Variation in the uncoupling protein 2 and 3 genes and human performance

Uncoupling proteins 2 and 3 (UCP2 and UCP3) may negatively regulate mitochondrial ATP synthesis and, through this, influence human physical performance. However, human data relating to both these issues remain sparse. Examining the association of common variants in the UCP3/2 locus with performance phenotypes offers one means of investigation. The efficiency of skeletal muscle contraction, delta efficiency (DE), was assessed by cycle ergometry in 85 young, healthy, sedentary adults both before and after a period of endurance training. Of these, 58 were successfully genotyped for the UCP3-55C>T (rs1800849) and 61 for the UCP2-866G>A (rs659366) variant. At baseline, UCP genotype was unrelated to any physical characteristic, including DE. However, the UCP2-866G>A variant was independently and strongly associated with the DE response to physical training, with UCP2-866A allele carriers exhibiting a greater increase in DE with training (absolute change in DE of -0.2 ± 3.6% vs. 1.7 ± 2.8% vs. 2.3 ± 3.7% for GG vs. GA vs. AA, respectively; P = 0.02 for A allele carriers vs. GG homozygotes). In multivariate analysis, there was a significant interaction between UCP2-866G>A and UCP3-55C>T genotypes in determining changes in DE (adjusted R(2) = 0.137; P value for interaction = 0.003), which was independent of the effect of either single polymorphism or baseline characteristics. In conclusion, common genetic variation at the UCP3/2 gene locus is associated with training-related improvements in DE, an index of skeletal muscle performance. Such effects may be mediated through differences in the coupling of mitochondrial energy transduction in human skeletal muscle, but further mechanistic studies are required to delineate this potential role.

Genetics of muscle strength and power: polygenic profile similarity limits skeletal muscle performance

Environmental and genetic factors influence muscle function, resulting in large variations in phenotype between individuals. Multiple genetic variants (polygenic in nature) are thought to influence exercise-related phenotypes, yet how the relevant polymorphisms combine to influence muscular strength in individuals and populations is unclear. In this analysis, 22 genetic polymorphisms were identified in the literature that have been associated with muscular strength and power phenotypes. Using typical genotype frequencies, the probability of any given individual possessing an "optimal" polygenic profile was calculated as 0.0003% for the world population. Future identification of additional polymorphisms associated with muscular strength phenotypes would most likely reduce that probability even further. To examine the genetic potential for muscular strength within a human population, a "total genotype score" was generated for each individual within a hypothetical population of one million. The population expressed high similarity in polygenic profile with no individual differing by more than seven genotypes from a typical profile. Therefore, skeletal muscle strength potential within humans appears to be limited by polygenic profile similarity. Future research should aim to replicate more genotype-phenotype associations for muscular strength, because only five common genetic polymorphisms identified to date have positive replicated findings.

Protocols of in vitro protein covalent binding studies in liver

Xenobiotics, including therapeutic agents, can produce a variety of beneficial, as well as adverse, effects in mammals. One potential source of drug-mediated toxicity stems from metabolic activation of the parent compound, typically catalyzed by one or more members of the cytochrome P450 family of enzymes. The resulting electrophile, if not quenched by low molecular weight endogenous nucleophiles, can form covalent adducts to cellular proteins, potentially resulting in enzyme inactivation, cell death, or formation of an immunogenic species. The toxicological consequences of exposure to such reactive intermediates range from mild inflammation to organ failure, anaphylaxis, and death. At Merck Research Laboratories, the potential of drug candidates to bind covalently to proteins is evaluated at the lead optimization stage of drug discovery by incubating a radiolabeled analog of the compound in question with liver microsomal preparations (under oxidative conditions) or whole cells (full cellular metabolic capability), typically derived from rat and human liver. A semi-automated method based on the Brandel Harvester technique then is used to measure the formation of covalent adducts of the test compound to liver proteins. This assay is viewed as an important component of drug discovery programs, since the findings are employed to guide specific efforts to abrogate bioactivation issues through informed structural modification of lead compounds.

