共查询到20条相似文献,搜索用时 328 毫秒
1.
Thomas D. O’Brien Neil D. Reeves Vasilios Baltzopoulos David A. Jones Constantinos N. Maganaris 《Journal of biomechanics》2010,43(6):1190-1195
It is not currently known how the mechanical properties of human tendons change with maturation in the two sexes. To address this, the stiffness and Young's modulus of the patellar tendon were measured in men, women, boys and girls (each group, n=10). Patellar tendon force (Fpt) was calculated from the measured joint moment during a ramped voluntary isometric knee extension contraction, the antagonist knee extensor muscle co-activation quantified from its electromyographical activity, and the patellar tendon moment arm measured from magnetic resonance images. Tendon elongation was imaged using the sagittal-plane ultrasound scans throughout the contraction. Tendon cross-sectional area was measured at rest from ultrasound scans in the transverse plane. Maximal Fpt and tendon elongation were (mean±SE) 5453±307 N and 5±0.5 mm for men, 3877±307 N and 4.9±0.6 mm for women, 2017±170 N and 6.2±0.5 mm for boys and 2169±182 N and 5.9±0.7 mm for girls. In all groups, tendon stiffness and Young's modulus were examined at the level that corresponded to the maximal 30% of the weakest participant's Fpt and stress, respectively; these were 925–1321 N and 11.5–16.5 MPa, respectively. Stiffness was 94% greater in men than boys and 84% greater in women than girls (p<0.01), with no differences between men and women, or boys and girls (men 1076±87 N/mm; women 1030±139 N/mm; boys 555±71 N/mm and girls 561.5±57.4 N/mm). Young's modulus was 99% greater in men than boys (p<0.01), and 66% greater in women than girls (p<0.05). There were no differences in modulus between men and women, or boys and girls (men 597±49 MPa; women 549±70 MPa; boys 255±42 MPa and girls 302±33 MPa). These findings indicate that the mechanical stiffness of tendon increases with maturation due to an increased Young's modulus and, in females due to a greater increase in tendon cross-sectional area than tendon length. 相似文献
2.
《Journal of electromyography and kinesiology》2014,24(3):375-379
The objectives of this study was to investigate the acute effects of various magnitudes of tendon strain on the mechanical properties of the human medial gastrocnemius (MG) in vivo during controlled heel-drop exercises. Seven male and seven female volunteers performed two different exercises executed one month apart: one was a heel-drop exercise on a block (HDB), and the other was a heel-drop exercise on level floor (HDL). In each regimen, the subjects completed a session of 150 heel-drop exercises (15 repetitions × 10 sets; with a 30 s rest following each set). Before and immediately after the heel-drop exercise, the ankle plantar flexor torque and elongation of the MG were measured using a combined measurement system of dynamometry and ultrasonography and then the MG tendon strain and stiffness were evaluated in each subject. The tendon stiffness measured prior to the exercises was not significantly different between the two groups 23.7 ± 10.6 N/mm and 24.1 ± 10.0 N/mm for the HDB and HDL, respectively (p > .05). During the heel-drop exercise, it was found that the tendon strain during the heel-drop exercise on a block (8.4 ± 3.7%) was significantly higher than the strain measured on the level floor (5.4 ± 3.8%) (p < .05). In addition, the tendon stiffness following the heel-drop exercise on a block (32.3 ± 12.2 N/mm) was significantly greater than the tendon stiffness measured following the heel-drop exercise on the level floor (25.4 ± 11.4 N/mm) (p < .05). The results of this study suggest that tendon stiffness immediately following a heel-drop exercise depends on the magnitude of tendon strain. 相似文献
3.
4.
