Use of the dried blood spot sampling process coupled with fast gas chromatography and negative-ion chemical ionization tandem mass spectrometry: application to fluoxetine, norfluoxetine, reboxetine, and paroxetine analysis.

The objective of this work was to combine the advantages of the dried blood spot (DBS) sampling process with the highly sensitive and selective negative-ion chemical ionization tandem mass spectrometry (NICI-MS-MS) to analyze for recent antidepressants including fluoxetine, norfluoxetine, reboxetine, and paroxetine from micro whole blood samples (i.e., 10 microL). Before analysis, DBS samples were punched out, and antidepressants were simultaneously extracted and derivatized in a single step by use of pentafluoropropionic acid anhydride and 0.02% triethylamine in butyl chloride for 30 min at 60 degrees C under ultrasonication. Derivatives were then separated on a gas chromatograph coupled with a triple-quadrupole mass spectrometer operating in negative selected reaction monitoring mode for a total run time of 5 min. To establish the validity of the method, trueness, precision, and selectivity were determined on the basis of the guidelines of the "Société Française des Sciences et des Techniques Pharmaceutiques" (SFSTP). The assay was found to be linear in the concentration ranges 1 to 500 ng mL(-1) for fluoxetine and norfluoxetine and 20 to 500 ng mL(-1) for reboxetine and paroxetine. Despite the small sampling volume, the limit of detection was estimated at 20 pg mL(-1) for all the analytes. The stability of DBS was also evaluated at -20 degrees C, 4 degrees C, 25 degrees C, and 40 degrees C for up to 30 days. Furthermore, the method was successfully applied to a pharmacokinetic investigation performed on a healthy volunteer after oral administration of a single 40-mg dose of fluoxetine. Thus, this validated DBS method combines an extractive-derivative single step with a fast and sensitive GC-NICI-MS-MS technique. Using microliter blood samples, this procedure offers a patient-friendly tool in many biomedical fields such as checking treatment adherence, therapeutic drug monitoring, toxicological analyses, or pharmacokinetic studies.

ß2-adrenergic agonists actions on the human skeletal muscle

Les ß2-agonistes sont des bronchodilatateurs qui sont prescrits pour traiter l'asthme et l'asthme induite par l'exercice (AIE). Il est relevant de comprendre s'il y a une utilisation adéquate de ces médicaments pour traiter l'AIE chez les athlètes de haut niveau, ou s'ils sont utilisés pour leur potentiel effet ergogénique sur la performance physique. Ce travail examine les actions centrales et périphériques sur la fonction contractile du muscle squelettique humain in vivo induits par l'ingestion d'une dose thérapeutique de ß2- agonistes. Le premier but était d'évaluer si les ß2-agonistes exerçaient une potentialisation de la contractilité du muscle humain et/ou un effet "anti¬fatigue" comme observé dans le modèle animal. Les résultats n'ont fournit aucune évidence d'une potentialisation sur le muscle squelettique humain in vivo non-fatigué et fatigué induit par l'administration orale de ß2-agonistes. Tout effet excitateur exercé par ce traitement sur le système nerveux central a été aussi exclu. Le deuxième but était de déterminer si les ß2-agonistes affaiblissaient la contractilité du muscle squelettique humain à contraction lente, et d'évaluer si ce changement pouvait interférer avec le contrôle moteur au muscle. Les résultats ont montré que les ß2-agonistes affaiblissent la contractilité des fibres lentes, comme conséquence de l'effet lusitrope positif se produisant dans ces fibres. La capacité de développer une force maximale n'est pas réduite par le traitement, même si une augmentation de la commande centrale au muscle est requise pour produire la même force lors de contractions sous-maximales. Le but final était d'examiner si une adaptation du contrôle moteur était re¬quis pour compenser l'affaiblissement des fibres lentes exercée par les ß2- agonistes pendant un exercice volontaire, et de déterminer si cette adaptation centrale pouvait accroître la fatigue musculaire. Malgré le fait que les résultats confirment l'effet affaiblissant induit par les ß2-agonistes, ce changement contractile n'influence pas le contrôle moteur au muscle pendant les contractions sous-maximales de l'exercice fatiguant, et n'accroît pas le degré de fatigue. Ce travail éclaircit les actions spécifiques des ß2-agonistes sur la fonction contractile du muscle squelettique humain in vivo et leurs influence sur le contrôle moteur. Les mécanismes sous-jacents de l'action ergogénique sur la performance physique produit par les ß2-agonistes sont aussi élucidés. -- ß2-Agonists are bronchodilators that are widely prescribed for the treatment of asthma and exercise-induced asthma (EIA). The extensive use of ß2-agonists by competitive athletes has raised the question as to whether there is a valid need for this class of drugs because of EIA or a misuse because of their potential ergogenic effect on exercise performance. This work investigated the central and peripheral actions that were elicited by the ingestion of a therapeutic dose of ß2-agonists on the contractility of human skeletal muscle in vivo. The first objective was to investigate whether ß2-agonists would potentiate muscle contractility and/or exert the "anti-fatigue" effect observed in animal models. The findings did not provide any evidence for the ß2-agonist-induced potentiation of in vivo human non-fatigued and fatigued skeletal muscle. Moreover, the findings exclude any excitatory action of this treatment on the central nervous system. The second objective was to explore whether the weakening action on the contractile function would occur after ß2-agonist intake in human slow-twitch skeletal muscle and to ascertain whether this contractile change may interfere with muscle motor control. The results showed that ß2-agonists weaken the contractility of slow-twitch muscle fibres as a result of the lusitropic effect occurring in these fibres. The maximal force-generating capacity of the skeletal muscle is not reduced by ß2-agonists, even though an augmented neural drive to muscle is required to develop the same force during submaximal contractions. The final objective was to examine whether a motor control adjustment is needed to compensate for the ß2-agonist-induced weakening effect on slow- twitch fibres during a voluntary exercise and to also assess whether this central adaptation could exaggerate muscle fatigue. Despite the findings confirming the occurrence of the weakening action that is exerted by ß2- agonists, this contractile change did not interfere with muscle motor control during the submaximal contractions of the fatiguing exercise and did not augment the degree of the muscle fatigue. This work contributes to a better understanding of the specific actions of ß2-agonists on the contractile function of in vivo human skeletal muscles and their influence on motor control. In addition, the findings elucidate mechanisms that could underlie the ergogenic effect that is exerted by ß2- agonists on physical performance.

