Biomedical subjects

T P Martin

Publications and source records attributed to T P Martin.

At least 19 recordsLinked to original sources

PubMed1992

The effects of a reduced exercise duration taper programme on performance and muscle enzymes of endurance cyclists.

The influence of tapering on the metabolic and performance parameters in endurance cyclists was investigated. Cyclists (n = 25) trained 5 days.week-1, 60 min.day-1, at 75-85% maximal oxygen consumption (VO2max) for 8 weeks and were then randomly assigned to a taper group: 4D (4 days; n = 7), 8D (8 days; n = 6), CON (control, 4 days rest; n = 6), NOTAPER (non-taper, continued training; n = 6). Muscle biopsy specimens taken before and after training and tapering were analysed for carnitine palmityltransferase (CPT), citrate synthase, beta-hydroxyacyl CoA dehydrogenase (HOAD), cytochrome oxidase (CYTOX), lactate dehydrogenase, glycogen and protein. Significant increases in VO2max (6%), a 60-min endurance cycle test (34.5%), oxidative enzymes (77-178%), glycogen (35%) and protein (34%) occurred following training. After the taper, HOAD and CPT decreased 25% (P less than 0.05) and 26% respectively, in the CON. Post-taper CYTOX values were different (P less than 0.05) for 4D and 8D compared with CON. Muscle glycogen levels were increased (P less than 0.05) after tapering in the 4D, 8D and CON, but decreased in NOTAPER. Similarly, power output at ventilation threshold was significantly increased in the 4D (27.4 W) and 8D (27 W) groups, but decreased (22 W) in the NOTAPER. These findings suggest that tapering elicited a physiological adaptation by altering oxidative enzymes and muscle glycogen levels. Such an adaptation may influence endurance cycling during a laboratory performance test.

Adult↗

PubMed1992

Intrafibre distribution of succinate dehydrogenase in cat tibialis anterior motor units.

Using isolated ventral root filament stimulation and glycogen depletion techniques, 14 motor units from the cat tibialis anterior were studied. Based on their mechanical properties, the units were classified as either slow-fatigue resistant, fast-fatigue resistant, fast-fatigue intermediate, or fast-fatigable. Quantitative histochemical and computer assisted image analysis techniques were used to determine the activity of succinate dehydrogenase in a population of fibres in each unit. In addition, the intrafibre distribution of succinate dehydrogenase activity was measured in those same fibres by calculating the enzymatic activity of circumferential layers every 0.5 microns starting from the fibre edge to its centre. It was established that enzymatic activity and radial distance were linearly related in the fibres. A range in succinate dehydrogenase activity (mean coefficient of variation, 29%) was observed among the fibres of a unit. In contrast, the intrafibre distribution of that activity was rather consistent (mean variation, 4%) across the fibres of a unit. Further, the intrafibre distribution was similar among the fibres of units classified as the same type. However, the intrafibre distribution was disparate among the different unit types. These data suggest that the intrafibre distribution of mitochondrial enzymes may contribute to the mechanical properties of a motor unit. In this regard, a hypothesis is proposed that describes how the absolute activity of a mitochondrial enzyme, and the intrafibre distribution of that activity, may interactively contribute to the fatigue resistance of a unit.

Animals↗

PubMed1992

Recovery of rat tibialis anterior motor unit properties following partial denervation.

The recovery of selected mechanical, morphological, and metabolic properties of rat tibialis anterior fast motor units was determined following partial denervation (n = 7) or partial denervation and hemispinal cord transection (n = 5) and compared with age-matched control units (n = 7). Following 1-12 months of recovery, the mechanical properties of each unit were measured and the fibres depleted of glycogen by using standard ventral root filament stimulation techniques. Quantitative histochemical techniques were used to determine cross-sectional area and the activities of succinate dehydrogenase and alpha-glycerolphosphate dehydrogenase in individual unit fibres. Partial denervation increased the mean fibre area but decreased alpha-glycerolphosphate dehydrogenase activity. Succinate dehydrogenase was unchanged in the denervated groups. The variability in area and enzymatic activities among the unit fibres was unchanged. However, the interrelationship between the enzymes was altered by both denervation procedures. Succinate dehydrogenase activity was directly related to fatigue resistance and inversely related to tetanic tension across the units. These findings suggest that a motor unit reestablishes many of its properties despite marked changes to the composition of the unit brought about by partial denervation. In addition, a reduction in the neuromuscular activity of units during reorganization had a limited effect on recovery.