The effect of crank inertial load on the physiological and biomechanical responses of trained cyclists

The existing literature suggests that crank inertial load has little effect on the responses of untrained cyclists. However, it would be useful to be aware of any possible effect in the trained population, particularly considering the many laboratory-based studies that are conducted using relatively low-inertia ergometers. Ten competitive cyclists (mean VO(2max) = 62.7 ml x kg(-1) x min(-1), s = 6.1) attended the human performance laboratories at the University of Wolverhampton. Each cyclist completed two 7-min trials, at two separate inertial loads, in a counterbalanced order. The inertial loads used were 94.2 kg x m(2) (high-inertia trial) and 2.4 kg x m(2) (low-inertia trial). Several physiological and biomechanical measures were undertaken. There were no differences between inertial loads for mean peak torque, mean minimum torque, oxygen uptake, blood lactate concentration or perceived exertion. Several measures showed intra-individual variability with blood lactate concentration and mean minimum torque, demonstrating coefficients of variation > 10%. However, the results presented here are mostly consistent with previous work in suggesting that crank inertial load has little direct effect on either physiology or propulsion biomechanics during steady-state cycling, at least when cadence is controlled.

Metabolic activation of indole-containing prostaglandin D2 receptor 1 antagonists: Impacts of glutathione trapping and glucuronide conjugation on covalent binding

Some DP1 receptor antagonists from an indole-containing series were shown to cause in vitro covalent binding to protein in rat and human liver microsomes. Glutathione trapping experiments along with in vitro labeling assays confirmed that the presence of a strong electron withdrawing group was necessary to abrogate in vitro covalent binding, leading to the discovery of MK-0524. Hepatocyte incubations and in vivo studies showed that acyl-glucuronide formation did not translate into covalent binding.

Discovery of a Potent and Selective Prostaglandin D2 Receptor Antagonist, [(3R)-4-(4-Chloro- benzyl)-7-fluoro-5-(methylsulfonyl)-1,2,3,4-tetrahydrocyclopenta[b]indol-3-yl]-acetic Acid (MK-0524)

The discovery of the potent and selective prostaglandin D2 (PGD2) receptor (DP) antagonist [(3R)-4-(4-chlorobenzyl)-7-fluoro-5-(methylsulfonyl)-1,2,3,4-tetrahydrocyclopenta[b]indol-3-yl]-acetic acid (13) is presented. Initial lead antagonists 6 and 7 were found to be potent and selective DP antagonists (DP Ki = 2.0 nM for each); however, they both suffered from poor pharmacokinetic profiles, short half-lives and high clearance rates in rats. Rat bile duct cannulation studies revealed that high concentrations of parent drug were present in the biliary fluid (Cmax = 1100 microM for 6 and 3900 microM for 7). This pharmacokinetic liability was circumvented by replacing the 7-methylsulfone substituent present in 6 and 7 with a fluorine atom resulting in antagonists with diminished propensity for biliary excretion and with superior pharmacokinetic profiles. Further optimization led to the discovery of the potent and selective DP antagonist 13.

No correlation between circulating ACE activity and $$ {\user2{V}}{\mathbf{O}}_{{{\mathbf{2}}_{{{\mathbf{max}}}} }} $$ or mechanical efficiency in women