François Hug Paul W. Hodges Kylie J. Tucker 《Journal of electromyography and kinesiology》2013,23(6):1413-1420
IntroductionWe aimed to determine whether the changes in muscle activity (in terms of both gross electromyography (EMG) and motor unit (MU) discharge characteristics) observed during pain are spatially organized with respect to pain location within a muscle which is the main contributor of the task.MethodsSurface and fine-wire EMG was recorded during matched low-force isometric plantarflexion from soleus (from four quadrants with fine-wire EMG and from the medial/lateral sides with surface EMG), both gastrocnemii heads, peroneus longus, and tibialis anterior. Four conditions were tested: two control conditions that each preceded contractions with pain induced in either the lateral (PainL) or medial (PainM) side of soleus.ResultsNeither the presence (p = 0.28) nor location (p = 0.19) of pain significantly altered gross muscle activity of any location (lateral/medial side of soleus, gastrocnemii, peroneus longus and tibialis anterior). Group data from 196 MUs show redistribution of MU activity throughout the four quadrants of soleus, irrespective of pain location. The significant decrease of MU discharge rate during pain (p < 0.0001; PainL: 7.3 ± 0.9–6.9 ± 1.1 Hz, PainM: 7.0 ± 1.1 to 6.6 ± 1.1 Hz) was similar for all quadrants of the soleus (p = 0.43), regardless of the pain location (p = 0.98). There was large inter-participant variation in respect to the characteristics of the altered MU discharge with pain.ConclusionResults from both surface and fine-wire EMG recordings do not support the hypothesis that muscle activity is reorganized in a simple systematic manner with respect to pain location. 相似文献
5.
Harri Piitulainen Alberto Botter Roberto Merletti Janne Avela 《Journal of electromyography and kinesiology》2013,23(2):302-310
Motor unit behavior differs between contraction types at submaximal contraction levels, however is challenging to study during maximal voluntary contractions (MVCs). With multi-channel surface electromyography (sEMG), mean physiological characteristics of the active motor units can be extracted. Two 8-electrode sEMG arrays were attached on biceps brachii muscle (one on each head) to examine behavior of sEMG variables during isometric, eccentric and concentric MVCs of elbow flexors in 36 volunteers.On average, isometric (364 ± 88 N) and eccentric (353 ± 74 N) MVCs were higher than concentric (290 ± 73 N) MVC (p < 0.001). Mean muscle fiber conduction velocity (CV) was highest during eccentric MVC (4.42 ± 0.49 m/s) than concentric (4.25 ± 0.49 m/s, p < 0.01) and isometric (4.14 ± 0.45 m/s, p < 0.001) MVCs. Furthermore, eccentric MVC showed lower sEMG amplitude at the largest elbow joint angles (120–170°) and higher CV at the smallest (70–150°) elbow joint angles (p < 0.05–0.001) than concentric MVC.The differences in CV and sEMG amplitude between the MVCs suggest that the control strategy of motor units differs between the contraction types during MVCs, and is dependent on the muscle length between the dynamic MVCs. 相似文献
6.
Xu Pang Zhen-Dong Cao Jiang-Lan Peng Shi-Jian Fu 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2010,155(2):253-258
To test whether the effects of feeding on swimming performance vary with acclimation temperature in juvenile southern catfish (Silurus meridionalis), we investigated the specific dynamic action (SDA) and swimming performance of fasting and feeding fish at acclimation temperatures of 15, 21, 27, and 33 °C. Feeding had no effect on the critical swimming speeding (Ucrit) of fish acclimated at 15 °C (p = 0.66), whereas it elicited a 12.04, 18.70, and 20.98% decrease in Ucrit for fish acclimated at 21, 27 and 33 °C, respectively (p < 0.05). Both the maximal postprandial oxygen consumption rate (VO2peak) and the active metabolic rate (VO2active, maximal aerobic sustainable metabolic rate of fasting fish) increased significantly with temperature (p < 0.05). The postprandial maximum oxygen consumption rates during swimming (VO2max) were higher than the VO2active of fasting fish at all temperature groups (p < 0.05). The VO2max increased with increasing temperature, but the relative residual metabolic scope (VO2max? VO2peak) during swimming decreased with increasing in temperature. The present study showed that the impairment of postprandial swimming performance increased with increasing temperature due to the unparalleled changes in the catfish's central cardio-respiratory, peripheral digestive and locomotory capacities. The different metabolic strategies of juvenile southern catfish at different temperatures may relate to changes in oxygen demand, imbalances in ion fluxes and dissolved oxygen levels with changes in temperature. 相似文献
7.
