Stimulation and inhibition of resting muscle thermogenesis by vasoconstrictors in perfused rat hind limb

Angiotensin (AII) and serotonin (5-HT) are both vasoconstrictors of the constant-flow perfused rat hind limb that have opposite effects on thermogenesis, possibly the result of differing effects on vascular flow distribution between nutritive and non-nutritive pathways. In the present study interaction between the two opposing agents was examined with the expectation that the combined presence would show additive effects on pressure and mutually neutralizing effects on thermogenesis. Thus doses of AII and 5-HT that gave similar, but opposite, quantitative effects on thermogenesis were infused alone, in combination one after the other, or in combination with the order reversed, and the effects on perfusion pressure (PP) and thermogenesis (oxygen uptake, VO2) were compared. AII (3 nM) alone increased PP by 15+/-1 mmHg (1 mmHg = 133.3 Pa) and VO2 by 3.1-/+0.2 micromol.h(-1).g(-1), whereas 5-HT (1 microM) alone increased PP by 75+/-6 mmHg and inhibited VO2 by 3.9+/-0.2 micromol.h(-1).g(-1). When added in combination, the outcome depended on the order of addition. Following AII, infusion of 5-HT further increased PP by 160+/-11 mmHg and decreased VO2 by 6.3+/-0.2 micromol.h(-1)g(-1). Following 5-HT, infusion of AII further increased PP by 28+/-4 mmHg and increased VO2 by only 1.8+/-0.3 micromol.h(-1).g(-1). The prior presence of 5-HT (1 microM) shifted the AII dose-response curves for VO2 and pressure to the right and left, respectively. The prior infusion of AII increased the dose-dependent response to 5-HT in terms of both the inhibition of VO2 and the increase in PP. At low doses of 5-HT (10(-8)-10(-7) M), but not alpha-methyl serotonin (alphaMT), there was a marked vasodilatation-associated inhibition of AII-mediated increase in VO2. Overall the data show that the combined effect of AII and 5-HT differed from the simple addition of each separately. Since the order of addition appears to be critical in terms of thermogenic outcome, it is concluded that each vasoconstrictor exerts a specific hemodynamic action to affect access of the other to vascular receptor sites. These findings are consistent with the previously reported effects of these vasoconstrictors on substrate and insulin access to muscle of the perfused rat hind limb.     

Effect of hind limb muscle unloading on liver metabolism of rats

In response to decreased use, skeletal muscle undergoes an adaptive reductive remodeling. There is a shift in fiber types from slow twitch to fast twitch fiber types. Associated with muscle unloading is an increased reliance on carbohydrate metabolism for energy. The hind limb suspended (HLS) rat model was used as the experimental model to determine whether skeletal muscle unloading had any impact on the liver. We used a combination of actual enzyme assays and microarray mRNA expression to address this question. The GenMAPP program was used to identify altered metabolic pathways. We found that the major changes in the liver with HLS were increases in the expression of genes involved in the generation of energy fuels for export, specifically gluconeogenesis and lipogenesis. The expression of mRNA was increased (P<0.05) for three of the four enzymes involved in the regulation of gluconeogenesis pathway (pyruvate carboxylase (PC), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G-6-Pase). Actual assay of enzymatic activity, in micromol . min(-1) . mg protein(-1) showed G-6-Pase (0.14+0.01 vs 0.17+0.01 P<0.05), fructose 1,6, bisphophosphatase (0.048+0.002 vs 0.054+0.002, P<0.07), and PEPCK (0.031+0.002 vs 0.038+0.012 (P<0.05) to be increased. We conclude that 1) atrophied muscle is not the only tissue to be affected by HLS, as there is also a response by the liver; and 2) the major changes in liver substrate metabolism induced by HLS appear to be limited to glucose and triglyceride production. The increase in glycolytic capacity in disused muscle is paralleled by an increase in glucogenic capacity by the liver.     

振动训练对制动大鼠单一肌梭电生理活动的影响

采用石膏固定建立后肢制动模型,用空气隔绝法记录大鼠单一肌梭的电生理活动,用振动仪给制动+振动组比目鱼肌施加高频振动,7 d后观察大鼠制动侧比目鱼肌肌梭的电生理活动变化。比目鱼肌的湿重与非制动侧相比降低了15.33%±4.76%(P<0.05);有自发放电的肌梭数量减少(P<0.05);静息放电频率降低(P<0.05)。制动期间施加高频振动组,比目鱼肌湿重减少的程度明显降低(P<0.05);自发放电的肌梭数量、肌梭的放电频率明显高于制动组(P<0.05)。制动期间的肌肉振动对制动所致肌梭电生理活动特性的改变有明显的对抗作用。     

The incidence and properties of beta axons to muscle spindles in the cat hind limb.