Methyl and ethyl chloride synthesis in microreactors

Methyl chloride is an important chemical intermediate with a variety of applications. It is produced today in large units and shipped to the endusers. Most of the derived products are harmless, as silicones, butyl rubber and methyl cellulose. However, methyl chloride is highly toxic and flammable. On-site production in the required quantities is desirable to reduce the risks involved in transportation and storage. Ethyl chloride is a smaller-scale chemical intermediate that is mainly used in the production of cellulose derivatives. Thus, the combination of onsite production of methyl and ethyl chloride is attractive for the cellulose processing industry, e.g. current and future biorefineries. Both alkyl chlorides can be produced by hydrochlorination of the corresponding alcohol, ethanol or methanol. Microreactors are attractive for the on-site production as the reactions are very fast and involve toxic chemicals. In microreactors, the diffusion limitations can be suppressed and the process safety can be improved. The modular setup of microreactors is flexible to adjust the production capacity as needed. Although methyl and ethyl chloride are important chemical intermediates, the literature available on potential catalysts and reaction kinetics is limited. Thus the thesis includes an extensive catalyst screening and characterization, along with kinetic studies and engineering the hydrochlorination process in microreactors. A range of zeolite and alumina based catalysts, neat and impregnated with ZnCl2, were screened for the methanol hydrochlorination. The influence of zinc loading, support, zinc precursor and pH was investigated. The catalysts were characterized with FTIR, TEM, XPS, nitrogen physisorption, XRD and EDX to identify the relationship between the catalyst characteristics and the activity and selectivity in the methyl chloride synthesis. The acidic properties of the catalyst were strongly influenced upon the ZnCl2 modification. In both cases, alumina and zeolite supports, zinc reacted to a certain amount with specific surface sites, which resulted in a decrease of strong and medium Brønsted and Lewis acid sites and the formation of zinc-based weak Lewis acid sites. The latter are highly active and selective in methanol hydrochlorination. Along with the molecular zinc sites, bulk zinc species are present on the support material. Zinc modified zeolite catalysts exhibited the highest activity also at low temperatures (ca 200 °C), however, showing deactivation with time-onstream. Zn/H-ZSM-5 zeolite catalysts had a higher stability than ZnCl2 modified H-Beta and they could be regenerated by burning the coke in air at 400 °C. Neat alumina and zinc modified alumina catalysts were active and selective at 300 °C and higher temperatures. However, zeolite catalysts can be suitable for methyl chloride synthesis at lower temperatures, i.e. 200 °C. Neat γ-alumina was found to be the most stable catalyst when coated in a microreactor channel and it was thus used as the catalyst for systematic kinetic studies in the microreactor. A binder-free and reproducible catalyst coating technique was developed. The uniformity, thickness and stability of the coatings were extensively characterized by SEM, confocal microscopy and EDX analysis. A stable coating could be obtained by thermally pretreating the microreactor platelets and ball milling the alumina to obtain a small particle size. Slurry aging and slow drying improved the coating uniformity. Methyl chloride synthesis from methanol and hydrochloric acid was performed in an alumina-coated microreactor. Conversions from 4% to 83% were achieved in the investigated temperature range of 280-340 °C. This demonstrated that the reaction is fast enough to be successfully performed in a microreactor system. The performance of the microreactor was compared with a tubular fixed bed reactor. The results obtained with both reactors were comparable, but the