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S R Kayar

Publications and source records attributed to S R Kayar.

At least 37 records · Page 2Linked to original sources
PubMed1989

Total muscle mitochondrial volume in relation to aerobic capacity of horses and steers.

The relationship between maximal oxygen consumption rate (VO2max) and mitochondrial content of skeletal muscles was examined in horses and steers (n = 3 each). Samples of the heart left ventricle, diaphragm, m. vastus medialis, m. semitendinosus, m. cutaneous thoracicus and m. masseter, as well as samples of muscles collected in a whole-body sampling procedure, were analyzed by electron microscopy. VO2max per kilogram body mass was 2.7 x greater in horses than steers. This higher VO2max was in proportion to the higher total volume of mitochondria in horse versus steer muscle when analyzed from the whole-body samples and from the locomotor muscle samples. In non-locomotor muscles, total mitochondrial volume was greater in horses than steers, but not in proportion to their differences in VO2max. The VO2max of the mitochondria was estimated to be close to 4.5 ml O2.ml-1 mitochondria in both species. It is concluded that in a comparison of a highly aerobic to a less aerobic mammalian species of similar body size, a higher oxidative potential may be found in all muscles of the more aerobic species. This greater oxidative potential is achieved by a greater total volume of skeletal muscle mitochondria.

Animals↗
PubMed1989

Oxidative capacity of muscle and mitochondria: correlation of physiological, biochemical, and morphometric characteristics.

The oxidative capacity of cat skeletal muscles (soleus, gracilis, and gracilis chronically stimulated for 28 days) was derived from the total mitochondrial content in the muscle, the surface area of mitochondrial inner membranes, and respiratory activities of isolated mitochondria. Mitochondrial content was estimated by standard morphometry. The surface area of mitochondrial inner membranes per unit volume of mitochondria was estimated by a stereological method. The respiratory activities of isolated mitochondria were measured biochemically, using pyruvate/malate, glutamate/malate, succinate, or cytochrome c as substrate. Structurally and functionally, mitochondria from the three muscle types showed nearly identical characteristics. Oxidative activity was dependent on substrate; with succinate, 5.8 ml of O2 per min per ml of mitochondria was the rate most likely to represent physiological conditions. Oxidative activities of 3.1 ml.min-1.ml-1 with pyruvate/malate and 14.5 ml.min-1.ml-1 with cytochrome c as substrates were theoretical lower and upper bounds. The oxidative capacity of each of the three muscles was thus in direct proportion to the total volume of mitochondria in the muscle. The respiratory capacity of isolated mitochondria was very near to the maximal oxygen uptake rate of mitochondria that is commonly estimated in intact muscles of a wide variety of animals.

Animals↗
PubMed1989

Oxygen transport during exercise in large mammals. I. Adaptive variation in oxygen demand.

This study investigated mechanisms used by horses and steers to increase O2 uptake and delivery (VO2) from resting to maximal rates and identified the mechanisms that enable horses to achieve higher maximal rates of O2 consumption (VO2max) than steers. VO2 and circulatory variables were measured while Standardbred trotting horses and steers (450-kg body mass) stood quietly and ran on a treadmill at speeds up to those eliciting VO2max. As VO2 increased in both species, heart rate and circulating hemoglobin (Hb) concentration increased, thereby increasing O2 delivery by the circulation, while cardiac stroke volume remained unchanged. At VO2max arterial PCO2 increased from its resting value in horses but was unchanged in steers, and arterial PO2 decreased in both species. Although the horses hypoventilated and were hypoxemic at VO2max, no significant decrease in arterial Hb saturation occurred. VO2max of the horses was 2.6 times higher than that of the steers and was associated with a 100% larger cardiac output, 100% larger stroke volume, and 40% higher Hb concentration, whereas heart rates at VO2max were identical in the two species. The higher cardiac output of the horses at VO2max resulted from a 1.2-fold higher mean arterial pressure and 1.6-fold lower peripheral tissue resistance (associated with a larger skeletal muscle capillary bed). Both the magnitude of the difference in VO2max between horses and steers and the mechanisms used to achieve it are the same as observed in smaller pairs of mammalian species with large variation in aerobic capacity.

Adaptation, Physiological↗
PubMed1988

Mitochondrial size and shape in equine skeletal muscle: a three-dimensional reconstruction study.