Animals↗

PubMed1992

Influence of electrical stimulation on the morphological and metabolic properties of paralyzed muscle.

Selected morphological and metabolic properties of single fibers were studied in biopsy samples from the tibialis anterior of normal control and spinal cord-injured (SCI) subjects. In the SCI subjects, one muscle was electrically stimulated progressively over 24 wk, in 6-wk blocks for less than or equal to 8 h/day, while the contralateral muscle remained untreated. The percentage of fibers classified as type I [qualitative alkaline preincubation myofibrillar adenosinetriphosphatase (ATPase)] was significantly less in the unstimulated paralyzed muscles than in the muscles of normal control subjects. Electrical stimulation increased the proportion of type I fibers in the SCI subjects. For both type I and type II fibers, the cross-sectional area, activities of myofibrillar ATPase and succinate dehydrogenase, and the capillary-to-fiber ratio were also significantly less in the paralyzed muscles than in the normal control muscles. Electrical stimulation increased only the activity of succinate dehydrogenase in both fiber types of the SCI subjects. These data are discussed in relation to the electromechanical properties of the respective muscles described in an accompanying paper (J. Appl. Physiol. 72: 1393-1400, 1992). In general, the electrical stimulation protocol used in this study enhanced the oxidative capacity and endurance properties of the paralyzed muscles but had no effect on fiber size and strength.

Adenosine Triphosphatases↗

PubMed1992

Altered distribution of mitochondria in rat soleus muscle fibers after spaceflight.

The influence of spaceflight on the distribution of succinate dehydrogenase (SDH) activity throughout the cross section of fibers in the soleus was studied in five male rats and in five rats maintained under ground-based simulated flight conditions (control). The flight (COSMOS 1887) was 12.5 days in duration, and the animals were killed approximately 2 days after return to 1 G. Fibers were classified as slow-twitch oxidative or fast-twitch oxidative-glycolytic in histochemically prepared tissue sections. The distribution of SDH activity throughout the cross section of 20-30 fibers (each type) was determined using quantitative histochemical and computer-assisted image analysis techniques. In all the fibers, the distribution of SDH activity was significantly higher in the subsarcolemmal than in intermyofibrillar region. After spaceflight the entire regional distribution of SDH activity was significantly altered in the slow-twitch oxidative fibers. The fast-twitch oxidative-glycolytic fibers of the spaceflight muscles exhibited a significantly lower SDH activity only in their subsarcolemmal region. These data suggest that when determining the influence of spaceflight on muscle fiber oxidative metabolism enzymes, it is important to consider the location of the enzyme throughout the cross section of a fiber. Furthermore the functional properties of the soleus that depend on the metabolic support of mitochondria in the subsarcolemmal region may be primarily affected by exposure to microgravity.

Animals↗

PubMed1992

GABAergic inhibition of endogenous dopamine release measured in vivo with 11C-raclopride and positron emission tomography.

Extensive neuroanatomical, neurophysiological, and behavioral evidence demonstrates that GABAergic neurons inhibit endogenous dopamine release in the mammalian corpus striatum. Positron emission tomography (PET) studies in adult female baboons, using the dopamine D2-specific radiotracer 11C-raclopride, were undertaken to assess the utility of this imaging technique for measuring these dynamic interactions in vivo. 11C-raclopride binding was imaged prior to and following the administration of either gamma-vinyl-GABA (GVG), a specific suicide inhibitor of the GABA-catabolizing enzyme GABA transaminase, or lorazepam, a clinically prescribed benzodiazepine agonist. Striatal 11C-raclopride binding increased following both GVG and lorazepam administration. This increase exceeded the test/retest variability of 11C-raclopride binding observed in the same animals. These findings confirm that changes in endogenous dopamine concentrations resulting from drug-induced potentiation of GABAergic transmission can be measured with PET and 11C-raclopride. Finally, this new strategy for noninvasively evaluating the functional integrity of neurophysiologically linked transmitter systems with PET supports its use as an approach for assessing the multiple mechanisms of drug action and their consequences in the human brain.