J. Greig Inglis Rene Vandenboom David A. Gabriel 《Journal of electromyography and kinesiology》2013,23(6):1289-1294
Sex-differences in the maximum rate of torque development (dτ/dtmax) may be due to differences in maximum muscle strength, because higher torque values mathematically lead to higher values for the rate of change in torque. The rate of change in the isometric torque-time curve is often normalized to the isometric maximum voluntary contraction (MVC) to evaluate males and females on a relative scale. Normalization eliminates sex-differences in dτ/dtmax in the lower limbs because males and females are more comparable (i.e., differences between the sexes are relatively small) with respect to both muscle size and strength. However, normalization fails to result in parody in dτ/dtmax of the upper limb, leading to the idea that other factors may be involved. This study determined if sex-differences in dτ/dtmax in the upper limb can be attributed to differences in isometric MVC and/or a neural variable related to rate of increase in muscle activation (Q30). Forty-six participants (23 males, 23 females) performed maximal isometric elbow flexion contractions, “as hard and as fast as possible”. Maximum torque (τmax), dτ/dtmax, and the rate of increase in surface electromyographic (sEMG) activity (Q30) were assessed. Muscle plus bone cross-sectional area (M + B CSA) of the upper arm was calculated to estimate differences in muscle size, only for comparative purposes. Maximum strength (55.5%) and muscle size (41.9%) of the elbow flexors in males were much greater than that of females (p < 0.05). There was a large difference (61.2%) between males and females with respect to dτ/dtmax that was reduced by statistical correction using an analysis of covariance (ANCOVA). The percent differences were reduced to 36.7% (p < 0.05) for τmax and 54.4% (p < 0.05) for Q30, but was nearly eliminated to 13.8% (p > 0.05) when both variables were used simultaneously as covariates. Since sex-differences in the upper limb dτ/dtmax persist, additional neural or biomechanical factors may be involved. 相似文献
8.
M. Rosa Bernal-López Ainhoa Rípodas Paloma Aragoncillo Amparo Carbonell Juan José Rufilanchas Raquel Fernández-Durango Francisco J. Tinahones Ricardo Gómez-Huelgas Arturo Fernández-Cruz 《Process Biochemistry》2009,44(6):661-667
Endothelin (ET) is a potent vasoconstrictor peptide implicated in numerous human diseases, including ischemic cardiomyopathy (ICM). ET binds to receptors ETA and ETB. Specific ET receptors were characterized in left atria of patients with end-stage heart failure due to ischemic cardiomyopathy (ICM) (n = 9) and healthy controls (n = 9). Saturation assays revealed a Kd and Bmax of 28 ± 8 pM and 87 ± 22 fmol mg?1 of protein, respectively, from healthy atria and 50 ± 9 pM and 162 ± 19 fmol mg?1 of protein, respectively, from diseased atria (p < 0.05). For competition studies, we obtained a percentage of ETA receptors using BQ123, 55% ± 5 and 66% ± 4 in healthy and diseased atria, respectively (p < 0.05). The percentage of ETB using BQ3020 was 55% ± 14 in healthy and 59% ± 10 in diseased atria. Microautoradiography studies showed a greater number of ET receptors, predominately ETA, existed in the myocardial layer of diseased atria compared with healthy atria. The percentage of occupied area was greater in the endocardium than the epicardium in diseased atria. These results showed an increase in the ETA/ETB receptor system in the failing human heart compared with the non-failing human heart. 相似文献
9.