Individual mitochondria were reconstructed from ultrathin serial sections of selected muscle fibers in the M. semitendinosus of a horse, over a length of nearly two sarcomeres. Mitochondria were found to be highly variable, with size and complexity of single mitochondria increasing with the fractional part of a fiber occupied by mitochondria. In fibers with a mitochondrial volume density of less than 4%, corresponding to the mitochondrial content of fast-twitch glycolytic fibers, mitochondria were generally rather simple cylindrical shapes, oriented parallel to the myofibrils. In fibers with a mitochondrial volume density of more than 7%, corresponding to the mitochondrial content of slow-oxidative or fast-oxidative glycolytic fibers, mitochondria were generally cylindrical at the A-band and Z-plate level of the muscle sarcomeres. However, these mitochondria often had transverse extensions or interconnections that occurred at the I-band level. Volumes of individual mitochondria ranged from as small as a few thousandths of a micron3 up to several micron3 for the incompletely reconstructed portions of the largest mitochondria. Mitochondrial profiles that one would classify from single sections as subsarcolemmal were found to interconnect with other profiles deeper within the fiber. This suggests that it is unlikely that subsarcolemmal and interfibrillar mitochondria are two structurally distinct populations. However, we found no evidence of a reticulum completely interlinking all mitochondrial material in a muscle fiber.

Animals↗
PubMed1988

Variability of fiber size, capillary density and capillary length related to horse muscle fixation procedures.

Muscle samples were taken from the superficial part of the semitendinosus muscle of four standardbred horses to compare the effects of three different fixation procedures on fiber size and capillarity. Infiltration fixation in an extended position of the muscle was compared to immersion fixation and infiltration fixation in a flexed position of the limb. The capillary length density was used to estimate muscle capillarity. Infiltration fixation was found to be a viable alternative to perfusion fixation of muscles for morphometry of fiber size and capillary length density allowing muscle tissue fixation at a defined sarcomere length without fiber kinking.

Animals↗
PubMed1988

The similarity of mitochondrial distribution in equine skeletal muscles of differing oxidative capacity.

A morphometric analysis was performed on horse muscle tissue to quantify mitochondrial distribution relative to capillaries. Samples of M. vastus medialis, M. semitendinosus, M. masseter and M. cutaneus thoracicus were preserved in a glutaraldehyde fixative for electron microscopy, or frozen for biochemical and histochemical analysis. These four muscles varied from highly oxidative in type, consisting nearly completely of type I fibres, in masseter, to highly glycolytic, primarily type IIb fibres, in cutaneus. In all four muscles, mitochondria were found in highest volume density near capillaries at the fibre border, with a sharp decline in volume density towards the fibre centre. This distribution was independent of myoglobin concentration, muscle fibre type and the activities of three key metabolic enzymes, citrate synthase, 3-OH-acyl-CoA dehydrogenase and lactate dehydrogenase.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1987

Volume density and distribution of mitochondria in myocardial growth and hypertrophy.

The volume density and distribution of mitochondria relative to capillaries have been measured using the technique of point counting in concentric rings, on normal and hypertrophied guinea pig myocardium. Right ventricular hypertrophy was produced by hypobaric hypoxia. In control guinea pigs right ventricular weight increased linearly with body weight. In control and hypoxic guinea pigs fiber cross sectional area (FCSA) and ventricular weight were related by a single straight line. Capillary density decreased hyperbolically with FCSA in both control and hypoxic animals. Capillary density was significantly higher (P less than 0.001) in the right ventricles of the hypoxic animals than in controls when the fibers were small but this difference disappeared as the fibers hypertrophied beyond FCSA values of 260 microns2. Volume density of mitochondria reached a peak (29-35%) close to the capillary but then decreased significantly in the spaces farthest from the capillary (mean 25.2%). There was no significant difference in peak mitochondrial volume density in controls versus hypoxic animals. There was thus an increase in the total volume of mitochondria in these myofibers that was in direct proportion to the increases in FCSA and heart volume. The highest volume density of mitochondria was found at a distance that is approximately 15% of the total distance over which O2 must diffuse in myocardial tissue and the peak volume density of mitochondria was thus a function of capillary density. The speculation is presented that the distribution of mitochondria may be related both to oxygen supply to the mitochondria and to the movement of high energy phosphate compounds out of mitochondria for use by myofibrils.

Animals↗
PubMed1986

Acute effects of endurance exercise on mitochondrial distribution and skeletal muscle morphology.