Aminocaproates↗

PubMed1992

Mechanism of cerebral vasospasm following subarachnoid hemorrhage in monkeys.

This paper reviews our recent studies on the mechanism of cerebral vasospasm following subarachnoid hemorrhage (SAH) in monkeys. Middle cerebral artery (MCA) vasospasm was maximal at 7 days, resolving by 14 days, and absent at 28 days after SAH. Arterial fibrosis was not detected during vasospasm, although there was intimal hyperplasia with fibrosis 28 days after SAH. On scanning electron microscopy, smooth muscle cells from vasospastic arteries had corrugated cell membranes and appeared similar to cells contracted pharmacologically, suggesting that vasospastic smooth muscle is contracted. Morphometric analysis of arteries obtained 7 days after SAH showed no significant increases in arterial wall area of vasospastic arteries compared with normal MCAs. The results suggest vasospasm in monkeys is not due to hypertrophy, hyperplasia, or fibrosis in the arterial wall. Vasospasm may be mainly vascular smooth muscle contraction, which damages the arterial wall, leading to secondary structural changes in the arterial wall which occur after angiographic vasospasm.

Animals↗

PubMed1991

Morphometric analysis of monkey cerebral arteries exposed in vivo to whole blood, oxyhemoglobin, methemoglobin, and bilirubin.

Whether vasospasm results from smooth muscle contraction or from arterial wall infiltration by cells and other material is subject to debate. Computer-assisted image analysis was used to measure lumen area, total wall area, and area of tunica media plus tunica intima of cross-sections of monkey right middle cerebral arteries (MCAs), exposed in vivo for 6 days to whole blood (n = 4), oxyhemoglobin (OxyHb, n = 5), methemoglobin (MetHb, n = 5), bilirubin (n = 5), mock cerebrospinal fluid (CSF, n = 6), and supernatant fluid from an incubated mixture of autologous blood and mock CSF (n = 5). Five control (left) MCAs from each group and 4 MCAs contracted in vitro with potassium chloride were measured. Significant angiographic vasospasm occurred in groups receiving whole blood, supernatant fluid, and OxyHb (p less than 0.05). There was significant correlation (r = 0.58, p less than 0.05) between right MCA diameter on angiography and diameter calculated from lumen area. When compared to effects of mock CSF, OxyHb significantly increased total wall area. When right and left MCAs were compared within groups, total wall area increased in every group with significant increases in groups exposed to mock CSF, OxyHb, and bilirubin (p less than 0.05). No changes developed in area of tunica media plus tunica intima, whether comparing right versus left MCAs within groups or right MCAs between groups. Contraction in vitro did not significantly increase total wall area or area of tunica media plus tunica intima. Light microscopy demonstrated inflammatory debris in the tunica adventitia of arteries from every group. This study shows that whole blood, OxyHb, and supernatant fluid, which contains OxyHb, cause vasospasm. Increases in total wall area are not sufficient to account for luminal narrowing, and therefore, changes such as cell proliferation and arterial wall fibrosis in the intima or media apparently do not contribute primarily to arterial narrowing of vasospasm but could be related to persistence of narrowing. Vessel wall thickening, which does occur, is caused by increased tunica adventitia area only and is nonspecific in that it develops after injection of substances not associated with vasospasm. The data are consistent with the hypothesis that oxyHb causes vasospasm (both angiographic and morphologic) by inducing muscle contraction in the media.

Animals↗

PubMed1991

The influence of functional electrical stimulation on the properties of vastus lateralis fibres following total knee arthroplasty.