The distribution of beta axons to muscle spindles in the tenuissimus and abductor digiti quinti medius (A.D.Q.M.) muscles of the hind limb of the cat was determined by testing the action of single motor axons, capable of producing extrafusal contraction, isolated in the ventral spinal roots on the discharges of individual muscle spindle primary sensory endings recorded in the dorsal spinal roots. The proportion of spindles with beta innervation was 41% in A.D.Q.M. and 30% in tenuissimus. The proportion of fast motor axons that were beta axons was 28% in the A.D.Q.M. and 11% in tenuissimus; usually each beta axon innervated a single spindle while no spindle received more than two beta axons. The beta axons were dynamic in nature and those to any one muscle tended to have slightly lower conduction velocities than the alpha axons though some overlap did occur. The extent to which beta axons can account for the fact that in isolated spindles axons selective to either nuclear bag or nuclear chain fibres are found in about equal proportions whereas a ratio of three static to one dynamic gamma axons is found electrophysiologically is discussed. An explanation for the low incidence of beta innervation previously found electrophysiologically and the considerably higher incidence found histologically is given.     

The effect of a nitroxide antioxidant on ischemia-reperfusion injury in the rat in vivo hind limb model

Microsurgical procedures such as free tissue transfer or replantations of amputated digits involve an obligatory ischemic period leading to regional tissue oedema, rhabdomyolysis, systemic acidosis, hypercalcemia and multiple organ dysfunction syndrome reflecting ischemia-reperfusion (I/R) injury. Since nitroxide stable radicals act as antioxidants their potential protective effects were tested. Anaesthetized Sabra rats were subjected to regional ischemia of the hind limb for 2 h using a tourniquet. Upon reperfusion rats were injected with 4-OH-2,2,6,6-tetramethylpiperidine-1-oxyl (TPL). Systemic I/R-induced damage was assessed by sampling blood for differential count, lactate dehydrogenase (LDH) and creatine phosphokinase (CPK) serum levels. Regional injury was evaluated by analysing excised muscle samples for oedema (tissue water content) and inflammatory infiltrate (number of cell nuclei in histomorphometric analysis). I/R-induced changes of biomarkers reflecting systemic damage peaked about 8 h following the start of reperfusion and fully disappeared as the biomarkers relaxed to their pre-ischemic values after 24 h. TPL facilitated the recovery of some of these parameters and partially affected release of cellular CPK and LDH. The parameters of I/R-induced regional tissue injury did not demonstrate any recovery and were not inhibited by TPL.     

The effect of a nitroxide antioxidant on ischemia-reperfusion injury in the rat in vivo hind limb model

Microsurgical procedures such as free tissue transfer or replantations of amputated digits involve an obligatory ischemic period leading to regional tissue oedema, rhabdomyolysis, systemic acidosis, hypercalcemia and multiple organ dysfunction syndrome reflecting ischemia-reperfusion (I/R) injury. Since nitroxide stable radicals act as antioxidants their potential protective effects were tested. Anaesthetized Sabra rats were subjected to regional ischemia of the hind limb for 2 h using a tourniquet. Upon reperfusion rats were injected with 4-OH-2,2,6,6-tetramethylpiperidine-1-oxyl (TPL). Systemic I/R-induced damage was assessed by sampling blood for differential count, lactate dehydrogenase (LDH) and creatine phosphokinase (CPK) serum levels. Regional injury was evaluated by analysing excised muscle samples for oedema (tissue water content) and inflammatory infiltrate (number of cell nuclei in histomorphometric analysis). I/R-induced changes of biomarkers reflecting systemic damage peaked about 8 h following the start of reperfusion and fully disappeared as the biomarkers relaxed to their pre-ischemic values after 24 h. TPL facilitated the recovery of some of these parameters and partially affected release of cellular CPK and LDH. The parameters of I/R-induced regional tissue injury did not demonstrate any recovery and were not inhibited by TPL.     

