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Biomedical subjects

B S Shenkman

Publications and source records attributed to B S Shenkman.

At least 19 recordsLinked to original sources
PubMed2000

Histochemical responses of human soleus muscle fibers to long-term bedrest with or without countermeasures.

Effects of 2- or 4-month bedrest in -6 degrees head-down tilt position with or without countermeasures on the histochemical properties of fiber phenotype and cross-sectional area (CSA) were studied in human soleus. The CSAs in slow fibers decreased approximately 32% during 4-month bedrest. This reduction was normalized after 1-month recovery. Although the reduction of percent slow fibers was not significant statistically, the percent intermediate fibers was significantly elevated 4 months after bedrest. Such shift in fiber type was not normalized following 1-month recovery. Effects of wearing an anti-g Penguin suit which has a modest, but continuous resistance at the knee and ankle (Penguin-1) or with knee resistance without loading on the ankle (Penguin-2) for 10 consecutive hours daily were also investigated during approximately 2 months of bedrest. The subjects performed knee extension and flexion for the last 15 min of each hour while in a supine position in bed. Bedrest-induced fiber atrophy was prevented in the Penguin-1 group but not the Penguin-2 group. Transformation of fiber type was not prevented in either Penguin suit group. It is suggested that long-term bedrest causes an atrophy and a shift of fiber phenotype toward fast-twitch type in human soleus. Data also indicated that loading on the muscle is an effective countermeasure for prevention of fiber atrophy but not fiber-type transformation.

Adult↗
PubMed2000

[Concentration of macroergic phosphates and oxidative potential of skeletal muscles].

It is known that a long-duration decline of high-energy phosphate (HP) level in skeletal muscles, induced by administration of beta-guanidinpropionic acid (beta-GPA), is followed by an increase in mitochondrial enzyme activities (MEA). The same increase in MEA was observed in the course of physical exercise training. Under gravitational inloading decrease in MEA and increase in the level of high-energy phosphates occurred. If changes in (HP) level are believed to trigger the alterations in MEA, the increase in high-energy phosphate levels in muscles is to lead to a decline in MEA as well. The present work was purposed to reveal if changes in HP level under different contractile activity levels may be associated with changes in oxidative potential in the skeletal muscles.

Animals↗
PubMed2000

[Ultrastructure of skeletal muscle fibers in monkeys after space flight].

It is known that exposure of humans and animals to microgravity causes reduction in the cross-sected area of muscle fibers and muscle atrophy. These changes also involve ultrastructural alterations in muscle fibers. Therefore primates, that are physiologically close to humans, are to be examined to help a better understanding of the nature of these ultrastructural changes is muscles and muscle fibers. Although failed to find any relevant published data on the quantitative aspects of ultrastructural changes in muscle fibers of space-flown primates we believe that it is important to examine these aspects. The postflight study of monkey's m. soleus, and m. vastus lateralis did not reveal any significant changes in volume density of the myofibrillar apparatus. Mitochondria of m. soleus showed a distinct reduction in volume density, being more obvious in the subsarcolemmal zone than in the central one. Mitochondria of m. vastus lateralis showed a decrease (P > 0.05) in volume density. Following the flight, m. soleus and m. vastus lateralis of the monkeys showed a significant increase in the mean area of myofibrils, and a trend towards a decrease in the number of myofibrils per 100 micron 2. Besides, m. soleus showed a significant increase in the mean area of mitochondria, and a trend towards a decrease in the number of mitochondria per 100 micron 2. In m. vastus lateralis of the monkeys after space flight the number opf mitochondria tended to decrease and the mean area showed differential changes. It can be postulated that these phenomena may be associated with a reduction in the diffusion surface of mitochondria resulting from the diminished myofibrillar volume.

Animals↗
PubMed1999

Myonuclear domain and myosin phenotype in human soleus after bed rest with or without loading.