Renfang Song Melissa Spera Colleen Garrett Ihor V. Yosypiv 《Mechanisms of development》2010,127(1-2):21-27
The renin-angiotensin system (RAS) plays a critical role in ureteric bud (UB) and kidney morphogenesis. Mutations in the genes encoding components of the RAS cause a spectrum of congenital abnormalities of the kidney and urinary tract (CAKUT). However, the mechanisms by which aberrations in the RAS result in CAKUT are poorly understood. Given that c-Ret receptor tyrosine kinase (RTK) is a major inducer of UB branching, the present study tested the hypothesis that angiotensin (Ang) II-induced activation of c-Ret plays a critical role in UB branching morphogenesis. E12.5 mice metanephroi were grown for 24 h in the presence or absence of Ang II, Ang II AT1 receptor (AT1R) antagonist candesartan, phosphatidylinositol 3-kinase (PI3 K) inhibitor LY294002 or ERK1/2 inhibitor PD98059. Ang II increased the number of UB tips (61 ± 2.4 vs. 45 ± 4.3, p < 0.05) compared with control. Quantitative RT-PCR analysis demonstrated that Ang II increased c-Ret mRNA levels in the kidney (1.35 ± 0.05 vs. 1.0 ± 0, p < 0.01) and in the UB cells (1.28 ± 0.04 vs. 1.0 ± 0, p < 0.01) compared to control. This was accompanied by increased Tyr1062Ret phosphorylation by Ang II (5.5 ± 0.9 vs. 1.8 ± 0.4 relative units, p < 0.05). In addition, treatment of UB cells with Ang II (10?5 M) increased phosphorylation of Akt compared to control (213 ± 16 vs. 100 ± 20%, p < 0.05). In contrast, treatment of metanephroi or UB cells with candesartan decreased c-Ret mRNA levels (0.72 ± 0.06 vs. 1.0 ± 0, p < 0.01; 0.68 ± 0.07 vs. 1.0 ± 0, p < 0.05, respectively) compared with control. Ang II-induced UB branching was abrogated by LY294002 (24 ± 2.6 vs. 37 ± 3.0, p < 0.05) or PD98059 (33 ± 2.0 vs. 48 ± 2.2, p < 0.01). These data demonstrate that Ang II-induced UB branching depends on activation of Akt and ERK1/2. We conclude that cross-talk between the RAS and c-Ret signaling plays an important role in the development of the renal collecting system. 相似文献
10.
The purpose of this study was to quantify strain and elongation of the long head of the biceps femoris (BFlh) and the semitendinosus (ST) tendon/aponeurosis. Forty participants performed passive knee extension trials from 90° of knee flexion to full extension (0°) followed by ramp isometric contractions of the knee flexors at 0°, 45° and 90° of knee flexion. Two ultrasound probes were used to visualize the displacement of BFlh and ST tendon/aponeurosis. Three-way analysis of variance designs indicated that: (a) Tendon/aponeurosis (passive) elongation and strain were higher for the BFlh than the ST as the knee was passively extended (p < 0.05), (b) contraction at each angular position was accompanied by a smaller BFlh tendon/aponeurosis (active) strain and elongation than the ST at higher levels of effort (p < 0.05) and (c) combined (passive and active) strain was significantly higher for the BFlh than ST during ramp contraction at 0° but the opposite was observed for the 45° and 90° flexion angle tests (p < 0.05). Passive elongation of tendon/aponeurosis has an important effect on the tendon/aponeurosis behavior of the hamstrings and may contribute to a different loading of muscle fibers and tendinous tissue between BFlh and ST. 相似文献
11.