The insertion (I) variant of the angiotensin-1 converting enzyme (ACE) I/D genetic polymorphism is associated with lower circulating and tissue ACE activity. Some studies have also suggested associations of ACE I/D genotype with endurance phenotypes. This study assessed the relationships between circulating ACE activity, ACE I/D genotype, mechanical efficiency and the maximal rate of oxygen uptake in sedentary individuals. Sixty-two untrained women were tested for mechanical efficiency during submaximal cycle ergometry (delta and gross efficiencies during exercise between 40 and 80 W) and the maximal rate of oxygen uptake during incremental treadmill running. Respiratory variables were measured using indirect calorimetry. Venous blood was obtained for direct assay of circulating ACE activity, allowing for the assessment of correlations between two continuous variables, rather than a categorical analysis of endurance phenotype by genotype alone. ACE I/D genotype was also determined, and was strongly associated with circulating ACE activity (P < 0.0005). Neither circulating ACE activity (27.4 +/- 8.4 nM His-Leu-ml(-1)) nor ACE genotype showed a statistically significant association with any of the endurance phenotypes measured. The weak correlations observed included r = -0.122 (P = 0.229) for the relationship between delta efficiency (23.9 +/- 2.5%) and circulating ACE activity and r = 0.134 (P > 0.6) for the relationship between maximal aerobic power (149.1 +/- 22.9 ml kg(-2/3) min(-1)) and circulating ACE activity. The data do not support a role for systemic ACE activity in the regulation of endurance performance in sedentary individuals, extending this observation to a large female cohort.

A semi-automated method for measuring the potential for protein covalent binding in drug discovery

INTRODUCTION

Covalent protein binding of metabolically reactive intermediates of drugs has been implicated in drug toxicity including the occurrence of idiosyncratic drug toxicity. Investigators therefore would prefer to avoid developing compounds that produce significant amounts of reactive metabolites. By incubating the radiolabeled drug of interest with liver microsomes it is possible to evaluate the propensity of a drug candidate to covalently bind to proteins.

METHODS

Here we present a semi-automated method in which a Brandel cell harvester is used to collect and wash proteins that have been incubated with radiolabeled drug. This method utilizes glass fiber filter paper to capture precipitated protein, rather than the more traditional exhaustive extraction/centrifugation approach. Using model compounds (including [14C]diclofenac, [3H]imipramine, [14C]naphthalene, and [14C]L-746530) we compare the covalent binding results obtained using this method to results generated using the traditional method and we performed cross-laboratory testing of assay reproducibility.

RESULTS

It was found that results from new method correlated highly with the traditional method (R2=0.89). The cross-laboratory testing of the method showed an average interlaboratory coefficient of variation of only 18.4%.

DISCUSSION

This method provides comparable results to the more traditional centrifugation-based method with considerable time and labor savings.

Circulating angiotensin converting enzyme activity is correlated with muscle strength

PURPOSE

The D-variant of the angiotensin-1 converting enzyme (ACE) gene is associated with higher circulating and tissue ACE activity. Some studies have suggested a similar association of genotype with muscle strength or the gain in strength in response to training. This study has assessed the relationship between circulating ACE activity, strength, and the response to training.

METHODS

Eighty-one untrained men were tested for quadriceps muscle strength, and 44 of these performed an 8-wk program of dynamic strength training of the quadriceps muscle group. Venous blood was obtained for assessment of circulating ACE activity before and after the training program. ACE genotype was also determined.

RESULTS

At baseline, circulating ACE activity was significantly correlated with isometric (r = 0.25-0.29, P < 0.02) and isokinetic (r = 0.38, P < 0.0005) quadriceps muscle strength. ACE genotype also seemed to be related to pretraining muscle strength. However, circulating ACE activity showed no significant association with the 9-14% mean increases of muscle strength in response to the training intervention. ACE genotype also showed no association with the training-induced change in muscle strength. Circulating ACE activity did not change significantly after the training program.

CONCLUSIONS

The data support a role for ACE in the regulation of human skeletal muscle strength, but do not confirm a role in altering the response to short-term training.

USE OF A BENZYLOXY-SUBSTITUTED LACTONE CYCLOOXYGENASE-2 INHIBITOR AS A SELECTIVE FLUORESCENT PROBE FOR CYP3A ACTIVITY IN PRIMARY CULTURED RAT AND HUMAN HEPATOCYTES