microreactor allows a rapid catalytic screening with low consumption of chemicals. As a complete conversion of methanol could not be reached in a single microreactor, a second microreactor was coupled in series. A maximum conversion of 97.6 % and a selectivity of 98.8 % were reached at 340°C, which is close to the calculated values at a thermodynamic equilibrium. A kinetic model based on kinetic experiments and thermodynamic calculations was developed. The model was based on a Langmuir Hinshelwood-type mechanism and a plug flow model for the microreactor. The influence of the reactant adsorption on the catalyst surface was investigated by performing transient experiments and comparing different kinetic models. The obtained activation energy for methyl chloride was ca. two fold higher than the previously published, indicating diffusion limitations in the previous studies. A detailed modeling of the diffusion in the porous catalyst layer revealed that severe diffusion limitations occur starting from catalyst coating thicknesses of 50 μm. At a catalyst coating thickness of ca 15 μm as in the microreactor, the conditions of intrinsic kinetics prevail. Ethanol hydrochlorination was performed successfully in the microreactor system. The reaction temperature was 240-340°C. An almost complete conversion of ethanol was achieved at 340°C. The product distribution was broader than for methanol hydrochlorination. Ethylene, diethyl ether and acetaldehyde were detected as by-products, ethylene being the most dominant by-product. A kinetic model including a thorough thermodynamic analysis was developed and the influence of adsorbed HCl on the reaction rate of ethanol dehydration reactions was demonstrated. The separation of methyl chloride using condensers was investigated. The proposed microreactor-condenser concept enables the production of methyl chloride with a high purity of 99%.

A comparative study of aging of the elastic fiber system of the diaphragm and the rectus abdominis muscles in rats

In the present study the age-related changes of the striated muscle elastic fiber system were investigated in the diaphragm and rectus abdominis muscles of 1-, 4-, 8- and 18-month-old rats. The activation patterns of these muscles differ in that the diaphragm is regularly mobilized tens of times every minute during the entire life of the animal whereas the rectus abdominis, although mobilized in respiration, is much less and more irregularly activated. The elastic fibers were stained by the Verhoeff technique for mature elastic fibers. Weigert stain was used to stain mature and elaunin elastic fibers, and Weigert-oxone to stain mature, elaunin and oxytalan elastic fibers. The density of mature and elaunin elastic fibers showed a progressive increase with age, whereas the amount of oxytalan elastic fibers decreased in both diaphragm and rectus abdominis muscles and their muscular fascias. These age-related quantitative and structural changes of the elastic fiber system may reduce the viscoelastic properties of the diaphragm and rectus abdominis muscles, which may compromise the transmission of tensile muscle strength to the tendons and may affect maximum total strength.

Impact of mass lumping on gravity and Rossby waves in 2D finite-element shallow-water models

The goal of this study is to evaluate the effect of mass lumping on the dispersion properties of four finite-element velocity/surface-elevation pairs that are used to approximate the linear shallow-water equations. For each pair, the dispersion relation, obtained using the mass lumping technique, is computed and analysed for both gravity and Rossby waves. The dispersion relations are compared with those obtained for the consistent schemes (without lumping) and the continuous case. The P0-P1, RT0 and P-P1 pairs are shown to preserve good dispersive properties when the mass matrix is lumped. Test problems to simulate fast gravity and slow Rossby waves are in good agreement with the analytical results.

