCD. The aim of the present study was to investigate the effects of ulinastatin (UTI) on neuroinflammation and on learning and memory of aged rats after anesthesia and surgery. Our results showed that anesthetic isoflurane increased the hippocampal mRNA level of IL-1β, while surgery of partial hepatectomy increased the hippocampal mRNA levels of IL-1β, TNF-α, and IL-6 as well as impaired rats’ spatial memory at day 7 post-surgery. UTI (10,000 U/kg, i.v.) decreased the anesthesia- and surgery-induced increases in mRNA levels of all three cytokines, but did not improve the rats’ impaired working memory. In conclusion, moderate and temporary suppression of UTI-induced inflammatory cytokines in hippocampus is not sufficient to alleviate the impairment of working memory.     

Pretreatment Effect of Resveratrol on Streptozotocin-Induced Diabetes in Rats

This study was planned to investigate the pretreatment effect of resveratrol on streptozotocin-induced diabetic rats. The control group consisted of 10 male albino Sprague–Dawley rats, 10–12 weeks of age, weighing approximately 295 g. The first experimental group consisted of 15 albino Sprague–Dawley rats, 10–12 weeks of age, weighing approximately 305 g. This group was administered streptozotocin (55 mg/kg, intraperitoneally). The second experimental group (n = 15) was administered resveratrol (0.5 ml/day) 10 days before streptozotocin induction. A training period was performed for all groups before the experimental procedure, and systolic arterial blood pressures and heart rates were recorded daily. At the end of the 10th day, blood samples of control and experimental groups were drawn. Total nitrite, nitrite, nitrate, malondialdehyde (MDA), copper, and zinc concentrations in plasma were measured both in control and experimental groups. Additionally, superoxide dismutase, catalase activities, and copper and zinc concentrations in red cell were determined in each group. At the end of the study, increases in catalase activity, nitric oxide level, and zinc concentrations and decreases in lipid peroxidation product MDA and copper concentrations were found in the resveratrol-pretreated diabetic group when compared to the diabetic group. This study was presented at “The 5th International Congress of Pathophysiology (ISP2006)” June 28–July 1, 2006, Beijing, China.     

Adolescent Toluene Inhalation in Rats Affects White Matter Maturation with the Potential for Recovery Following Abstinence

Inhalant misuse is common during adolescence, with ongoing chronic misuse associated with neurobiological and cognitive abnormalities. While human imaging studies consistently report white matter abnormalities among long-term inhalant users, longitudinal studies have been lacking with limited data available regarding the progressive nature of such abnormalities, including the potential for recovery following periods of sustained abstinence. We exposed adolescent male Wistar rats (postnatal day 27) to chronic intermittent inhaled toluene (3,000 ppm) for 1 hour/day, 3 times/week for 8 weeks to model abuse patterns observed in adolescent and young adult human users. This dosing regimen resulted in a significant retardation in weight gain during the exposure period (p<0.05). In parallel, we performed longitudinal magnetic resonance imaging (T₂-weighted) and diffusion tensor imaging prior to exposure, and after 4 and 8 weeks, to examine the integrity of white matter tracts, including the anterior commissure and corpus callosum. We also conducted imaging after 8 weeks of abstinence to assess for potential recovery. Chronic intermittent toluene exposure during adolescence and early adulthood resulted in white matter abnormalities, including a decrease in axial (p<0.05) and radial (p<0.05) diffusivity. These abnormalities appeared region-specific, occurring in the anterior commissure but not the corpus callosum and were not present until after at least 4 weeks of exposure. Toluene-induced effects on both body weight and white matter parameters recovered following abstinence. Behaviourally, we observed a progressive decrease in rearing activity following toluene exposure but no difference in motor function, suggesting cognitive function may be more sensitive to the effects of toluene. Furthermore, deficits in rearing were present by 4 weeks suggesting that toluene may affect behaviour prior to detectable white matter abnormalities. Consequently, exposure to inhalants that contain toluene during adolescence and early adulthood appear to differentially affect white matter maturation and behavioural outcomes, although recovery can occur following abstinence.     

Dexamethasone and BCAA Failed to Modulate Muscle Mass and mTOR Signaling in GH-Deficient Rats