Comparison of hind limb muscle mass in neonate and adult prosimian primates

Little ontogenetic data exist to indicate whether muscular organization of neonates reflects adult locomotion (e.g., leaping) or infant activities like clinging or the initial quadrupedal phase of locomotion that typifies most infant primates. In the present study, five species of primates with contrasting modes of locomotion were examined. Twenty-eight preserved neonatal and adult cadavers were studied by careful dissection of the hip, thigh, and leg muscles. Wet weights were taken of limb muscles after removal, and the muscles were combined into major functional groups (e.g., flexors, extensors) of each limb segment. Results demonstrate that the distribution of muscle mass within the thigh and within the leg are similar between neonates and adults for all species, with major groups varying by 5% or less in all but two age comparisons. Crural indices of the neonates are nearly identical to those of the adults, but leg/thigh muscle mass ratios were higher in the neonates. Species vary greatly in the percentage of adult limb segment muscle mass present in neonates, with Tarsius syrichta having the greatest percentage for all segments and two lemurids showing the least. These results primarily track differences in relative body mass at birth rather than developmental differences. The adaptive distribution of muscle, as discussed previously for adult prosimians, appears to be established at birth. Neonates of leaping species already have much larger quadriceps muscles than quadrupeds. Differences between large- and small-bodied leapers (e.g., pronounced superficial plantarflexor masses in tarsiers and pronounced deep plantarflexor masses in sifakas) also are present in neonates. Ratios of muscle mass over body mass are smaller in all neonates than in their adult counterparts, suggesting that the neonates are relatively poorly muscled, and that muscle mass must increase with positive allometry during growth.     

The effect of a unilateral muscle transplantation on the muscle fiber type and the MyHC isoform content in unoperated hind limb slow and fast muscles of the inbred Lewis rats

To reveal the effect of foreign innervation and altered thyroid status on fiber type composition and the myosin heavy chain (MyHC) isoform expression in the rat slow soleus (SOL) and fast extensor digitorum longus (EDL) muscles, a method of heterochronous isotransplantation was developed. In this experimental procedure, the SOL or EDL muscles of young inbred Lewis rats are grafted either into the host EDL or SOL muscles of adult rats of the same strain with normal or experimentally altered thyroid status. To estimate the extent of fiber type transitions in the transplanted muscles, the SOL and EDL muscle from the unoperated leg and unoperated muscles from the operated leg could be legitimately used as controls, but only when the experimental procedure itself does not affect these muscles. To verify this assumption, we have compared the fiber type composition and the MyHC isoform content of unoperated contralateral SOL and EDL muscles and ipsilateral unoperated SOL muscle of experimental rats after unilateral isotransplantation into the host EDL muscle with corresponding muscles of the naive rats of the same age and strain. We provide compelling evidence that the unilateral heterochronous isotransplantation has no significant effect on the fiber type composition and the MyHC isoform content of unoperated muscles of experimental animals. Hence, these muscles can be used as controls in our grafting experiments.     

The symmetry of the medial collateral and anterior cruciate ligament properties: a biochemical study in the rat hind limb

The medial collateral (MCL) and the anterior cruciate ligament (ACL) of the rat's knee are frequently used in biomedical research and occasionally in ligament healing studies. The contralateral normal ligament serves as a control. In this study the presence of symmetry in the biomechanical properties of the MCL and the ACL was investigated. Bilateral femur-MCL-tibia and femur-ACL-tibia preparations were obtained from the hind limbs of sixty rats and were subjected to tensile testing to failure under the same loading conditions. Tensile load to failure, stiffness and energy absorption capacity were measured and the mode of failure was recorded. All biomechanical parameters were not significantly different between the two knees of the same animal, although significant individual variation was evident. The most common mechanism of failure was mid-substance tear. Symmetry seems to exist in the biomechanical properties of the MCL and the ACL in the rat knee. When ligament healing is evaluated, increased group size is necessary and the use of a normal control group may be advisable. The contralateral normal knee ligament may serve as a control when the properties of an injured ligament are evaluated and when the parameters of tensile testing failure under similar load conditions are applied.     

The cat step cycle: hind limb joint angles and muscle lengths during unrestrained locomotion

The development of the polarity and bilateral asymmetry of the future adult zooid has been traced to their earliest morphological expression in the palleal bud of Botryllus. The account is based upon continued observation of living buds. The polarized antero-posterior and dorso-ventral axes are first expressed by the skewing of a symmetrical, hemispherical bud towards the anterior end of the parental bud. Identification of these axes is reinforced by the development of a loop-like blood circulation, the primary circulation, in the horizontal plane during the enlargement of the skewed hemisphere to form a stalked vesicle. Bilateral asymmetry is first expressed by the asymmetrical expansion of the vesicle stage. The right posterior corner of the vesicle expands further posteriorly and becomes more acute than the left posterior corner. This larger expansion persists throughout the development of the right atrial cavity, which finally expands across the mid-line to partially surround the gut. The bilateral asymmetry, expressed in the expanded vesicle, is reinforced by the development in sequence of a rounded gut rudiment and a pericardial rudiment in positions that would be expected from the asymmetry of the expanded vesicle. The first appearance of the gut rudiment occurs earlier than had been recognized previously. Conflicting accounts of the time and mode of formation of the pericardial rudiment have been clarified. The results of this study are discussed in the context of determination of bud territory, polarity and bilateral asymmetry.     