Chiara Zoppirolli Hans-Christer Holmberg Barbara Pellegrini Diego Quaglia Lorenzo Bortolan Federico Schena 《Journal of electromyography and kinesiology》2013,23(6):1512-1519
This investigation was designed to evaluate the effectiveness of stretch–shortening cycling (SSCEFF) in upper-limb extensor muscles while cross-country skiing using the double-poling technique (DP). To this end, SSCEFF was analyzed in relation to DP velocity and performance. Eleven elite cross-country skiers performed an incremental test to determine maximal DP velocity (Vmax). Thereafter, cycle characteristics, elbow joint kinematics and poling forces were monitored on a treadmill while skiing at two sub-maximal and racing velocity (85% of Vmax). The average EMG activities of the triceps brachii and latissimus dorsi muscles were determined during the flexion and extension sub-phases of the poling cycle (EMGFLEX, EMGEXT), as well as prior to pole plant (EMGPRE). SSCEFF was defined as the ratio of aEMGFLEX to aEMGEXT. EMGPRE and EMGFLEX increased with velocity for both muscles (P < 0.01), as did SSCEFF (from 0.9 ± 0.3 to 1.3 ± 0.5 for the triceps brachii and from 0.9 ± 0.4 to 1.5 ± 0.5 for the latissimus dorsi) and poling force (from 253 ± 33 to 290 ± 36 N; P < 0.05). Furthermore, SSCEFF was positively correlated to Vmax, to EMGPRE and EMGFLEX (P < 0.05). The neuromuscular adaptations made at higher velocities, when more poling force must be applied to the ground, exert a major influence on the DP performance of elite cross-country skiers. 相似文献
12.
Rodrigo Carregaro Rafael Cunha Carlos Gomes Oliveira Lee E. Brown Martim Bottaro 《Journal of electromyography and kinesiology》2013,23(5):1090-1096
PurposePreload of antagonist muscles can be achieved by reciprocal actions (RAs) or by opposing muscle actions. However, evidence concerning neuromuscular and fatigue responses are scarce.ObjectiveTo compare the effects of different knee flexor (KF) preload methods on knee extension (KE) vastus medialis muscle fatigue, based on EMG-spectral index (FI), load range (LR), total work (TW), blood lactate (LAC) and biceps femoris co-activation (BFc) during resistance exercise.MethodsTwenty-four healthy men (23.5 ± 3.6 yrs) performed three antagonist pre-load isokinetic exercises (4 sets, 10 repetitions, 60° s?1, 1 min rest between sets): RA (KF contraction immediately followed by KE); Superset (SS; one KF set immediately followed by one KE set); Multiple Set (MS; four KF sets followed by four KE sets).ResultsTotal work was significantly greater in RA. There was no significant decrease in LR between sets in RA. The BFc did not differ between protocols (p = 0.063). However, RA presented greater biceps femoriscoactivation. The FI was greater during SS compared to RA and MS (p < 0.05). The SS had greater LAC when compared to MS and RA (p = 0.005 and p = 0.007, respectively).ConclusionIt is suggested that the RA protocol is more neuromuscular and metabolic efficient during the performance of knee extension resistance exercise. 相似文献
13.
H.A.M. Mutsaers M.J.G. Wilmer D. Reijnders J. Jansen P.H.H. van den Broek M. Forkink E. Schepers G. Glorieux R. Vanholder L.P. van den Heuvel J.G. Hoenderop R. Masereeuw 《生物化学与生物物理学报:疾病的分子基础》2013,1832(1):142-150
During chronic kidney disease (CKD), drug metabolism is affected leading to changes in drug disposition. Furthermore, there is a progressive accumulation of uremic retention solutes due to impaired renal clearance. Here, we investigated whether uremic toxins can influence the metabolic functionality of human conditionally immortalized renal proximal tubule epithelial cells (ciPTEC) with the focus on UDP-glucuronosyltransferases (UGTs) and mitochondrial activity. Our results showed that ciPTEC express a wide variety of metabolic enzymes, including UGTs. These enzymes were functionally active as demonstrated by the glucuronidation of 7-hydroxycoumarin (7-OHC; Km of 12 ± 2 μM and a Vmax of 76 ± 3 pmol/min/mg) and p-cresol (Km of 33 ± 13 μM and a Vmax of 266 ± 25 pmol/min/mg). Furthermore, a wide variety of uremic toxins, including indole-3-acetic acid, indoxyl sulfate, phenylacetic acid and kynurenic acid, reduced 7-OHC glucuronidation with more than 30% as compared with controls (p < 0.05), whereas UGT1A and UGT2B protein expressions remained unaltered. In addition, our results showed that several uremic toxins inhibited mitochondrial succinate dehydrogenase (i.e. complex II) activity with more than 20% as compared with controls (p < 0.05). Moreover, indole-3-acetic acid decreased the reserve capacity of the electron transport system with 18% (p < 0.03). In conclusion, this study shows that multiple uremic toxins inhibit UGT activity and mitochondrial activity in ciPTEC, thereby affecting the metabolic capacity of the kidney during CKD. This may have a significant impact on drug and uremic retention solute disposition in CKD patients. 相似文献
14.