Branched-chain amino acids (BCAAs) and IGF-I, the secretion of which is stimulated by growth hormone (GH), prevent muscle atrophy. mTOR plays a pivotal role in the protective actions of BCAA and IGF-1. The pathway by which BCAA activates mTOR is different from that of IGF-1, which suggests that BCAA and GH work independently. We tried to examine whether BCAA exerts a protective effect against dexamethasone (Dex)-induced muscle atrophy independently of GH using GH-deficient spontaneous dwarf rats (SDRs). Unexpectedly, Dex did not induce muscle atrophy assessed by the measurement of cross-sectional area (CSA) of the muscle fibers and did not increase atrogin-1, MuRF1 and REDD1 expressions, which are activated during protein degradation. Glucocorticoid (GR) mRNA levels were higher in SDRs compared to GH-treated SDRs, indicating that the low expression of GR is not the reason of the defect of Dex’s action in SDRs. BCAA did not stimulate the phosphorylation of p70S6K or 4E-BP1, which stimulate protein synthesis. BCAA did not decrease the mRNA level of atrogin-1 or MuRF1. These findings suggested that Dex failed to modulate muscle mass and that BCAA was unable to activate mTOR in SDRs because these phosphorylations of p70S6K and 4E-BP1 and the reductions of these mRNAs are regulated by mTOR. In contrast, after GH supplementation, these responses to Dex were normalized and muscle fiber CSA was decreased by Dex. BCAA prevented the Dex-induced decrease in CSA. BCAA increased the phosphorylation of p70S6K and decreased the Dex-induced elevations of atrogin-1 and Bnip3 mRNAs. However, the amount of mTORC1 components including mTOR was not decreased in the SDRs compared to the normal rats. These findings suggest that GH increases mTORC1 activity but not its content to recover the action of BCAA in SDRs and that GH is required for actions of Dex and BCAA in muscles.     

Prevention of Disuse Muscle Atrophy by Dietary Ingestion of 8-Prenylnaringenin in Denervated Mice

Flavonoids have attracted considerable attention in relation to their effects upon health. 8-Prenylnaringenin (8-PN) is found in the common hop (Humulus lupulus) and assumed to be responsible for the health impact of beer consumption. We wanted to clarify the effects of prenylation on the physiological functions of dietary flavonoids by comparing the effects of 8-PN with that of intact naringenin in the prevention of disuse muscle atrophy using a model of denervation in mice. Consumption of 8-PN (but not naringenin) prevented loss of weight in the gastrocnemius muscle further supported by the lack of induction of the protein content of a key ubiquitin ligase involved in muscle atrophy, atrogin-1, and by the activation of Akt phosphorylation. 8-PN content in the gastrocnemius muscle was tenfold higher than that of naringenin. These results suggested that, compared with naringenin, 8-PN was effectively concentrated into skeletal muscle to exert its preventive effects upon disuse muscle atrophy. It is likely that prenylation generates novel functions for 8-PN by enhancing its accumulation into muscle tissue through dietary intake.     

The Time Course of the Loss and Recovery of Contracture Ability in Frog Striated Muscle Following Exposure to Ca-Free Solutions

Using area under the contracture curve to quantitate contractures, the diffusion coefficient of calcium ions within the frog toe muscle during washout in a calcium-free solution and subsequent recovery after reintroduction of calcium to the bathing solution was calculated to be about 2 x 10^-6 cm²/sec. The diffusion coefficient measured during washout was found to be independent of temperature or initial calcium ion concentration. During recovery it was found to decrease if the temperature was lowered. This was likely due to the repolarization occurring after the depolarizing effect of the calcium-free solution. The relation between contracture area and [Ca]_o was found to be useful over a wider range than that between maximum tension and [Ca]_o. The normalized contracture areas were larger at lower calcium concentrations if the contractures were produced with cold potassium solutions or if NO₃ replaced Cl in the bathing solutions. Decreasing the potassium concentration of the contracture solution to 50 mM from 115 mM did not change the relation between [Ca]_o and the normalized area. If the K concentration of the bathing solution was increased, the areas were decreased at lower concentrations of Ca.     

白藜芦醇对急性痛风性关节炎大鼠的影响(英文)

目的:观察白藜芦醇对急性痛风性关节炎大鼠的影响。方法:选取Wista大鼠36只,随机分为正常对照组、模型组、秋水仙碱组、白藜芦醇低剂量组、白藜芦醇中剂量组、白藜芦醇高剂量组,各组相应采用生理盐水、秋水仙碱、白藜芦醇低、中、高剂量灌胃7天(1次/日),模型组及各实验组于灌胃第四天把25g/mL(0.05mL)浓度的尿酸盐溶液注射到大鼠踝关节腔内,制备急性痛风性关节炎模型,正常对照组大鼠关节腔内注射生理盐水0.05 ml,72 h后留取踝关节关节液及关节滑膜,应用ELISA法观察关节液中IL-1β、CXCL10的变化。关节滑膜用10%福尔马林固定待做病理。结果:与模型组比较,白藜芦醇能显著降低关节液中IL-1β、CXCL10水平(P0.05),病理结果显示,白藜芦醇可减轻急性痛风性关节炎大鼠踝关节组织的水肿和炎性细胞浸润。结论:急性痛风性关节炎发病过程中IL-1β,CXCL10明显增高,白藜芦醇可有效抑制急性痛风性关节炎发作,且该作用呈一定的剂量依赖性。关键词:痛风性关节炎;白藜芦醇;白介素1-β