Magnetic cloud distortion resulting from propagation through a structured solar wind: Models and observations

Numerical simulations of magnetic clouds (MCs) propagating through a structured solar wind suggest that MC-associated magnetic flux ropes are highly distorted by inhomogeneities in the ambient medium. In particular, a solar wind configuration of fast wind from high latitudes and slow wind at low latitudes, common at periods close to solar minimum, should distort the cross section of magnetic clouds into concave-outward structures. This phenomenon has been reported in observations of shock front orientations, but not in the body of magnetic clouds. In this study an analytical magnetic cloud model based upon a kinematically distorted flux rope is modified to simulate propagation through a structured medium. This new model is then used to identify specific time series signatures of the resulting concave-outward flux ropes. In situ observations of three well studied magnetic clouds are examined with comparison to the model, but the expected concave-outward signatures are not present. Indeed, the observations are better described by the convex-outward flux rope model. This may be due to a sharp latitudinal transition from fast to slow wind, resulting in a globally concave-outward flux rope, but with convex-outward signatures on a local scale.

Classification-based probabilistic modeling of texture transition for fast line search tracking and delineation

We introduce a classification-based approach to finding occluding texture boundaries. The classifier is composed of a set of weak learners, which operate on image intensity discriminative features that are defined on small patches and are fast to compute. A database that is designed to simulate digitized occluding contours of textured objects in natural images is used to train the weak learners. The trained classifier score is then used to obtain a probabilistic model for the presence of texture transitions, which can readily be used for line search texture boundary detection in the direction normal to an initial boundary estimate. This method is fast and therefore suitable for real-time and interactive applications. It works as a robust estimator, which requires a ribbon-like search region and can handle complex texture structures without requiring a large number of observations. We demonstrate results both in the context of interactive 2D delineation and of fast 3D tracking and compare its performance with other existing methods for line search boundary detection.

CHANGES OF GENE EXPRESSION IN ELECTRICALLY STIMULATED AND CONTRALATERAL RAT SOLEUS MUSCLES

In this study we investigate the effect of a single session of high-intensity contractions on expression of pleiotropic genes and, in particular, those genes associated with metabolism in soleus muscle from electrically stimulated (ES) and contralateral (CL) limbs. The right limbs of male Wistar rats were submitted to contractions by 200-ms trains of electrical stimulation at 100-Hz frequency with pulses of 0.1 ms (voltage 24 3 V) delivered each second for 1 hour. Soleus muscles were isolated 1 hour after contraction, and gene expression was analyzed by a macroarray technique (Atlas Toxicology 1.2 Array; Clontech Laboratories). Electrical stimulation increased expression in 92 genes (16% of the genes present in the membrane). Sixty-six genes were upregulated in both ES and CL soleus muscles, and expression of 26 genes was upregulated in the ES muscle only. The most altered genes were those related to stress response and metabolism. Electrical stimulation also raised expression of transcription factors, translation and posttranslational modification of proteins, ribosomal proteins, and intracellular transducers/effectors/modulators. The results indicate that a single session of electrical stimulation upregulated expression of genes related to metabolism and oxidative stress in soleus muscle from both ES and CL limbs. These findings may indicate an association with tissue hypertrophy and metabolic adaptations induced by physical exercise training not only in the ES but also in the CL non-stimulated muscle, suggesting a cross-education phenomenon. Muscle Nerve 40: 838-846, 2009

Effect of neuromuscular electrical stimulation and isotonic exercises in flexor and extensor muscles of knee of hemiplegic patients

Aim. To verify the muscular force and resistance to the movement of the flexor and extensor muscles of the knee of patients with spasticity after treatment with neuromuscular electrical stimulation (NMES) and isotonic exercises. Patients and methods. The patients this study were divided into group I (NMES) and group 2 (isotonic exercises). Their muscular torque and resistance to the movement of the flexor and extensor knee muscles were measured by the isokinetic dynamometer and the degree of spasticity by the modified Ashworth scale before and after ten sessions. Results. Alterations in the scores of the modified Ashworth scale were not observed. An increase in the flexor torque in group 1 (p = 0.041) and in group 2 (p = 0.001) was verified. In the passive mode, group 1 presented a reduction of resistance to the flexion movement (p = 0.026), while in group 2, a reduction of resistance to both the flexion (p = 0,029) and extension movements (p = 0.019) was verified. Conclusions. The two therapeutical resources had their efficiency proven only for the increase of the force of the flexor muscles. The resistance to movement, the isotonic exercises were more effective because they promoted a reduction in the resistance of the flexor and extensor knee muscles.

