The effect of thyroid hormones on the aerobic development of locomotor and cardiac muscles in the barnacle goose

The role of thyroid hormones in the development of the locomotor and cardiac muscles of the barnacle goose (Branta leucopsis) was investigated. From 2 weeks of age, goslings were treated with thyroxine, triiodothyronine, or methimazole (a thyroid inhibitor). Birds were killed at 6 weeks (n = 5) or 9 weeks (n = 4) and various locomotor and cardiac muscle masses recorded and tissue samples taken for analysis of citrate synthase activity. The effects of thyroxine and triiodothyronine were not significantly different from each other, except in the case of the iliofibularis at 9 weeks. The mass-specific citrate synthase activity of the iliofibularis, semimembranosus muscles and liver were significantly increased by thyroid hormone treatment. Cardiac muscle showed a significant hypertrophy at 9 weeks of age following treatment with thyroxine. Hypothyroidism induced by treatment with methimazole exhibited the greatest effect on the pectoralis muscle, reducing citrate synthase activity by 33%. Mass-specific citrate synthase activity of the pectoralis and pectoralis mass (% body wt.) were found to be highly correlated (r ² = 0.74) at 6 weeks of age. It is suggested that thyroid hormones may be involved in controlling the tissue-specific timing of the maturation of locomotor and cardiac muscles. Accepted: 16 September 1996     

Energy metabolism of fast- and slow-twitch skeletal muscle in the rat: Thyroid hormone induced changes

Summary Male Wistar rats were made hypothyroid or hyperthyroid over a period of six weeks, by administration of carbimazole or triiodothyronine (T₃). Serial frozen sections of soleus and extensor digitorum longus (EDL) muscle were stained histochemically for myosin ATPase, succinic dehydrogenase and phosphorylase. Muscle fibres were classified as either slow twitch oxidative (SO), fast twitch oxidative glycolytic (FOG) or fast twitch glycolytic (FG). In addition the activities of phosphorylase, phosphofructokinase (PFK), fructose-1,6-diphosphatase (FDP), lactate dehydrogenase (LDH), hexokinase, citrate synthetase, cytochrome oxidase, 3-hydroxyacyl-CoA dehydrogenase (HAD) and 5-AMP aminohydrolase were measured in both muscles.Increasing plasma levels of T₃ are associated with marked alterations in the fibre type populations in both muscles. In the soleus there is conversion of SO to FOG fibres while in the EDL, FG fibres are converted to FOG fibres. The quantitative changes in metabolic enzyme activity however, are in the main restricted to the soleus. Increased T₃ levels result in an increased capacity for the aerobic metabolism of both fat and carbohydrate and an increase in anaerobic glycolytic activity in the soleus muscle which parallels the change in fibre types. However, the extent of these increases cannot be explained solely on this basis and there is also an overall increase in aerobic activity in all fibres including slow oxidative ones. It is concluded that the effects of thyroid hormone on muscle phenotype and respiratory capacity involve both primary and secondary sites of action and the possible mechanisms are discussed.Abbreviations EDL extensor digitorum longus - FDP fructose-1,6-diphosphatase - FG fast twitch glycolytic - FOG fast twitch oxidative glycolytic - HAD 3-hydroxyacyl-CoA-dehydrogenase - LDH lactate dehydrogenase - PFK phosphofructokinase - SO slow twitch oxidative - T ₃ triiodothyronine - T ₄ thyroxine     

Histochemical and biochemical properties of flight muscle fibers in the little brown bat,Myotis lucifugus

Summary The purpose of this investigation was (1) to determine the fiber composition of pectoralis muscle of the little brown bat,Myotis lucifugus; (2) to compare the fiber composition of this muscle with two of the animal's accessory flight muscles; and (3) to study the effect of hibernation on pectoralis muscle fiber composition. Bat skeletal muscle fibers were also compared with those of white laboratory rats (Rattus norvegicus). Bat pectoralis muscles possessed exceptionally high oxidative capacities as indicated by their succinate dehydrogenase activities, but relatively low glycolytic potentials (phosphofructokinase activities). Muscle histochemistry demonstrated that fiber composition of bat pectorlis muscle was homogeneous; all fibers possessed high aerobic and low glycolytic potentials, and high myofibrillar ATPase activities indicating fast contractile properties. In contrast, accessory flight muscles possessed three distinguishable fiber types. During hibernation there was a significant decline in oxidative potential, no change in glycolytic potential, and no alteration in basic fiber composition of bat pectoralis muscle. The findings of this study suggest that pectoralis muscles ofM. lucifugus may approach the ultimate adaptation of a mammalian locomotory muscle for aerobic generation of muscular power.Abbreviations FG fast-twich glycolytic - FOG fast-twitch-oxydative-glycolytic - -GPDH -glycerophosphate dehydrogenase - LDH lactate dehydrogenase - NADH-D reduced nicotinamide adenine dinucleotide diaphorase - PFK phosphofructokinase - SDH succinate dehydrogenase - SO slowtwich-oxidative     