C. Merlin F. Cachin A. Kelly D. Mestas D. De Freitas J. Maublant 《Médecine Nucléaire》2008,32(6):332-338
Purpose. – To evaluate the value of 18F-fluoro-2-désoxyglucose (FDG) PET-CT and maximal standardized uptake value (SUVmax) of the primary tumor for lymph node staging in cervical cancer.Materials and methods. – This retrospective study involved a series of 18 consecutive patients who had benefited from PET-CT and MRI at initial staging for a stage IB or higher cervical carcinoma. The SUVmax of each primary tumor was measured retrospectively. All patients had been previously treated by radiochemotherapy. Lymph node status was obtained in 12 of 18 cases.Results. – The sensitivity and specificity for determining lymph node status was 80 and 86%, respectively, for PET-CT, and 80 and 71% for MRI. In 16.6% of cases, PET-CT revealed unknown sus-diaphragmatic lesions. SUVmax of the primary tumor was significantly higher in the N+ than in the N− group (15.6 ± 1.6 vs 8.5 ± 3.9, p < 0.01). The optimal threshold was determined to be 10.8 from ROC analysis.Conclusion. – When staging with FDG PET-CT, SUVmax of a primary cervical cancer seems to be a good predictor of lymph node status. This could lead to an intensification of treatment for patients whose SUVmax is higher than 10.8. A prospective study would allow to assess a potential benefit of treatment intensification for patients with SUVmax higher than 10.8. 相似文献
15.
《Journal of electromyography and kinesiology》2014,24(5):762-769
The aim of this preliminary study was to examine the validity of a recently-introduced tool (MyotonPRO) for the assessment of mechanical parameters of the main lower extremity muscles in patients with chronic stroke. Thigh and shank muscles of 20 stroke patients with limited hypertonia (11 men and 9 women; mean age: 52 ± 11 yrs) and 20 healthy controls (11 men and 9 women; mean age: 53 ± 10 yrs) were bilaterally evaluated with (i) MyotonPRO for muscle stiffness, tone and elasticity, (ii) ultrasonography for muscle and subcutaneous thickness, and (iii) dynamometry for isometric muscle strength. MyotonPRO parameters of stroke patients were reassessed a week later (inter-day test-retest design). For all the investigated muscles, MyotonPRO variables did not differ between the more affected and the less affected side of patients (P > 0.05 for main side effect), and neither differed between patients and controls (P > 0.05 for main group effect), except for gastrocnemius medialis stiffness that was higher in patients (300 ± 51 N/m) than in controls (281 ± 29 N/m; P < 0.05). Thigh muscle stiffness was negatively correlated to subcutaneous thickness (r = −0.84 for the vastus lateralis; P < 0.001), while only tibialis anterior stiffness and tone correlated positively with muscle thickness (both r = 0.46; P < 0.01). Test-retest reliability of MyotonPRO parameters was adequate, except for muscle elasticity. The validity of MyotonPRO for the evaluation of thigh muscles in chronic stroke patients is partially challenged by the poor discriminant ability and by the considerable impact of subcutaneous tissue thickness (sex-dependent) on mechanical parameters. The potential validity of MyotonPRO for the assessment of shank muscles requires further investigation. 相似文献
16.