Thermal history versus sedimentary history: OSL sensitivity of quartz grains extracted from rocks and sediments

The optically stimulated luminescence (OSL) sensitivity of quartz has a significant influence on luminescence dating procedures. Furthermore, identifying the natural controls of quartz OSL sensitivity is an important step towards new applications of OSL in geology such as provenance tracing. We evaluate the OSL sensitivity (total and the proportion of the informally assigned fast, medium and slow components) of single grains of quartz extracted from 10 different igneous and metamorphic rocks with known formation conditions; and from fluvial and coastal sediments with different sedimentary histories and known source rocks. This sample suite allows assessment of the variability of the OSL sensitivity of single quartz grains with respect to their primary origin and sedimentary history. We observed significant variability in the OSL sensitivity of grains within all studied rock and sediment samples, with the brightest grains of each sample being those dominated by the fast component. Quartz from rocks formed under high temperature (> 500 degrees C) conditions, such as rhyolites and metamorphic rocks from the amphibolite facies, display higher OSL sensitivity. The OSL sensitivity of fluvial sediments which have experienced only a short transport distance is relatively low. These sediments show a small increase in OSL sensitivity downstream, mainly due to a decreasing fraction of ""dim"" grains. The quartz grains from coastal sands present very high sensitivity and variability, which is consistent with their long sedimentary history. The high variability of the OSL sensitivity of quartz from coastal sands is attributed more to the mixture of grains with distinct sedimentary histories than to the provenance from many types of source rocks. The temperature of crystallization and the number of cycles of burial and solar exposure are suggested as the main natural factors controlling the OSL sensitivity of quartz grains. The increase in OSL sensitivity due to cycles of erosion and deposition surpasses the sensitivity inherited from the source rock, with this increase being mainly related to the sensitization of fast OSL components. The discrimination of grains with different sedimentary histories through their OSL sensitivities can allow the development of quantitative provenance methods based on quartz. (C) 2010 Elsevier B.V. All rights reserved.

Amazonian Vegetable Oils and Fats: Fast Typification and Quality Control via Triacylglycerol (TAG) Profiles from Dry Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) Mass Spectrometry Fingerprinting

Amazonian oils and fats display unique triacylglycerol (TAG) profiles and, because of their economic importance as renewable raw materials and use by the cosmetic and food industries, are often subject to adulteration and forgery. Representative samples of these oils (andiroba, Brazil nut, buriti, and passion fruit) and fats (cupuacu, murumuru, and ucuba) were characterized without pre-separation or derivatization via dry (solvent-free) matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Characteristic profiles of TAG were obtained for each oil and tat. Dry MALDI-TOF MS provides typification and direct and detailed information, via TAG profiles, of their variable combinations of fatty acids. A database from spectra could be developed and may be used for their fast and reliable typification, application screening, and quality control.

Electromyographic analysis of the masseter and buccinator muscles with the Pro-Fono Facial Exerciser use in bruxers

The aim of this study was to evaluate the efficiency of the Pro-Fono Facial Exerciser (Pro-Fono Productos Especializaclos para Fonoaudiologia Ltda.., Barueri/SP, Brazil) to decrease bruxism, as well as the correlation between the masseter and the buccinator muscles using electromyography (EMG). In this study, 39 individuals ranging from 23 to 48 years of age were selected from a dental school and then underwent surface EMG at three different periods of time: 0, 10, and 70 days. They were divided into a normal control group, a bruxer control group (without device), and an experimental bruxer group who used the device. The bruxer group showed a greater masseter EMG amplitude when compared to the normal group, while the experimental group had deceased activity with a reduction in symptoms. The buccinator EMG spectral analysis of the experimental bruxist group showed asynchronous contractions of the masseter muscle (during jaw opening) after using the Pr6-Fono Facial Exerciser. The normal group also showed asynchronous contractions. Upon correlation of the data between these muscles, the inference is that there is a reduction in bruxism when activating the buccinator muscle.