Previously, we have shown that the inhibition of the transporter-mediated hepatic uptake of cerivastatin (CER) by cyclosporin A (CsA) could, at least partly, explain a pharmacokinetic interaction between these drugs in humans. In the present study, we have examined the effect of CsA on the in vivo disposition of CER in rats and the in vitro uptake of [14C]CER in isolated rat hepatocytes in an attempt to evaluate the effect of inhibition of transporter-mediated hepatic uptake on the in vivo CER disposition. The steady-state plasma concentration of CER increased 1.4-fold when coadministered with CsA up to a steady-state blood concentration of 4 microM. Studies of [14C]CER uptake into isolated rat hepatocytes showed saturable transport, with the saturable portion accounting for more than 80% of the total uptake. CsA competitively inhibited the uptake of [14C]CER with a Ki of 0.3 microM. The IC50 for the uptake of [14C]CER in the absence and presence of rat plasma was 0.2 and 2.3 microM, respectively. The in vivo hepatic uptake of [14C]CER evaluated by the liver uptake index method was also inhibited by CsA in a dose-dependent manner. On the other hand, CsA did not inhibit the metabolism of [14C]CER in rat microsomes. The in vitro and in vivo correlation analysis revealed that this pharmacokinetic interaction between these drugs in rats could be quantitatively explained by the inhibition of transporter-mediated hepatic uptake. Thus, this drug-drug interaction in rats is predominantly caused by the transporter-mediated uptake process.

The acute effects of exercise and glucose ingestion on circulating angiotensin-converting enzyme in humans

Angiotensin-converting enzyme (ACE) activity has been suggested as a determinant of some exercise phenotypes via some studies that have associated the ACE gene with exercise performance, although several studies provide conflicting evidence regarding the influence of the ACE gene. The relationships between ACE phenotype (ACE activity) and various exercise parameters should also be examined. An early step in this process is to determine whether common environmental stimuli such as exercise and diet have acute effects on ACE activity. In this study, the acute effects of aerobic exercise, resistance exercise and glucose ingestion on circulating ACE activity were examined. On three separate occasions, 20 healthy adult volunteers (9 female and 11 male) performed 20 min of submaximal cycle exercise at 70-80% of maximal heart rate, four sets of ten repetitions of unilateral leg extension resistance exercise at ten-repetition maximum load, or ingested 1 g kg(-1) glucose. Circulating ACE activity was assessed for 1 h after each intervention using a modified fluorometric method. Pre-intervention ACE activity remained remarkably stable across test days (difference < or =1.8%). Furthermore, there was no significant change in circulating ACE activity following any of the interventions (difference from pre-intervention values < or =6.8% when unadjusted for plasma volume changes, < or =4.5% when adjusted for plasma volume changes). These results suggest that acute exercise and glucose ingestion interventions as used here do not affect circulating ACE activity. These findings are an early step in illuminating the relationships between ACE activity and various exercise parameters.

Bradykinin receptor gene variant and human physical performance

Accumulating evidence suggests that athletic performance is strongly influenced by genetic variation. One such locus of influence is the gene for angiotensin-I converting enzyme (ACE), which exhibits a common variant [ACE insertion (I)/deletion (D)]. ACE can drive formation of vasoconstrictor ANG II but preferentially degrades vasodilator bradykinin. The ACE I allele is associated with higher kinin activity. A common gene variant in the kinin β2 receptor (B2R) exists: the -9 as opposed to +9 allele is associated with higher receptor mRNA expression. We tested whether this variant was associated with the efficiency of muscular contraction [delta efficiency (DE)] in 115 healthy men and women, or with running distance among 81 Olympic standard track athletes. We further sought evidence of biological interaction with ACE I/D genotype. DE was highly significantly associated with B2R genotype (23.84 ± 2.41 vs. 24.25 ± 2.81 vs. 26.05 ± 2.26% for those of +9/+9 vs. +9/-9 vs. -9/-9 genotype; n = 25, 61, and 29, respectively; P = 0.0008 for ANOVA adjusted for sex). There was evidence for interaction with ACE I/D genotype, with individuals who were ACE II, with B2R -9/-9 having the highest DE at baseline. The ACE I/B2R -9 “high kinin receptor activity” haplotype was significantly associated with endurance (predominantly aerobic) event among elite athletes ( P = 0.003). These data suggest that common genetic variation in the B2R is associated with efficiency of skeletal muscle contraction and with distance event of elite track athletes and that at least part of the associations of ACE and fitness phenotypes is through elevation of kinin activity.