The influence of functional electrical muscle stimulation (FES) on selected properties of vastus lateralis muscle fibres was studied in patients recovering from total knee arthroplasty for osteoarthritis. Prior to surgery, on the average, muscle biopsies from the vastus lateralis could be characterized as having a predominance of Type I fibres which were significantly larger in cross-sectional area than the Type II fibres in the same sample. Following surgery, muscle biopsies from a group of patients (n = 7) which received continuous passive motion and no FES, exhibited a marked increase in the proportion of Type II fibres along with a general atrophy of both the Type I and Type II fibres. Patients receiving passive motion and FES (n = 9) also showed an increase in the relative percentage of Type II fibres. Post-operatively, however, there was no significant reduction in fibre area in the stimulated muscles. These data suggest that FES was effective in attenuating the muscle atrophy associated with total knee arthroplasty but had no influence on those metabolic properties which were related to muscle fibre type classification criteria.

Aged↗

PubMed1990

Metabolic and morphologic properties of single muscle fibers in the rat after spaceflight, Cosmos 1887.

The adaptation of a slow (soleus, Sol) and a fast (medial gastrocnemius, MG) skeletal muscle to spaceflight was studied in five young male rats. The flight period was 12.5 days and the rats were killed approximately 48 h after returning to 1 g. Five other rats that were housed in cages similar to those used by the flight rats were maintained at 1 g for the same period of time to serve as ground-based controls. Fibers were classified as dark or light staining for myosin adenosine triphosphatase (ATPase). On the average, the fibers in the Sol of the flight rats atrophied twice as much as those in the MG. Further, the fibers located in the deep (close to the bone and having the highest percentage of light ATPase and high oxidative fibers in the muscle cross section) region of the MG atrophied more than the fibers located in the superficial (away from the bone and having the lowest percentage of light ATPase and high oxidative fibers in the muscle cross-section) region of the muscle. Based on quantitative histochemical assays of single muscle fibers, succinate dehydrogenase (SDH) activity per unit volume was unchanged in fibers of the Sol and MG. However, in the Sol, but not the MG, the total amount of SDH activity in a 10-microns-thick section of a fiber decreased significantly in response to spaceflight. Based on population distributions, it appears that the alpha-glycerophosphate dehydrogenase (GPD) activities were elevated in the dark ATPase fibers in the Sol, whereas the light fibers in the Sol and both fiber types in the MG did not appear to change. The ratio of GPD to SDH activities increased in the dark (but not light) fibers of the Sol and was unaffected in the MG. Immunohistochemical analyses indicate that approximately 40% of the fibers in the Sol of flight rats expressed a fast myosin heavy chain compared with 22% in control rats. Further, 31% of the fibers in the Sol of flight rats expressed both fast and slow myosin heavy chains compared with 8% in control rats. Immunohistochemical changes in the MG were minimal. These data suggest that the magnitude and direction of enzymatic activity and cell volume changes are dependent on the muscle, the region of the muscle, and the type of myosin expressed in the fibers. Further, the ability of fibers to maintain normal or even elevated activities per unit volume of some metabolic enzymes is remarkable considering the marked and rapid decrease in fiber volume.

Adenosine Triphosphatases↗

PubMed1990

Incomplete normalization of dog gracilis muscle grafts with neurovascular repair despite long-term recovery.

Skeletal muscle grafts performed with neurovascular repair are used extensively in clinical situations. However, most controlled experimental studies on the efficacy of such grafts have been conducted on muscles with a relatively small mass and over a limited recovery period. Therefore, selected cellular and matrix component properties of the comparatively large dog gracilis muscle (75 g) were studied 9-12 mo after orthotopic neurovascular grafting. The grafted muscle wet weights were 71% of the contralateral control (sham-operated) muscles. In addition, the concentrations of noncollagenous protein (13%), DNA (28%), and RNA (34%) were significantly reduced in the grafts. However, the concentration of collagen was significantly higher (41%) in the grafts. In this regard, the type III collagen phenotype showed the greatest relative increase. There was no difference between the grafted and control proteoglycan concentration. The metabolic profiles of the grafted muscles were significantly different from control. The activities of myofibrillar adenosinetriphosphatase (34%) and alpha-glycerophosphate dehydrogenase (25%) were reduced, whereas citrate synthase remained unchanged. These data suggest that recovery of up to 1 yr was insufficient for the normalization of several connective tissue matrix components and biochemical properties of the grafts.