PurposeThis study evaluated whether RapidPlan based plans (RP plans) created by a single optimization, are usable in volumetric modulated arc therapy (VMAT) for patients with prostate cancer.MethodsWe used 51 previously administered VMAT plans to train a RP model. Thirty RP plans were created by a single optimization without planner intervention during optimization. Differences between RP plans and clinical manual optimization (CMO) plans created by an experienced planner for the same patients were analyzed (Wilcoxon tests) in terms of homogeneity index (HI), conformation number (CN), D95%, and D2% to planning target volume (PTV), mean dose, V50Gy, V70Gy, V75Gy, and V78Gy to rectum and bladder, monitor unit (MU), and multi-leaf collimator (MLC) sequence complexity.ResultsRP and CMO values for PTV D95%, PTV D2%, HI, and CN were significantly similar (p < 0.05 for all). RP mean dose, V50Gy, and V70Gy to rectum were superior or comparable to CMO values; RP V75Gy and V78Gy were higher than in CMO plans (p < 0.05). RP bladder dose-volume parameter values (except V78Gy) were lower than in CMO plans (p < 0.05). MU values were RP: 730 ± 55 MU and CMO: 580 ± 37 MU (p < 0.05); and MLC sequence complexity scores were RP: 0.25 ± 0.02 and CMO: 0.35 ± 0.03 (p < 0.05).ConclusionsRP plans created by a single optimization were clinically acceptable in VMAT for patient with prostate cancer. Our simple model could reduce optimization time, independently of planner’s skill and knowledge. 相似文献
17.
Filip J. Larsen Eddie Weitzberg Jon O. Lundberg Björn Ekblom 《Free radical biology & medicine》2010,48(2):342-347
The anion nitrate—abundant in our diet—has recently emerged as a major pool of nitric oxide (NO) synthase-independent NO production. Nitrate is reduced stepwise in vivo to nitrite and then NO and possibly other bioactive nitrogen oxides. This reductive pathway is enhanced during low oxygen tension and acidosis. A recent study shows a reduction in oxygen consumption during submaximal exercise attributable to dietary nitrate. We went on to study the effects of dietary nitrate on various physiological and biochemical parameters during maximal exercise. Nine healthy, nonsmoking volunteers (age 30 ± 2.3 years, VO2max 3.72 ± 0.33 L/min) participated in this study, which had a randomized, double-blind crossover design. Subjects received dietary supplementation with sodium nitrate (0.1 mmol/kg/day) or placebo (NaCl) for 2 days before the test. This dose corresponds to the amount found in 100–300 g of a nitrate-rich vegetable such as spinach or beetroot. The maximal exercise tests consisted of an incremental exercise to exhaustion with combined arm and leg cranking on two separate ergometers. Dietary nitrate reduced VO2max from 3.72 ± 0.33 to 3.62 ± 0.31 L/min, P < 0.05. Despite the reduction in VO2max the time to exhaustion trended to an increase after nitrate supplementation (524 ± 31 vs 563 ± 30 s, P = 0.13). There was a correlation between the change in time to exhaustion and the change in VO2max (R2 = 0.47, P = 0.04). A moderate dietary dose of nitrate significantly reduces VO2max during maximal exercise using a large active muscle mass. This reduction occurred with a trend toward increased time to exhaustion implying that two separate mechanisms are involved: one that reduces VO2max and another that improves the energetic function of the working muscles. 相似文献
18.