A histochemical comparison of fibre types in the M. pectoralis and M. supracoracoideus of the great skua Catharacta skua and the herring gull Larus argentatus with reference to kleptoparasitic capabilities

Skuas, which are closely related to gulls, frequently use a specialized feeding method (kleptoparasitism) by which they rob other seabirds of their food. This paper tests the idea that skuas have evolved as specialist kleptoparasites.
The fibre type composition of the M. pectoralis, M. supracoracoideus and M. iliofibularis of a great skua Catharacta skua (Brünn.) and a herring gull Larus argentatus (Pontopp.) was determined by three enzyme histochemical methods commonly used for mammalian fibre classification; the reactions for alphaGPDH, NADH-TR and mATPase activity.
In both species slow fibres were present only in the M. iliofibularis, and fast twitch glycolytic fibres were not present in any of the muscles. The M. pectoralis and M. supracoracoideus of both species consisted entirely of the fast twitch oxidative-glycolytic fibres.
The overall metabolic enzyme activities of the muscles were assessed in terms of the proportions of fibres with high, intermediate and low metabolic enzyme activity. The overall levels of oxidative and glycolytic enzyme activity were significantly higher in the M. pectoralis than in the M. supracoracoideus and significantly higher in both of these than in the M. iliofibularis. This was true of both species.
The oxidative and glycolytic activities of all three muscles of the great skua were significantly higher than those of the homologous muscles of the herring gull. This was particularly true of the M. pectoralis and M. supracoracoideus. It is suggested that this difference between great skuas and herring gulls enables the former to be more effective aerial kleptoparasites than the latter.     

High altitude tissue adaptation in Andean coots: capillarity,fibre area,fibre type and enzymatic activities of skeletal muscle

Capillarity, fibre types, fibre area and enzyme activities of different skeletal muscles (pectoralis, extensor digitorum longus), tibialis anterior, plantaris and the myocardium were compared in Andean coot (Fulica americana peruviana) native to high altitude (Junín, Perú, 4200 m) and the same species nesting at sea level. Numbers of capillaries per square millimeter were higher in all high-altitude muscles when compared with sea-level muscles (P<0.0001). Moreover, values for capillaries per fibre and capillaries in contact with each fibre were higher in digitorum and tibialis high-altitude muscles. Muscle fibres were classified as Type I, Type IIA or Type IIB on the basis of their myofibrillar ATPase pH lability. Pectoralis muscle of high-altitude and sea-level coots presented only fibres of Type IIA. In contrast, all the leg muscles studied showed a mosaic pattern of the three fibre types. Fibre areas were determined using a Leitz Texture Analysis System. Significant differences in fibre area were observed (P<0.01) between high-altitude and sea-level muscles. Mean muscle fibre diameters were also lower in the high-altitude group than in the sea-level group. The enzyme activities studied were hexokinase, lactate dehydrogenase, citrate synthase and 3-hydroxyacyl-CoA-dehydrogenase. The oxidative capacity, as reflected by citrate synthetase and hydroxyacyl-CoA-dehydrogenase activities, was greater for myocardial and pectoralis than for leg muscles. However, analysis of maximal enzyme activities showed that there were no significant differences between the glycolytic and oxidative enzyme activities of high-altitude and sea-level coots. These results suggest that in Andean coots genetically adapted to high altitude, changes in muscle capillarity and fibre size, in addition to high haemoglobin O₂ affinity and low haemoglobin concentration, are sufficient to allow adequate energy production without increases in enzymatic activities.Abbreviations BSA bovine serum albumin - C:F ratio Capillaries per fibre - CAF Capillaries in contact with each fibre - CD capillary density (mm^-2) - CS citrate synthetase - EDL muscularis digitorum longus - fra fraction reduction area - HA high altitude - HAD hydroxyacyl-CoA-dehydrogenase - HK hexokinase - LDH lactate dehydrogenase - P ₅₀ PO₂ at which hemoglobin is half saturated with O₂ - P _aO₂ arterial partial pressure of oxygen - PAS periodic acid-schiff - PEC muscularis pectoralis - PLA muscularis planaris - P _tO₂ mean tissue oxygen pressure - P _vO₂ mixed venous partial pressure of oxygen - SD standard deviation - SL sea level - TA muscularis tibialis anterior - TAS texture analysis system     