Adenosine Triphosphatases↗

PubMed1990

Distribution of muscle fiber types and EMG activity in cat intercostal muscles.

The electromyogram (EMG) activity and histochemical properties of intercostal muscles in the anesthetized cat were studied. The parasternal muscles were consistently active during inspiration. The external intercostals in the rostral spaces and the ventral portions of the midthoracic spaces were also recruited during inspiration. The remaining external intercostals were typically silent, regardless of the level of respiratory drive. The internal intercostal muscles located in the caudal spaces were occasionally recruited during expiration. There was a clear correlation between recruitment patterns of the intercostals and the histochemically defined fiber type properties of the muscles. Intercostal muscles that were routinely recruited during inspiration had a significantly higher proportion of slow-oxidative muscle fibers.

Animals↗

PubMed1988

Protein and collagen content of rat skeletal muscle following space flight.

Biochemical determinations of non-collagenous protein and hydroxyproline were made on rat skeletal muscles following 7 days of space flight aboard the NASA space shuttle mission SL-3. Relative to ground-based controls, the wet weight of each experimental muscle was significantly reduced. This was concomitant with a reduction in non-collagenous protein in the muscles. Protein concentration, however, was reduced only in slow-twitch muscles. The effect of space flight on the concentration and hydroxyproline content was different among the muscles. As a result, the loss of muscle mass in some muscles was the consequence of a reduction in both collagenous and non-collagenous proteins, while in others it was primarily the result of a non-collagenous protein loss.

Animals↗

PubMed1988

Metabolic and fiber size properties of cat tibialis anterior motor units.

The variability among single muscle fiber enzymatic activities and fiber size within a motor unit was studied in the cat tibialis anterior (TA) muscle. Fourteen units were isolated for physiological testing using standard ventral root filament stimulation techniques, and the muscle fibers of these units were identified by glycogen depletion. The cross-sectional areas, succinate dehydrogenase (SDH) and alpha-glycerolphosphate dehydrogenase (GPD) activities, and the relative alkaline myofibrillar adenosine triphosphate staining densities of a sample of glycogen-depleted and -nondepleted muscle fibers were determined using quantitative histochemical techniques. Each of the unit types previously identified to be present in the TA, based on physiological criteria, were represented by the sample population. The variability among the fibers of a unit was significantly more than the variability among repeated measures on a single fiber for cross-sectional area and SDH and GPD activities. The mean coefficients of variation for SDH and GPD activity within motor unit fibers were 29 and 56%, respectively, whereas the variability between fibers of different units within a muscle was significantly greater (53 and 69%, respectively). Additionally, the mean coefficient of variation for cross-sectional area among motor unit fibers was less than that among fibers not depleted of glycogen (25 vs. 46%). These data suggest that although there is clear evidence for some level of neural control of the properties of a muscle unit (variation within a unit was less than the variation across units), this control is not complete, since the variability among fibers of a single unit was significantly more than the variability found between repeated measurements on a single fiber.

Animals↗

PubMed1988

Coordination of electromechanical and metabolic properties of cat soleus motor units.

Motor units were studied in the soleus muscle of normal adult cats and adult cats that had undergone complete spinal cord transection approximately 4 mo earlier. Intracellular recording and stimulation techniques were used to study selected electrical properties of the motoneuron and isometric contractile properties of the muscle unit. Motor unit fibers were depleted of their glycogen through repetitive stimulation of the motoneuron and identified by a quantitative histochemical determination of glycogen. A sample of muscle fibers from the glycogen-depleted unit and from fibers not depleted of glycogen were analyzed for cross-sectional area, succinate dehydrogenase (SDH), alpha-glycerolphosphate dehydrogenase (GPD), and alkaline myofibrillar adenosine triphosphatase. It was observed that the fiber-to-fiber variability in cross-sectional area and SDH and GPD activity within units of normal and transected cats was significantly larger than that measured in repeated samples from a single fiber. Additionally, for each of these properties, the range found among fibers within a unit was similar to that found among nondepleted fibers of the same myosin type. The influence of spinal cord transection on some muscle fibers seemed to result in a metabolic shift from the generalized category of slow-oxidative toward fast-oxidative glycolytic. This shift in metabolic properties appeared to be coupled with a similar shift in the physiological properties of the muscle unit and motoneuron from slow to fast.