《Saudi Journal of Biological Sciences》2015,22(5):543-550
Oreochromis niloticus, weighing 36.45 ± 1.12 g were exposed to 10%, 20% and 30% of the LC50 of CdCl2 which represents treatments (T1)1.68, (T2)3.36 and (T3)5.03 mg/l, respectively, for a period of 10, 20 and 30 days. It was found that, compared to a control group reading of 0.19 ± 0.03 μg/g dry weight, accumulation of Cd in the gills was significantly (p < 0.05) increased in samples ranging between 7.64 ± 0.86 and 61.73 ± 0.82 μg/g dry weight from T1 at 10 days to T3 at 30 days. The accumulation of Cd in the liver, meanwhile, was also observed to significantly increase (p < 0.05) with increasing time and concentrations with results ranging between 3.21 ± 0.12 and 181.61 ± 1.32 compared to the control group results of 0.29 ± 0.04 μg/g dry weight. Although muscles exhibited lower levels of accumulation than the gills and liver they still showed the same pattern of increase compared to the control group, with a significant difference ranging between 0.32 ± 0.02 and 2.16 ± 0.08 compared to the control group results of 0.03 ± 0.001 μg/g dry weight. Also, haematological parameters such as red blood cells (RBCs), haemoglobin (Hb) and haematocrit (Hct) were reduced in fish exposed to Cd at all periods, with significant differences (p < 0.05). Plasma glucose concentration showed a significant increase. Total protein levels of fish showed a significant reduction (p > 0.05) for all exposed treatments. Also, the total lipid level increased significantly as fish were exposed to increasing cadmium concentrations, compared to control fish. Finally, the activities of aspartate aminotransferase (AST IU/l) and alanine aminotransferase (ALT IU/l) showed a significant increase (p < 0.05) with increasing time and concentrations. 相似文献
19.
Cristina Ballester Benjamín Sarriá Eduardo García-Granero Manuel Mata Javier Milara Esteban J. Morcillo Salvador Lledó Julio Cortijo 《Life sciences》2010,86(9-10):358-364
AimsIn this study, responses of β3-adrenoceptor agonists were examined on human isolated internal anal sphincter (IAS) in order to explore their relaxant effects on hypertonicity of IAS.Main methodsThe relaxant efficacy (Emax) and potency (? logIC50) of BRL37344 and SR58611A, β3-adrenoceptor agonists, were examined in contracted IAS muscle strips. The presence of β3-adrenoceptors, and changes in intracellular calcium and cyclic nucleotide levels in IAS muscle were tested by Western blotting, epifluorescence microscopy and enzyme immunoassay, respectively.Key findingsBRL37344 and SR58611A relaxed contracted IAS muscle (Emax = 27 ± 3% and 35 ± 3%; -logIC50 = 6.26 ± 0.24 and 4.87 ± 0.13; respectively). These relaxant responses were blocked by SR59230A, a selective β3-antagonist but not by β1/β2-selective antagonists, neuronal inhibitor or inhibition of nitric oxide synthase. The Emax of β3-agonists was similar to that of β2-selective agonists but smaller than that of isoprenaline (nonselective agonist) or β1-selective agonists. BRL37344 (100 μM) increased cAMP (1.5-fold) without cGMP change, and depressed intracellular calcium signal. β3-Adrenoceptor expression was smaller than that of β1- and β2-adrenoceptors.SignificanceThis is the first study demonstrating the presence of β3-adrenoceptor in human IAS muscle and β3-mediated relaxation of augmented sphincter tone. However, direct β3-relaxation appears smaller than that obtained for nonselective agonists which may limit their potential use in the treatment of anorectal hypertonicity disorders. 相似文献
20.
Ismael León-Rivera Gumersindo Mirón-López Samuel Estrada-Soto Francisco Aguirre-Crespo María del Carmen Gutiérrez Gloria María Molina-Salinas Gerardo Hurtado Gabriel Navarrete-Vázquez Elizur Montiel 《Bioorganic & medicinal chemistry letters》2009,19(16):4652-4656
Tyrianthins A (1) and B (2), two new partially acylated glycolipid ester-type heterodimers were isolated from Ipomoea tyrianthina. Scammonic acid A was determined as the glycosidic acid in both monomeric units. Tyrianthin A (1) (IC50 0.24 ± 0.09 μM and Emax 81.80 ± 0.98%), and tyrianthin B (2) (IC50 0.14 ± 0.08 μM and Emax 87.68 ± 0.72%) showed significant in vitro relaxant effect on aortic rat rings, in endothelium- and concentration-dependent manners. Also, these compounds were able to increase the release of GABA and glutamic acid in brain cortex, and displayed weak antimycobacterial activity. 相似文献