Histochemical and biochemical plasticity of muscle fibers in the little brown bat (Myotis lucifugus)

Summary Fiber composition, and glycolytic and oxidative capacities of the pectoralis, gastrocnemius, and cardiac muscles from active and hibernating little brown bats (Myotis lucifugus) was studied. The data were used to test two hypotheses: First, since hibernating bats maintain the capability of flight and make use of leg muscles to maintain a roosting position all winter, the fiber composition of the pectoralis and gastrocnemius muscles should not change with season. Second, we tested the hypothesis of Ianuzzo et al. (in press), who propose that the oxidative potential of mammalian cardiac muscle should increase with increasing heart rate while glycolytic potential should not. Our results indicate that the fiber composition of the pectoralis muscle was uniformly fast-twitch oxidative (FO)_ regardless of the time of year, as predicted. However, the gastrocnemius muscle exhibited a change in FO composition from 83% in active to 61% in hibernating animals. Contrary to the variable change in histochemical properties with metabolic state, a trend of reduced maximal oxidative (CS) and glycolytic (PFK) potential during hibernation in both flight and leg muscles was apparent. The oxidative potential of flight and leg muscles decreased by 15.2% and 56.5%, respectively, while the glycolytic potential of the same muscles decreased by 23.5% and 60.5%, respectively. As predicted, the glycolytic potential of cardiac muscle remained constant between active and hibernating bats, although there was a significant decrease (22.0%) in oxidative potential during hibernation.Abbreviations FO fast-twitch oxidative - FG fast-twitch glycolytic - SO slow-twitch oxidative - Vmax maximal enzyme activity - PFK phosphofructokinase - CS citrate synthase     

Fibre types in primary ‘flight’ muscles of the African Penguin (Spheniscus demersus)

The African penguin (Spheniscus demersus) is an endangered seabird that resides on the temperate southern coast of Africa. Like all penguins it is flightless, instead using its specialized wings for underwater locomotion termed ‘aquatic flight’. While musculature and locomotion of the large Antarctic penguins have been well studied, smaller penguins show different biochemical and behavioural adaptations to their habitats. We used histochemical and immunohistochemical methods to characterize fibre type composition of the African penguin primary flight muscles, the pectoralis and supracoracoideus. We hypothesized the pectoralis would contain predominantly fast oxidative–glycolytic (FOG) fibres, with mainly aerobic subtypes. As the supracoracoideus and pectoralis both power thrust, we further hypothesized these muscles would have a similar fibre type complement. Our results supported these hypotheses, also showing an unexpected slow fibre population in the deep parts of pectoralis and supracoracoideus. The latissimus dorsi was also examined as it may contribute to thrust generation during aquatic flight, and in other avian species typically contains definitive fibre types. Unique among birds studied to date, the African penguin anterior latissimus dorsi was found to consist mainly of fast fibres. This study shows the African penguin has specialized flight musculature distinct from other birds, including large Antarctic penguins.     

Structure and Some Contractile Properties of Musculus Iliofibularis of Agama stellio stellio

Abstract The running speed of Agama stellio stellio was 2.1 ± 0.3 m s^?1 at preferred body temperature (T_b, 30°C). To account for sprint locomotion, we meaured two mechanical parameters and examined the ultrastructural features of a major locomotory muscle in normal walking and running locomotion, the iliofibularis muscle, which is considered to act as an extensor of the lower hind limb. The time to peak isometric twitch tension and time to half relaxation were 52 ± 7 ms and 76 ± 5 ms, respectively. The comparative ultrastructure of the fast and slow fibes provides structure-to-function correlation. The sarcoplasmic reticulum and T-tubules system are abundant in fast fibres which serve to transmit Ca²⁺ and spread the excitatory impulse intracellularly with great rapidity. In contrast, the membranous system of slow fibres is relatively poor and this indicates slow impulse propagation. Thus, these results show that the fast locomotion of Agama stellio stellio can, in part, be explained by the physiology and ultrastructure of the fibres of the locomotory muscles.     