Animals↗

PubMed1988

Influence of spaceflight on rat skeletal muscle.

The size, succinate dehydrogenase (SDH) and alpha-glycerolphosphate dehydrogenase (GPD) activities, and alkaline myofibrillar adenosinetriphosphatase (ATPase) staining properties were determined from quantitative histochemical analyses of single fibers from five hindlimb muscles of six male rats exposed to a 7-day National Aeronautics and Space Administration spaceflight mission (SL-3). These same properties were determined in a group of ground-based control rats housed under simulated environmental conditions. The wet weight of each of the flight muscles was significantly reduced relative to control. However, the loss of mass varied from 36% in the soleus to 15% in the extensor digitorum longus. The cross-sectional areas of fibers in the flight muscles also were reduced, except for the dark ATPase fibers in the medial gastrocnemius. The greatest relative fiber atrophy occurred in the muscles with the highest proportion of light ATPase fibers. An increase in the percentage of dark ATPase fibers also was observed in flight muscles with a predominance of light ATPase fibers. Also, there was an increase in the biochemically determined myofibrillar ATPase activity of tissue sections of the flight soleus. No changes in histochemical or biochemical measures of ATPase activity were observed in the flight extensor digitorum longus. In general, the SDH activity of flight muscles was maintained, whereas GPD activity either was maintained or increased. Based on a metabolic profile of ATPase, SDH, and GPD, there was an increase in the proportion of fast oxidative-glycolytic fibers in some muscles.

Adenosine Triphosphatases↗

PubMed1987

Predictable adaptations by skeletal muscle mitochondria to different exercise training workloads.

1. Mitochondria were isolated according to their cellular location within the fibers of pooled gastrocnemius and plantaris muscle of the rat. This procedure yields two populations of mitochondria which display different biochemical properties. 2. The adaptive response of these mitochondria populations to the chronic exposure to different elevated energy demands (different modes of exercise training) was investigated. 3. The observed changes in mitochondrial protein content and cytochrome oxidase activity in the respective mitochondria population suggests that each population is capable of independent adaptations. 4. The adaptive response of each mitochondria population, furthermore, was predictable with respect to the metabolic energy demand of the exercise training workload.

Acclimatization↗

PubMed1986

Model for microneurovascular muscle transplantation in the dog.

Previous studies have suggested that successful transplantation of skeletal muscle to replace previously lost function depends on the mass of the transplanted tissue. In the present experiment, the possibility that careful microneurovascular surgical technique substantially improves the chances of successful transplantation of large-sized muscle was tested using dog gracilis muscle averaging 75 gm in weight. Gracilis muscles were completely excised ipsilaterally and were implanted into their original location (orthotopic) by reattaching tendons of insertion and origin. In addition, neurorrhaphies of nerve stumps were performed along with repair of the vascular pedicle using microsurgery techniques. After approximately 1 year, orthotopic transplants weighed about 70 percent of contralateral sham-operated gracilis muscles. Although average tension output of transplants declined to about 60 percent of control values, three of the most successfully transplanted muscles produced between 73 and 88 percent of control force. A significant increase in the number of slow-twitch-oxidative fibers was correlated with a slight but significant reduction in the maximal velocity of shortening of transplanted muscles. The ability of transplants to resist fatigue when repetitively stimulated was similar to the endurance capacity of control muscles. These results suggest that microneurovascular surgery may enhance the more complete restoration of function of transplanted skeletal muscles of relatively large size.

Adenosine Triphosphatases↗