After 2 or 4 mo of bed rest (6 degrees head-down tilt) and 1 mo of ambulation, there was a tendency toward a higher percentage of fibers expressing fast myosin heavy chain (MHC) isoforms and a de novo appearance of fibers coexpressing type I+IIa+IIx and IIa+IIx MHC in human soleus fibers. After 2 and 4 mo of bed rest, the mean size of type I fibers decreased by 12 (P > 0.05) and 39%, respectively. Because myonuclear number/mm of fiber length was unchanged, myonuclear domain was smaller after bed rest than before. The mean size and myonuclear domain of type I fibers were largest after 1 mo of recovery. The effects of wearing an antigravity device (Penguin suit), which had a modest but continuous resistance at the knee and ankle (Penguin-1) or knee resistance without loading on the ankle (Penguin-2), for 10 consecutive h/day were determined during 2 mo of bed rest. Mean fiber sizes in Penguin-1, but not Penguin-2, group were maintained at or above pre-bed-rest levels, whereas neither group showed phenotype changes. Myonuclear domain in type I fibers was larger in Penguin-1 and smaller in Penguin-2 group post- compared with pre-bed rest, indicating that a single daily 10-h bout of modest muscle loading can prevent bed-rest-induced soleus fiber atrophy but has minimal effect on myosin phenotype. The specific adaptive cellular strategies involved may be a function of the duration and magnitude of the adaptive stimulus as well as the immediate activity history of the fiber before the newly changed functional demands.

Adult↗
PubMed1993

[The effect of spaced hypobaric hypoxia on the maximal hydraulic conductivity of the vascular bed, the supply of capillaries to and the size of the muscles fibers in rats].

6-7-month-old male Wistar rast were divided into three groups. On group of rats remained intact and lived under normal conditions (Group 1; n = 12). Groups 2 (n = 12) and 3 (n = 14) were exposed in hypobaric chamber (18-20 h a day and 2 h a day, respectively) for 2 weeks. The partial O2 pressure was maintained equivalent to 5000 m altitude. The hypoxia produced decreases of structural vascular resistance in hindquarters in Group 2 by 20-25% and in Group 3 by 17-20% (p < 0.05) under all perfusion pressure values. No significant changes in capillary density, capillary per fibre ratio in m. extensor hallucis proprius were found in rats exposed to hypobaric hypoxia for both durations. The cross-sectional area type I fibres (but not II fibres) (CSA) in Group 2 was significantly (p < 0.05) decreased (611 +/- 44 microns 2 vs 779 +/- 49 microns 2 in controls), continuous hypoxia produces significant reduction in type I fibre diffusion distances.

Animals↗
PubMed1993

[Effect of training on the structural-metabolic indicators in athletes' skeletal muscles].

Muscle biopsy samples were taken from m.vastus lateralis of ski-runners during the training season and 4 months after training (consisting presumably of aerobic exercises). Metabolic enzyme activities, fiber cross-sectional areas, capillary supply indices and parameters of oxygen uptake by intact mitochondria in skinned fibers were measured. Training did not induce any appreciable changes in the NADH-tetrazolium reductase activity, maximal oxygen uptake by mitochondria, mean fiber size or capillary density. At the same time, there were significant increases in the cytochrome c oxidase activity, respiratory control index and creatine-stimulated respiratory rate. The activities of alpha-glycerophosphate dehydrogenase, malate dehydrogenase and myoglobin peroxidase as well as the basal respiratory rate of mitochondria decreased as a result of training. The data obtained testify to the possibility of qualitative adaptations in the respiratory chain of mitochondria.

Adolescent↗
PubMedDate not supplied

[The morphological adaptation of the fibers of the human m. triceps surae during local endurance training].

Under investigation were effects of local endurance training of triceps of the calf in physically active volunteers who performed plantar bending in the talocrural articulation 3-4 times a week for 8 weeks with 30% of the maximum arbitrary effort for 40 minutes with 60 movements a minute. The exercise was fulfilled by one foot only. The local training resulted in a 19% greater density of capillaries in the triceps of the calf and in 30% greater amount of capillaries per a fiber. No significant changes were found during training in the ratio of the I and II types of fibers and in their area of cross section, although a tendency for hypertrophy of the Ist type fibers was noticed. Changes in the cross section area of the Ist type fibers and capillary density during training had a considerable negative interrelation. These findings show that the character of the muscle response to training is determined by a correlation of the parameters characterizing its initial state and the parameters of the morphological optimum, corresponding to the given level of functional activity.

Adaptation, Physiological↗