Biopsies of vastus lateralis from seven well-trained males were studied 1 month before and 15-30 min after a 100-km race. The distribution of interfibrillar mitochondria was analyzed to determine whether a long bout of exercise induced a redistribution of mitochondria. Capillary densities and mean fiber areas were also estimated. Capillary density and mean interfibrillar mitochondrial volume density were found to be significantly correlated with running time in the race. An earlier study on these biopsies found that the mean volume densities of interfibrillar and subsarcolemmal mitochondria did not change after a race, but the volume densities of lipid droplets and interfibrillar glycogen decreased significantly. In the present study, volume density of interfibrillar mitochondria [Vv(mi,fim)] before the race was highest with a value of 0.098 +/- 0.007 near the fiber border, and decreased progressively with distance to 0.045 +/- 0.004 at the fiber center. After the race, Vv(mi,fim) was unchanged at the fiber border, but was significantly higher (0.062 +/- 0.005) in the center of the fiber. This increase in mitochondrial volume density was attributable to the shrinkage of the fibers from consumption of energy stores, which was relatively greater for interfibrillar glycogen than for subsarcolemmal glycogen. Thus the primary effect of this extended bout of endurance exercise on vastus lateralis was the nearly complete depletion of the interfibrillar glycogen and lipids, but there was no evidence of an acute redistribution of mitochondria.

Adult↗
PubMed1986

Mitochondrial distribution in relation to changes in muscle metabolism in rat soleus.

Rats were subjected to exercise programs of either brief running once weekly or endurance running daily on a laddermill for 6 weeks. Both groups of exercised rats showed significant hypertrophy of the soleus. This muscle was analyzed morphometrically to determine if these running programs induced significant differences in the distribution of interfibrillar mitochondria. Interfibrillar mitochondrial volume density in the endurance-trained and control groups was highest near the fiber border and decreased with distance toward the fiber center, whereas in the weekly-run rats interfibrillar mitochondrial volume density was not correlated with distance within the fiber. Absolute interfibrillar mitochondrial volume (Vmi) was approximately 50% higher in endurance-trained rats than in controls at all locations sampled, but Vmi was nearly 80% higher in the weekly-run animals only in the fiber center. Thus the distribution of mitochondria was significantly different in weekly-run versus endurance-trained animals which may reflect differences in substrate source or high-energy phosphate flux in these fibers.

Animals↗
PubMed1986

Capillarity and mitochondrial distribution in rat myocardium following exercise training.

Rats were subjected to a laddermill running programme either once per week for 6 weeks, or daily for 6 weeks. Heart mass and maximal oxygen consumption rate increased relative to controls and with the frequency of the running programme. Mitochondrial distribution, measured in seven regions within fibres, was similar in all hearts, with a peak volume density of 0.42 +/- 0.01 occurring 4-5 microns from the centre of a capillary. Capillary density decreased with increasing heart mass, but total capillary length and capillary-to-fibre ratio were constant. Thus the higher metabolic demands of the running programmes did not alter the volume density or distribution of mitochondria, despite significant increases in heart mass and decreases in capillarity.

Adenosine Triphosphate↗
PubMed1985

Myocardial capillarity in acclimation to hypoxia.

Capillarity, O2 diffusion distances and fiber cross-sectional growth were measured in the hearts of guinea pigs exposed early during growth to hypobaric hypoxia (PB = 430 torr, PO2 = 90 torr). Twelve 5-week old males were maintained in a hypobaric chamber for 4-14 weeks. Their hearts were perfusion-fixed via the aorta with a 2.5% glutaraldehyde, 1% formaldehyde buffered solution; blocks were cut from left (LV) and right (RV) ventricles, post-fixed in OsO4, dehydrated and embedded in Spurr medium. Blocks were cut transversely to fiber orientation, 0.5 micron thick, stained with Toluidine Blue, and photographed at 400 X. Number and location of capillaries and fiber cross-sectional areas (FCSA) were scored from these photographs and from those of normoxic controls. Growth rates were similar for control and hypoxic guinea pigs. As animals grew, LV and RV weights increased linearly with body weight. Hypoxic guinea pigs had LV weights similar to controls but the RV showed varying degrees of hypertrophy. Control and hypoxic guinea pigs showed similar linear increases in FCSA with ventricular weight, suggesting that hypertrophy was due to increased FCSA. Capillary density (CD) decreased and capillary-to-fiber ratio (C:F) increased with FCSA, and O2 diffusion distances lengthened in LV and RV of animals in both groups. CD and C:F were higher and O2 diffusion distances were shorter in most hypoxic animals compared to controls. When RV hypertrophy was large (RV greater than 0.7 g) and failure imminent, CD, C:F and O2 diffusion distances were similar to controls suggesting that in these hearts oxygenation was impaired.

Acclimatization↗
PubMed1985

Sequential perfusion of skeletal muscle capillaries.

Rats were injected intraarterially with a fluorescent dye that binds to capillary endothelium, thereby labeling any capillary through which it has passed. After 10, 15, or 30 sec of circulation of the dye blood flow was interrupted, the gastrocnemius was frozen, and the density and distribution of labeled capillaries were measured in transverse sections of the central portion of the medial head. These tissue sections were then counterstained by the myosin ATPase method for capillaries to mark all capillaries. After 10 sec, 45% of all capillaries were labeled and after 15 sec, 59% of all capillaries were labeled. Thirty seconds after injection, all capillaries were labeled with the fluorescent dye. In all three time intervals, the distributions of labeled capillaries were ordered, suggesting that there is a tissue-level control mechanism for regulating capillary perfusion to maintain relatively short maximal oxygen diffusion distances.