Acute gliclazide administration enhances glucose and ketone body utilization in the perfused hind limb of normal and streptozotocin-diabetic rats

Sulfonylureas are the most commonly used oral hypoglycemic agents. Their hypoglycemic actions are produced not only by stimulating insulin secretion but also by extrapancreatic mechanisms. Some groups have already demonstrated the extrapancreatic actions of sulfonylureas on carbohydrate metabolism in the liver, fat and muscle. In this study, we showed in an in situ perfused hind limb preparation of STZ-diabetic rats that gliclazide has an acute effect on ketone body and glucose utilization.     

The nifk gene is widely expressed in mouse tissues and is up-regulated in denervated hind limb muscle

Denervation of skeletal muscle alters the expression of many genes, which may be important for establishing optimal conditions for reinnervation. Using the differential display technique we have attempted to discover neurally regulated genes in skeletal muscle. An mRNA that is up-regulated in denervated hind limb muscle was identified and cloned. The cDNA encodes an RNA-binding protein, which was discovered during the course of this work to be a nucleolar protein interacting with the fork-head associated domain of the proliferation marker protein Ki-67, and named NIFK. We show that the nifk gene is widely expressed in adult mouse tissues and that the expression is up-regulated in denervated hind limb muscle. No difference between expression in perisynaptic and extrasynaptic portions of muscle was observed. The widespread expression in adult tissues suggests that the NIFK protein has other functions in addition to its interaction with Ki-67, which is only expressed in proliferating cells.     

The effect of different storage methods on the subsequent biochemical performance of perfused canine livers

Canine livers were stored in 4 different ways prior to an evaluation by a normothermic dilute blood test perfusion. The storage modalities were hypothermia alone, hypothermic low-flow perfusion with Tis-U-Sol, hypothermic low-flow perfusion with cryoprecipitated plasma and normothermic perfusion with dilute blood.     

The protective efficacy of magnolol in hind limb ischemia-reperfusion injury

We investigated the protective effects of magnolol, an active antioxidant and free radical scavenger extracted from Magnolia officinalis, in a hind limb ischemic-reperfusion animal model. Adult male Spraque-Dawley rats were subjected to hind limb ischemic insult for 2 hours and were intravenously treated with magnolol at 0.01 mg/kg (n=8), 0.3 mg/kg (n=8) mg/kg or 1 mg/kg (n=8) mg/kg, or vehicle (n=8). At 24 h post-insult, the levels of nitrite/nitrate (NOX), malondialdehyde (MDA) and myeloperoxidase (MPO), as well as the degree of muscle damage, were assessed. Relative to controls, animals treated with magnolol (0.3 and 1 mg/kg) had attenuated muscular inflammation, edema and damage. Magnolol (0.3–1 mg/kg) also effectively reduced postischemic rises in the MDA, NOx and MPO levels (p<0.05, respectively). Magnolol administrated at 0.01 mg/kg, however, failed to protect against the ischemic-perfusion limb injury. In addition, magnolol (0.01–1 mg/kg) did not affect local muscular blood reperfusion or other physiological parameters, including hematocrit, glucose, arterial blood gases and mean arterial blood pressure. Thus, intravenous administration with magnolol at 0.3–1 mg/kg protects against ischemic limb damage in rats. This cytoprotection may be attributed to its antioxidant, anti-nitrosative and anti-inflammatory actions.     

Temporal progress of muscle adaptation to endurance training in hind limb muscles of young rats

Summary The soleus, rectus femoris and gastrocnemius muscles of young rats were studied after 3, 6 and 12 weeks of treadmill training. The muscle fibers were characterized histochemically by their succinate dehydrogenase (SDH) and myofibrillar ATPase activity, and morphometrically by their cross-sectional areas, which were corrected for different body weights of control and trained animals.After 12 weeks of training the mean area of fibers in the muscles studied was not significantly different from the controls, as expected. In the soleus muscle the percentage of the fast-twitch fibers was decreased as a result of their transformation into slow-twitch fibers. Trained soleus muscles were the only muscles showing pathologically altered fibers, suggesting overload. The percentages of fiber types and their areas exhibited changes specific for the muscles and muscle regions studied.From these results it is concluded that the adaptation follows the sequence proportional adaptation of morphometrical parameters, disproportional adaptation of the areas of fiber types, and disproportional adaptation of the percentages and/or the areas of the fiber types. It is shown by comparison with the literature that this sequence may be generalized to a sequence of increasing expense necessary for the adaptation to increasing stimuli, and that the most decisive factors for adaptation are work load, frequency of exercise, period of training, and the age of the subject at the initiation of the training.