Catabolic enzyme activities in relation to premigratory fattening and muscle hypertrophy in the gray catbird (Dumetella carolinensis)

Summary The flight muscles of the gray catbird (Dumetella carolinensis) were examined to determine if short term adjustments occur in the activity of key catabolic enzymes during preparation for long distance migration. The aerobic capacity of the pectoralis muscle as indicated by citrate synthase activity (CS) is among the highest reported for skeletal muscle (200 moles [min·g fresh mass]^–1 at 25°C). The mass specific aerobic capacity as indicated by CS activity or cytochromec concentration does not change during premigratory fattening (Fig. 2) or in relation to the muscle hypertrophy that occurs concomitantly. The maintenance of mass specific aerobic capacity indicates that the total aerobic capacity increases in proportion to the increase in muscle size. The augmented potential for total aerobic power output is considered an adaptation to meet the increased power requirements of flight due to the increased body mass. Additionally, the capacity to oxidize fatty acids, as indicated by -hydroxyacyl-CoA dehydrogenase activity, approximately doubles during premigratory fattening (from 35 to 70 moles [min·g fresh mass]^–1 at 25°C; Fig. 1A). This adaptation should favor fatty acid oxidation, thereby sparing carbohydrate and prolonging endurance. The activity of phosphofructokinase, a key glycolytic enzyme, does not change before migration.Abbreviations CPT carnitine palmitoyl transferase - CS citrate synthase - HOAD -hydroxyacyl-CoA-dehydrogenase - PFK phosphofructokinase     

Capillarity and fibre types in locomotory muscles of wild mallard ducks (Anas platyrhynchos)

Six locomotory muscles from wild mallard ducks (Anas platyrhynchos) were analysed by histochemical methods. Special care was taken in sample procedure in order to describe the heterogeneity found throughout each muscle. Capillarity and fibre-type distributions were correlated to the functional implications and physiological needs of each muscle. Comparisons between our results and similar previous reports on dabbling and diving ducks are also discussed. Muscles from the leg presented the most heterogeneous fibre-type distributions, which are correlated to the wide range of terrestrial and aquatic locomotory performances shown by these animals. More specialized muscles such as pectoralis, used almost exclusively for flapping flight, had more homogeneous fibretype distributions, whereas muscles from the wing presented a high proportion of glycolytic fibres probably recruited during non-steady flapping flight. Deep muscle pectoralis zones and parts of the gastrocnemius which are closer to the bone are remarkable for their high capillarity indices and oxidative capacities, which suggests that these parts are recruited during sustained flapping flight and swimming. However, two different strategies for achieving these high oxygen needs are evident, indicating that the fibre cross-sectional area plays an important role in the modulation of the oxygen supply to the muscle cells.Abbreviations AChE acetylcholinesterase - cap mm^-2 number of capillaries per square millimeter - CD capillary density - C/F capillary-to-fibre ratio - EMR muscle extensor metacarpialis radialis - FCSA fibre cross-sectional area - FD fibre density - FG fast glycolytic - FOG fast oxidative glycolytic - GLE muscle gastrocnemius lateralis (pars externa) - GPDH -glycerophosphate dehydrogenase - ITC muscle iliotibialis cranialis - m-ATPase myofibrillar adenosine triphosphatase - OFA oxidative fibre area - OFN oxidative fibre number - PEC muscle pectoralis - SCH muscle scapulohumeralis caudalis - SDH succinate dehydrogenase - SO slow oxidative - TSC muscle scapulotriceps or triceps scapularis     

Differential effects of thyroid status on regional H2O2 production in slow- and fast-twitch muscle of ducklings