Bioactive constituents of the roots of Cynanchum atratum

A novel biphenylneolignan, 2,6,2',6'-tetramethoxy-4,4'-bis(2,3-epoxy-1-hydroxypropyl)biphenyl (1), and two new glycosides named atratoglaucosides A (2) and B (3), were isolated from the roots of Cynanchum atratum, and their structures were determined on the basis of chemical and spectroscopic evidence. The aglycons of 2 and 3 were identified as glaucogenin C and 7-desoxyneocynapanogenin A, a new disecopregnane. A known compound, glaucogenin C 3-O-beta-D-cymaropyranosyl-(1-->4)-alpha-L-diginopyranosyl-(1-->4)-beta-D-thevetopyranoside (4), isolated from the same source, showed a significant cytotoxic effect against 212 cells. This substance also gave a significant inhibitory effect on TNF-alpha (tumor necrosis factor-alpha) formation from the RAW 264.7 mouse macrophage-like cell line stimulated with LPS (lipopolysaccharide) and on the N9 microglial cell line stimulated with LPS/IFN-gamma (interferon-gamma).

New lignan glycosides with potent antiinflammatory effect, isolated from Justicia ciliata

Two new lignan glycosides, 4-O-[alpha-L-arabinopyranosyl-(1' "-->2' ')-beta-D-xylopyranosyl-(1' " '-->5' ')-beta-D-apiofuranosyl]diphyllin (1), named ciliatoside A (1), and 4-O-¿[beta-D-apiofuranosyl-(1' " "-->3' ")-alpha-L-arabinopyranosyl-(1' "-->2' ')][beta-D-xylopyranosyl-(1' " '-->5' ')]-beta-D-apiofuranosyl¿diphyllin (2), named ciliatoside B (2), were isolated from the whole plant of Justicia ciliata. The structures of 1 and 2 were determined by spectral and chemical methods. Compounds 1 and 2 strongly inhibited the accumulation of NO(2)(-) in lipopolysaccharide-stimulated RAW 264.7 cells in a concentration-dependent manner with IC(50) values of 27.1 +/- 1.6 and 29.4 +/- 1.4 microM, respectively.

Cytotoxic lignans of Justicia ciliata

Two new naturally occurring 1-aryl-2,3-naphthalide lignans, cilinaphthalide A (1) and cilinaphthalide B (2), and nine known compounds were isolated from the whole plant of Justicia ciliata. Their structures were established by spectral analysis, and their cytotoxic activity was evaluated against several different cell lines. The known compound, justicidin A, showed potent cytotoxic effects against T-24, CaSki, SiHa, HT-3, PLC/PRF/5, and 212 cells in vitro.

Induction of cytochrome-P450 in cryopreserved rat and human hepatocytes

Our laboratory has been routinely using suspended and cultured human hepatocytes for predicting drug metabolism and enzyme induction by drug candidates to aid drug discovery. Increasing limitation and irregular availability of human tissue has indicated the need for maximizing the use of this valuable resource. Cryopreservation of surplus hepatocytes after isolation would greatly increase the potential of this model. However, cryopreservation of hepatocytes by various methods has resulted in cells with poor metabolic activity and unacceptably low survival rates in culture. Recently, Zaleski et al. (Biochem. Pharmacol. 46 (1993) 111-116) reported that cryopreserved rat hepatocytes retained metabolic capacity similar to fresh hepatocytes when the cells were preincubated for 30 min at 37 degrees C in Krebs Ringer bicarbonate buffer prior to freezing. To further explore this methodology, both the functional capacity of the cells in culture as well as their ability to retain CYP inducibility were investigated with thawed cryopreserved hepatocytes. Although human hepatocytes were used in this study the initial work focused on rat hepatocytes as a cell model. Our results showed that while the preincubation step did not appear to effect the initial viability of cryopreserved hepatocytes, survival of the cells in culture was greatly enhanced. Plating efficiencies for nonpreincubated cryopreserved hepatocytes were decreased to approximately 15% of fresh cells after 48 h in culture. In contrast, cells that had been preincubated prior to freezing had an excellent plating efficiency (approximately 60%) and responded to classical CYP inducers dexamethasone, beta-naphthoflavone and phenobarbital in a manner indistinguishable from that of fresh hepatocytes. Experiments with human hepatocytes have also demonstrated similar results. This is the first time to our knowledge that cryopreserved hepatocytes from both rat and human have been shown to reproducibly respond to CYP inducers in culture.