Adenosine Triphosphatases↗
PubMed1985

Volume overload hypertrophy elicited by cold and its effects on myocardial capillarity.

Capillarity and fiber cross-sectional areas were measured in the hearts of guinea pigs exposed to cold early during growth. Twelve male guinea pigs were kept at 5 +/- 1 degrees C for 4-18 weeks. Hearts were perfusion fixed via the aorta with a 2.5% glutaraldehyde, 1% formaldehyde-buffered solution, blocks were cut from left (LV) and right (RV) ventricles, post-fixed in OsO4, dehydrated and embedded in Spurr medium. Blocks were cut transversely to fiber orientation, 0.5 micron thick, stained with Toluidine Blue and photographed at 400 x. Heart weights, number and location of capillaries and fiber cross-sectional areas (FCSA) were measured in cold-acclimated animals and in normothermic controls. Growth rates for all guinea pigs were similar. Acclimation to cold caused modest LV and RV hypertrophy. The greater LV weight seemed due to longer fibers of normal FCSA, whereas the greater RV weight was due to larger FCSA. Capillary density, capillary-to-fiber ratio and number of capillaries around the fibers were similar in the two groups of animals. Mean and maximal diffusion distances in cold-acclimated animals were not different from controls. Thus the myocardial hypertrophy induced by chronic volume overload was fully compensated for by increases in capillarity commensurate with increases in fiber girth.

Acclimatization↗
PubMed1985

Increased capillarity in skeletal muscle of growing guinea pigs acclimated to cold and hypoxia.

Capillarity was evaluated on transverse sections of frozen gastrocnemius and soleus muscles of young, growing guinea pigs exposed to the combined stresses of cold (6 degrees C) (C) and hypoxia (ambient PO2 = 85 Torr) (H) for up to 16 weeks and these data were compared to those obtained in a control group of guinea pigs kept in Denver (22 degrees C, ambient PO2 = 133 Torr). Capillarity was assessed from measurements of capillary density and capillarity density to fiber density ratios. Mean (R) and maximal (R95) diffusion distances were measured by the closest individual method. The body growth rate of guinea pigs exposed to C + H was the same as that in the control condition. The gastrocnemius muscle grew at the same rate as in the control guinea pigs. Exposure to C + H produced a significant (P less than 0.001) increase in the capillary density and the C/F of the gastrocnemius, reducing the mean and the maximal diffusion distances. However, the soleus muscles of the guinea pigs in C + H did not grow at the same rate and relative to body size the soleus muscles of these guinea pigs in C + H were smaller due to their smaller fiber cross-section area; consequently, there was a relatively larger capillarity in these muscles. It is hypothesized that the increased muscle capillarity in animals exposed to C + H results from a marked lowering of the tissue PO2 which may result from a leftward shift of the Hb-O2 dissociation curve.

Acclimatization↗
PubMed1984

Effects of hypoxia on tissue capillarity in geese.

Tissue capillarity in the gastrocnemius and myoglobin concentrations in the gastrocnemius and heart were determined for hatchling Canada geese, Branta canadensis, following incubation of the embryos under either normoxic (Po2 = 120 torr) or hypoxic (Po2 = 94 torr) conditions. Similar observations were made on a limited number of hatchling bar-headed geese, Anser indicus, a species native to high altitude. Capillary densities were higher and diffusion distances shorter in the hypoxic Canada geese and the bar-headed geese than in the normoxic Canada geese. The concentrations of myoglobin in the heart and gastrocnemius increased with mass, but not as a function of hypoxia. We conclude that bird embryos respond to hypoxia by increasing capillarity. The increased capillarity is found in species native to high altitude when incubated under conditions of normoxia and can be induced in species native to sea level by exposure to hypoxia during development.

Adaptation, Physiological↗
PubMed1983

Distribution of capillaries and diffusion distances in guinea pig myocardium.

A frequency distribution of distances from random points to the nearest capillary was generated from high-magnification photomicrographs of thin sections of the myocardium of seven guinea pigs. Individual mean capillary densities taken from regions viewed in transverse section ranged from approximately 1800 to 2500 capillaries/mm2. Mean (R) and maximal (R95) diffusion distances measured by the closest individual method ranged from R = 6.6 to 8.7 microns and R95 = 11 to 18 microns. Further mathematical analysis of the frequency distributions of diffusion distances indicated that the capillaries of the myocardium are distributed in an ordered array.

Animals↗