Birds seem to employ powerful physiological strategies to curb the harmful effects of reactive oxygen species (ROS) because they generally live longer than predicted by the free radical theory of aging. However, little is known about the physiological mechanisms that confer protection to birds against excessive ROS generation. Hence, we investigated the ability of birds to control mitochondrial ROS generation during physiologically stressful periods. In our study, we analyzed the relationship between the thyroid status and the function of intermyofibrillar and subsarcolemmal mitochondria located in glycolytic and oxidative muscles of ducklings. We found that the intermyofibrillar mitochondria of both glycolytic and oxidative muscles down regulate ROS production when plasma T₃ levels rise. The intermyofibrillar mitochondria of the gastrocnemius muscle (an oxidative muscle) produced less ROS and were more sensitive than the pectoralis muscle (a glycolytic muscle) to changes in plasma T₃. Such differences in the ROS production by glycolytic and oxidative muscles were associated with differences in the membrane proton permeability and in the rate of free radical leakage within the respiratory chain. This is the first evidence which shows that in birds, the amount of ROS that the mitochondria release is dependent on: (1) their location within the muscle; (2) the type of muscle (glycolytic or oxidative) and (3) on the thyroid status. Reducing muscle mitochondrial ROS generation might be an important mechanism in birds to limit oxidative damage during periods of physiological stress.     

Ontogeny of catabolic and morphological properties of skeletal muscle of the red-winged blackbird (Agelaius phoeniceus)

Thermogenic capabilities of red-winged blackbirds improve markedly during their 10-12-day nestling period, especially between day 5 and day 8. The time course of improvements may be determined by the maturation of skeletal muscles involved in shivering thermogenesis, particularly the pectoralis muscles. To test this hypothesis, morphological and biochemical changes in pectoral and leg muscles were measured in young and adult blackbirds. Both muscles grew disproportionately relative to body mass. The pectoralis consisted entirely of fast-twitch fibers, predominantly fast oxidative glycolytic. In contrast, the gastrocnemius muscle consisted of a mixture of slow and fast fibers (predominantly fast glycolytic). Although fiber composition was constant, both cross-sectional area and density of fibers increased with age in both muscles. Catabolic capacities of the pectoralis increased significantly (approximately 7-8-fold) throughout the nestling period, most abruptly after day 3 (citrate synthase, CS) or day 4 (3-hydroxacyl-CoA-dehydrogenase, HOAD). Myofibrillar ATPase activities in the pectoralis were initially low, but increased after day 5. Further increases in CS and myofibrillar ATPase activities occurred in the pectoralis after fledging. CS and HOAD activities in the leg were much lower, but myofibrillar ATPase activities were remarkably similar in the two muscles, differing only in adults. These results are consistent with the hypothesis that the development of endothermy is dependent on the morphological and biochemical maturation of skeletal muscles important in thermogenesis.     

The role of muscle development in the transition to endothermy in nestling bank swallows,Riparia riparia

Summary We examined the transition from ectothermy to endothermy in nestling bank swallows (Riparia riparia) by measuring the peak metabolic response to cold (PMR) in groups of nestlings. Additionally aerobic capacity, as assessed by citrate synthase activity (CS), and contractile function, as assessed by myofibrillar ATPase activity (mATPase) were measured in the pectoralis and mixed leg muscles during development. During the first 65% of their growth (from 2–12 g) bank swallows do not increase their metabolic rate in response to cold (Fig. 1). Between 12 and 16 g the PMR increased from 4 to more than 10 ml O₂ (g·h)^–1. Citrate synthase activity increased throughout development, starting at 20 moles (min·g fresh mass)^–1 in both tissues and increasing to 150 and 50 moles (min·g)^–1 in the pectoralis and leg muscles, respectively (Fig. 5). The augmented aerobic capacity combined with large increases in muscle mass undoubtedly contributes to the improved thermoregulatory abilities of older nestlings. However, muscle mass and aerobic capacity increase continuously and do not show the sharp transition noted in PMR. In the leg muscle mATPase activity is constant throughout growth, but in the pectoralis muscle it undergoes an abrupt increase from 0.5 moles (min·mg myofibrillar protein)^–1 in animals weighing less than 12 g to 0.9 moles (min·mg)^–1 in nestlings weighing more than 15 g (Fig. 6). The similar pattern of development of PMR and mATPase suggests a critical role for muscle development in the transition to endothermy in this species.Abbreviations CS citrate, synthase - mATPase myofibrillar adenosine triphosphatase - PMR peak metabolic rate during cold stress - rate of oxygen consumption     

Comparative aspects of fibre types,areas, and capillary supply in the pectoralis muscle of some passerine birds with differing migratory behaviour