Molecular flexibility profiling using NMR spectroscopy

Molecular flexibility is a factor that is not extensively studied in most pharmaceutical research efforts. When it is, the level of effort is high involving the preparation of detailed models supported by either molecular dynamics simulations and/or Nuclear Magnetic Resonance data. While these studies are both powerful and illuminating, they cannot be routinely applied in a drug discovery setting as they are time and expertise intensive. Yet there seems to be little doubt that at least in some cases, molecular flexibility plays a key role in complex formation. A simple, rapid and generally applicable flexibility profiling protocol was applied to two model systems and data describing the internal mobility of carbon atoms were obtained. The protocol utilizes the Model Free approach and NMR data to characterize the internal molecular dynamics of these compounds. The first model system consisted of fluorene and diphenylmethane where the anticipated flexibility trends were observed in the data providing a link between chemical intuition and the experimental results. Data on a second model system, which consisted of two Paclitaxel analogs, showed predictable patterns including dynamical phenyl and methyl groups and a relatively immobile taxane core. Subtle differences in the internal dynamics within the taxane core suggest that it cannot be considered as a rigid structure. Key advantages of using this approach are that no prior knowledge or supposition of dynamical features is required, the protocol can be carried out in most medicinal chemistry laboratories and the data obtained provide a common, empirically derived reference point to discuss the effects of molecular flexibility on activity.

Cryopreservation of rat and human liver slices by rapid freezing

The cryopreservation of human liver slices is a promising way to enhance the ability to test the metabolism of drug candidates. This study demonstrates the use of a novel technique for the cryopreservation of both rat and human liver slices. In this technique the slices are treated with Me2SO and sandwiched between aluminum plates separated by a thin gasket. The device is then submerged in liquid nitrogen to freeze the slices, which can then be stored until use. To thaw the slices, the apparatus is submerged in a water bath at 37 degrees C. Slices frozen and thawed in this manner were compared to those frozen in conventional cryovials. The viability of the slices was determined by incubating them in 12-well plates and measuring urea synthesis, ethoxycoumarin metabolism, and cytosolic enzyme leakage (LDH and ALT). The viability of rat slices frozen between plates approached that of fresh slices and was consistently higher than slices frozen in cryovials. Slices from two human samples gave similar results. The technique was found to work over a wide range of Me2SO concentrations (4.5 to 22% was tested) with an optimal concentration between 10 and 15%.

Ophthalmology's future in the next decade: a historical and comparative perspective

PURPOSE

To gain a historical and comparative perspective about the future of ophthalmology within the profession of medicine.

METHODS

A literature search is made of disciplines other than medicine (history, sociology, philosophy, economics, and ethics) in order to assess factors responsible for survival and healthiness of a profession. The "learned" professions (medicine, law, and theology) are assessed. Other "professional" careers valued by society (sports and classical music) are reviewed.

RESULTS

From the perspective of other disciplines, the future of ophthalmology is seen as vulnerable and fragile. Survival of professions, be they classically or economically defined, is linked to societal needs, a profession's unique commitment and ability to provide services to society, and the profession's maintenance of knowledge as well as skill-based services. Historical evidence has shown erosion of a profession's power consequent to capitalist influences, government influences, access of skills by less trained individuals, and elitist posturing by a profession. Comparative evidence has shown societal acceptance of an escalation of salaries for designated superstars, increasing roles and influence of managerial personnel, and trivialization of values other than economic ones.