Caracterização das fibras musculares do músculo Semitendinosus de bezerros mestiços Angus-Nelore recebendo somatotropina bovina recombinante (rbST) até a desmama

Objetivando-se estudar o efeito da somatotropina bovina recombinante (rbST) sobre a freqüência de distribuição e o diâmetro das fibras musculares do músculo Semitendinosus, 36 bezerros mestiços ½Angus-Nelore, com idade inicial de 63 ± 17 dias e pesando 76,8 ± 14,7 kg, criados em pastagem de Brachiaria decumbens e suplementados em creep feeding, foram submetidos a dois tratamentos até a desmama (217 dias): 18 bezerros receberam 1,4 mg/kg de rbST (Boostin®) a cada 14 dias e 18 receberam solução salina (controle). As amostras de músculo foram coletadas aos 117 (biópsia) e aos 217 dias de idade, quando foram abatidos cinco animais por tratamento. Os animais suplementados apresentaram maior diâmetro para as fibras do tipo glicolítica de contração rápida (FG) aos 117 dias e tendência de aumento aos 217 dias e não diferiram em relação ao grupo controle quanto ao diâmetro das fibras oxidativas-glicolíticas de contração rápida (FOG) e oxidativas de contração lenta (SO) e à frequência de FG, FOG e SO aos 117 e 217 dias de idade. Independentemente da aplicação de rbST, houve significativo aumento do diâmetro das fibras SO e FOG, tendência de aumento de diâmetro das fibras FG, maior frequência de SO e redução da frequência de FG entre 117 e 217 dias de idade. A utilização de somatotropina exógena possibilitou maior hipertrofia das fibras musculares brancas de contração rápida em bezerros suplementados em creep feeding durante a fase de cria, sem interferir na frequência de distribuição dos tipos de fibras no músculo Semitendinosus.

Electromyographic activity of the mandible muscles at the beginning and end of masticatory cycles in patients with complete dentures

The aim of this study was to assess the electrical activity of the masseter and anterior temporal muscles in subjects with severe bone resorption at two different times: ( a) the initial period, with the complete dentures they had worn for over 10 years, and (b) the final period, 5 months after having new dentures put into place. Twelve asymptomatic subjects were asked to respond to the questionnaire, according to the research diagnostic criteria for temporomandibular disorders, before denture rehabilitation and 5 months after the new dentures were put in place. The electrical activity of the muscles was recorded during mastication in the initial and final period, using artificial food (Optocal). The operator monitored the 35 chewing cycles that were repeated to grind the artificial food. After wearing the new dentures for 5 months, the right anterior temporal muscle showed a statistical difference before and after denture rehabilitation at the beginning and end of mastication. Muscular capacity and ability reduced the electrical activity in the masseter muscles after rehabilitation. Copyright (c) 2008 S. Karger AG, Basel.

Morphological and histochemical study of the myotomal muscle in pacu (Piaractus mesopotamicus Holmberg, 1887) during the initial growth phases

Morphological and histochemical methods were used to evaluate the myotomal muscle characteristics of pacu (Piaractus mesopotamicus) from hatching to 40 days old. During the larval period, the musculature consisted predominantly of white muscle. White and red muscle mass increased at 10, 20, 30 and 40 days after hatching. The larvae had round muscle fibers with a moderate degree of maturation and central nuclei. In subsequent phases, small and immature fibers were visible near larger and more differentiated fibers. Undifferentiated cells or presumptive myoblasts located in embryogenic zones were visible in the dorsal and ventral regions, and were more evident at 30 and 40 days. The red muscle fibers located in the subdermal region, had oxidative metabolism and slow contraction, whereas the more predominant white muscle fibers had glycolytic metabolism and fast contraction. Our findings indicate that during the initial phases, myotomal muscle growth in pacu occurs by both, muscle fiber hypertrophy and hyperplasia. The analysis of frequency of red and white muscle fibers shows that hyperplastic growth is intense in this period. As the growth rate in adult fish is related to the number of muscle fibers in young fish, extrinsic factors could change the muscle fiber phenotype and influence their ultimate size.