Summary Fibre types, fibre areas and capillary supply in the pectoralis muscle of fifteen passerines with four different patterns of migratory behaviour have been studied. The predominant fibre type was a fast-twitch oxidative-glycolytic which was the only fibre type present in all species, except in the robin and the blackbird where a fast fibre with intermediate oxidative capacity and a fast glycolytic fibre were also found. There was a significant difference in fibre areas between birds with different migratory strategies, with the long-distance migratory group having the smallest fibres. This also led to higher capillary densities, shorter diffusion distances and, consequently, more capillaries around the fibres relative to fibre area in this group. This indicates an adaptation in the morphology of the pectoralis muscle to differences in migration strategies. In the robin, the proportion of the intermediate fibre was significantly greater during the breeding season than during migration. Seasonal differences in fibre areas and capillary supply within a species were also seen, but no definite trends were detectable.Abbreviations CC capillary/fibre contacts - CCA mean number of capillaries in contact with a fibre relative to fibre cross-sectional area - MD mean diffusion length - CD capillary density - FG fast-twich glycolytic - FOG fast-twitch oxidative-glycolytic     

Phenotypic flexibility in passerine birds: Seasonal variation of aerobic enzyme activities in skeletal muscle

Improved winter cold tolerance is widespread among small passerines resident in cold climates and is generally associated with elevated summit metabolic rate (M_sum=maximum thermoregulatory metabolic rate) and improved shivering endurance with increased reliance on lipids as fuel. Elevated M_sum and improved cold tolerance may result from greater metabolic intensity, due to mass-specific increase in oxidative enzyme capacity, or increase in the masses of thermogenic tissues. To examine the mechanisms underlying winter increases in M_sum, we investigated seasonal changes in mass-specific and total activities of the key aerobic enzymes citrate synthase (CS) and β-hydroxyacyl CoA-dehydrogenase (HOAD) in pectoralis, supracoracoideus and mixed leg muscles of three resident passerine species, black-capped chickadee (Poecile atricapillus), house sparrow (Passer domesticus), and white-breasted nuthatch (Sitta carolinensis). Activities of CS were generally higher in winter than in summer muscles for chickadees and house sparrows, but not nuthatches. Mass-specific HOAD activity was significantly elevated in winter relative to summer in all muscles for chickadees, but did not vary significantly with season for sparrows or nuthatches, except for sparrow leg muscle. These results suggest that modulation of substrate flux and cellular aerobic capacity in muscle contribute to seasonal metabolic flexibility in some species and tissues, but such changes play varying roles among small passerines resident in cold climates.     

Sexual dimorphism in histological characteristics and contractility of the iliofibularis muscle in the lizard Sceloporus torquatus

The iliofibularis is a hindlimb muscle used in lizard locomotion that is composed of at least three types of fibres: fast‐twitch‐glycolytic (FG), fast‐twitch‐oxidative‐glycolytic fibre (FOG) and slow‐twitch‐oxidative (SO). The striated skeletal muscle is a highly plastic tissue undergoing phenotypic change in response to activity. The lizard Sceloporus torquatus has sexual differences associated with microhabitat use, which can be reflected in the physiology and anatomy of the muscle, and thus, in our study, we analysed the morphological and contractile characteristics of the iliofibularis muscle (IF) of S. torquatus males and females. We found a larger prevalence of FOG compared with FG and SO fibres in the muscle of both sexes. We also found that males show larger areas of the three types of fibres, develop greater strength but also faster fatigue than females, suggesting that strength is a key functional feature that enables males to perform faster movements (but for shorter periods), associated with the demands of territoriality.     

Capillarity and fiber types in locomotory muscles of wild common coots,Fulica atra