CONCLUSION

Attention to historical and comparative trends by individual ophthalmologists as well as associations representing ophthalmologists is mandatory if ophthalmology as we know it is to survive within the profession of medicine.

Manipulation of knee extensor force using percutaneous electrical myostimulation during eccentric actions: effects on indices of muscle damage in humans

Percutaneous electrical myostimulation (PES) was used to manipulate the force produced by the knee extensor muscles during eccentric exercise, thereby providing a model to investigate the role of force in muscle damage. Two eccentric exercise bouts of equal work were performed by nine subjects, using fixed voltage PES at 20 Hz (to produce moderate muscle forces) and 100 Hz (to produce high muscle forces). Muscle contractility, serum creatine kinase activity (CK) and muscle soreness (MS) were evaluated before, and up to 14 days after exercise. Data are presented as means+/-SEM, and were analysed using repeated measures analysis of variance (ANOVA), t-tests and Wilcoxon tests. Peak forces were higher during the 100 Hz bout than the 20 Hz bout for repetitions 1 (472+/-60 vs 237+/-23 Newtons), 10 (381+/-26 vs 233+/-26 Newtons), 20 (310+/-24 vs 218+/-24 Newtons), all p < 0.01, t-test and 30 (297+/-27 vs 204+/-21 Newtons), p < 0.05, t-test. Following the 100 Hz bout, maximum voluntary contractile force (MVC) was lower (p<0.01, ANOVA), and CK was higher (p<0.0001, ANOVA) than after the 20 Hz bout. Subjects also reported greater MS on days 2 to 6 (p<0.05, Wilcoxon test) following the 100 Hz bout. Despite a decline in the stimulated 20:100 Hz tetanic force ratio after each bout (p<0.01, ANOVA) there was no difference between bouts (p>0.05, ANOVA). The higher rise in CK and MS after the 100 Hz bout, together with the greater deficit in MVC, suggest that in humans, muscle force is a contributing factor to muscle injury during eccentric actions.

Electromyogram activity and mean power frequency in exercise-damaged human muscle

Eight volunteers performed two bouts of 50 voluntary maximal eccentric contractions of the knee extensors of one leg 3 weeks apart. During maximal voluntary isometric contractions performed at intervals after each bout, electromyogram (EMG) mean power frequency declined after bout one (P < 0.01 Duncan's test), whereas integrated EMG did not change after either bout. These results suggest that unaccustomed eccentric contractions produce a temporary reduction in mean muscle activation frequency during subsequent maximal isometric contractions.

The effect of severe eccentric exercise-induced muscle damage on plasma elastase, glutamine and zinc concentrations

The aim of this study was to determine if severe exercise-induced muscle damage alters the plasma concentrations of glutamine and zinc. Changes in plasma concentrations of glutamine, zinc and polymorphonuclear elastase (an index of phagocytic cell activation) were examined for up to 10 days following eccentric exercise of the knee extensors of one leg in eight untrained subjects. The exercise bout consisted of 20 repetitions of electrically stimulated eccentric muscle actions on an isokinetic dynamometer. Subjects experienced severe muscle soreness and large increases in plasma creatine kinase activity indicative of muscle fibre damage. Peak soreness occurred at 2 days post-exercise and peak creatine kinase activity [21714 (6416) U x l(-1) mean (SEM)] occurred at 3 days post-exercise (P < 0.01 compared with pre-exercise). Plasma elastase concentration was increased at 3 days post-exercise compared with pre-exercise (P < 0.05), and is presumably indicative of ongoing phagocytic leucocyte infiltration and activation in the damaged muscles. There were no significant changes in plasma zinc and glutamine concentrations in the days following eccentric exercise. We conclude that exercise-induced muscle damage does not produce changes in plasma glutamine or zinc concentrations despite evidence of phagocytic neutrophil activation.