Six locomotory muscles of wild common coots, Fulica atra, were analyzed histochemically. Capillarity and fiber-type distributions were correlated to the functional implications and physiological needs of each muscle. Leg muscles exhibit three unevenly distributed fiber types, a pattern that reflects the great variety of terrestrial and aquatic locomotory performances that coots are able to develop. Aerobic zones are presumably recruited during steady swimming and diving, while regions with anaerobic characteristics may be used for bursts of activity such as sprint swimming or during take off, when coots run along the water's surface. Fiber types and capillarization in wing muscles have a marked oxidative trend. High wing beat frequencies, short and broad wings, and the long distance migrations that these birds perform indicate that the presence of high numbers of oxidative fibers and the well developed capillary supply are needed for enhanced oxygen uptake. The pectoralis muscle, except in its deep part, has exclusively fast oxidative fibers with a very high staining intensity for succinate dehydrogenase assay as compared to the same fiber type of other muscles. Its predominant role in flapping flight justifies these characteristics that are typical of fibers with high aerobic metabolism. The deep part of the pectoralis muscle presents a low proportion of an unusual slow anaerobic fiber type. These fibers could play a role during feeding dives when the bird presses the air out of the feathers by tightening the wings against the body. A linear relationship between capillary and fiber densities in all coot muscles studied reflects an adjustment between fiber diameter and vascularization in order to obtain the oxygen for mitochondrial supply. This strategy seems a suitable way to cope with the rigid aerobic constraints that flying and diving impose upon the coot's physiology. J. Morphol. 237:147–164, 1998. © 1998 Wiley-Liss, Inc.     

Fibre types in the locomotory muscles of an antarctic teleost,Notothenia rossii

Summary The metabolic and structural differentiation of locomotory muscles of Notothenia rossii has been investigated. In this species sustained locomotion is achieved by sculling with enlarged pectoral fins (labriform locomotion), whilst the segmental myotomal muscle is reserved for burst activity. Red, white and subepidermal fibres can be distinguished in the trunk by histochemical and ultrastructural criteria. The main pectoral muscle (m. adductor profundus) consists entirely of red fibres. These three main fibres types show differences in histochemical staining profiles, capillarization, myofibril shape and packing, and lipid and mitochondrial content. The fractional volume of mitochondria amounts to 38% for pectoral, 30% for red myotomal and 1.9% for white myotomal fibres. Enzyme activities of red pectoral muscle are consistent with a higher potential for aerobic glucose and fatty acid oxidation than for the red myotomal fibres. Mg²⁺ Ca²⁺ -myofibrillar ATPase activities are similar for red pectoral and myotomal muscles and approximately half of those white fibres. Specialisations of N. rossii muscles associated with labriform swimming and locomotion at Antarctic temperatures are discussed.     

Development of the aerobic dive limit and muscular efficiency in northern fur seals (Callorhinus ursinus)

Northern fur seal (Callorhinus ursinus; NFS) populations have been declining, perhaps due to limited foraging ability of pups. Because a marine mammal’s proficiency at exploiting underwater prey resources is based on the ability to store large amounts of oxygen (O₂) and to utilize these reserves efficiently, this study was designed to determine if NFS pups had lower blood, muscle, and total body O₂ stores than adults. Pups (<1-month old) had a calculated aerobic dive limit only ~40% of adult females due to lower blood and, to a much greater extent, muscle O₂ stores. Development of the Pectoralis (Pec) and Longissimus dorsi (LD) skeletal muscles was further examined by determining their myosin heavy chain (MHC) composition and enzyme activities. In all animals, the slow MHC I and fast-twitch IIA proteins typical of oxidative fiber types were dominant, but adult muscles contained more (Pec ~50%; LD ~250% higher) fast-twitch MHC IID/X protein characteristic of glycolytic muscle fibers, than pup muscles. This suggests that adults have greater ability to generate muscle power rapidly and/or under anaerobic conditions. Pup muscles also had lower aerobic and anaerobic ATP production potential, as indicated by lower metabolically scaled citrate synthase, β-hydroxyacyl CoA dehydrogenase, and lactate dehydrogenase activities (all P values ≤0.001). In combination, these findings indicate that pups are biochemically and physiologically limited in their diving capabilities relative to adults. This may contribute to lower NFS first year survival.     

The effect of corticosterone on standard metabolic rates of small passerine birds

Summary Resting metabolic rates of Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) and pine siskins (Carduelis pinus) were evaluated at thermoneutral temperatures before and after administration of corticosterone (B) at physiological doses. There was no effect of B on basal metabolic rate of either species, but nocturnal metabolic rate varied significantly less over the 3-h period of measurement in B-treated sparrows and siskins than in control birds. These results, coupled with observations of caged birds, suggest that corticosterone has no direct effect on avian resting metabolism but does reduce the responsiveness of birds to external stimuli and thus promotes nocturnal restfulness.Abbreviations B corticosterone - VO ₂ rate of oxygen consumption - T ₃ tri-iodothyromine - T ₄ tetra-iodothyronine, thyroxine