Engineering topics

Tischler, Marc E.

Publications and source records attributed to Tischler, Marc E..

At least 19 records

NASA NTRS2002

Differential half-maximal effects of human insulin and its analogs for in situ glucose transport and protein synthesis in rat soleus muscle

Analogs of human insulin have been used to discriminate between responses of metabolic and mitogenic (growth-related) pathways. This study compared the stimulatory effects of human insulin (HI) and 2 analogs (X2, B-Asp(9), B-Glu(27) and H2, A-His(8),B-His(4),B-Glu(10), B-His(27)) on glucose uptake and protein synthesis in rat soleus muscle in situ. Glucose uptake, estimated by intramuscular (IM) injection of 2-deoxy[1,2-3H]glucose with or without insulin, was maximally increased at 10(-6) mol/L for HI and X2 and 10(-7) mol/L for H2. HI had a larger effect (318%) than either X2 (156%) or H2 (124%). The half-maximal effect (ED(50)) values for HI, X2, and H2 were 3.3 x10(-8) mol/L, 1.7 x 10(-7) mol/L, and 1.6 x 10(-9) mol/L, respectively. Protein synthesis, estimated by protein incorporation of [(3)H]phenylalanine injected into muscles with or without insulin, was maximally increased at 10(-5) mol/L for HI and 10(-6) for X2 and H2. HI had a larger effect in stimulating protein synthesis (34%) than either X2 (25%) or H2 (19.8%). The ED(50) values for HI, X2, and H2 were 3.0 x 10(-7) mol/L, 3.2 x 10(-7) mol/L, and 1.0 x 10(-9) mol/L, respectively. The biological potency of each analog (ED(50)insulin/ED(50)analog) showed X2 to be less potent than HI for both glucose uptake (0.2) and protein synthesis (0.9), whereas H2 is more potent than HI with ratios of 20 and 300, respectively. These data suggest that this approach for studying insulin responsiveness in a single muscle in situ may be a useful tool for investigating insulin signaling in muscle in vivo. Copyright 2002, Elsevier Science (USA). All rights reserved.

NASA Discipline Developmental Biology↗

NASA NTRS2002

Influence of Unweighting on Insulin Signal Transduction in Muscle

Unweighting of the juvenile soleus muscle is characterized by an increased binding capacity for insulin relative to muscle mass due to sparing of the receptors during atrophy. Although carbohydrate metabolism and protein degradation in the unweighted muscle develop increased sensitivity to insulin in vivo, protein synthesis in vivo and system A amino acid transport in vitro do not appear to develop such an enhanced response. The long-term goal is to identify the precise nature of this apparent resistance in the insulin signal transduction pathway and to consider how reduced weight-bearing may elicit this effect, by evaluating specific components of the insulin signalling pathway. Because the insulin-signalling pathway has components in common with the signal transduction pathway for insulin-like growth factor (IGF-1) and potentially other growth factors, the study could have important implications in the role of weight-bearing function on muscle growth and development. Since the insulin signalling pathway diverges following activation of insulin receptor tyrosine kinase, the immediate specific aims will be to study the receptor tyrosine kinase (IRTK) and those branches, which lead to phosphorylation of insulin receptor substrate-1 (IRS-1) and of Shc protein. To achieve these broader objectives, we will test in situ, by intramuscular injection, the responses of glucose transport, system A amino acid transport and protein synthesis to insulin analogues for which the receptor has either a weaker or much stronger binding affinity compared to insulin. Studies will include: (1) estimation of the ED(sub 50) for each analogue for these three processes; (2) the effect of duration (one to four days) of unweighting on the response of each process to all analogues tested; (3) the effect of unweighting and the analogues on IRTK activity; and (4) the comparative effects of unweighting and analogue binding on the tyrosine phosphorylation of IRTK, IRS-1, and Shc protein.

Tischler, Marc E.↗

NASA NTRS1996

Insect Development in Altered Gravitational Environment

When tobacco hornworm (Manduca sexta) larvae burrow underground (25-30 cm) to pupate, they reorient themselves to a relatively horizontal position indicating an ability to sense gravity. To evaluate their sensitivity to gravitational environment during metamorphosis, Manduca (pharate adults) were placed in a vertical (head-up) position. Distinct morphological changes, each one reflecting ensuing phases, were used to follow adult development. Five days after pupation, the vertical group showed accelerated (P less than 0.05) development and were nearly 4 phases ahead (P less than 0.0001) after 10 days. Differences in development in the vertical group were characterized further by increased (7-48%) hemolymph concentrations of 13 amino acids, but a decrease in cys and pro and no change in arg, his, met and val (trp, undetectable). Decreased (36%) turnover of injected H-3 - phenylalanine suggested slower utilization of amino acids contributed, at least partly, to the increased concentrations. Vertically-oriented Manduca also exhibited a greater (20 %, P less than 0.001) protein content in their flight muscles near the end of development. Analysis of hemolymph sugar levels showed a redistribution of sugars from the monosaccharide glucose to the disaccharide trehalose. Since injection of 20-hydroxyecdysone decreased (49%) turnover of H-3- phenylalanine in pharate adults and since ecdysteroids are known to increase flight muscle size and control adult development, these results are consistent with our measuring a greater (+80%, P less than 0.05) ecdysteroid titer in the vertically-oriented insects. These results suggest that gravity environment influences ecdysone output by the pharate adult. When we evaluated hemolymph flow in the head-up and control positions, we found that injected C-14-inulin was distributed somewhat more rapidly in the head-up group irrespective of the sight of injection (head or abdomen) likely because in the head-up position flow of the hemolymph is facilitated throughout the animal. Other experiments showed that an intact prothoracic gland is needed for the response. Hence vertical, head-up orientation affects release of ecdysone from the prothoracic gland.

Tischler, Marc E.↗

NASA NTRS1996

Effect of Altered Gravity Environment on Tobacco Hornworm (Manduca Sexta) Development

Metamorphosis provides a unique condition for studying the role of gravity in development. Formation of new organs in a previously existing organism requires a highly active period of turnover of amino acids and proteins, and of changes in the endocrine profile. Furthermore, metamorphosis offers the advantage of studying a self-contained biological system. The tobacco hornworm provides a suitable species to study the effect of altered gravitational environment on invertebrate development. This species has been one of the most thoroughly investigated organisms in a variety of aspects of insect biology. M. sexta pharate adults can provide significant amounts of material with which to work, thus facilitating the study of metabolic aspects of adult development. During wandering, the period immediately following cessation of larval feeding, the larva burrows into the soil to form a pupation chamber. Despite burrowing down 25 to 30 cm, the insects reorient themselves to a slightly head-up (10 +/- 1 degree) position. Since light and temperature are not factors in this process, the larvae must sense the gravity vector. In our ground-based studies we had assessed whether developing adults might be sensitive to their gravitational environment by orienting pupae in a vertical head-up position within 24 to 48 h after pupal ecdysis. Our ground-based findings formed the foundation for determining which parameters would be evaluated in developing Manduca following spaceflight. Measurements were to include: (1) extent of development by all of the insects, (2) analysis of hemolymph obtained from half of the insects postflight for ecdysteroid, amino acid, urea, ammonia and trehalose concentrations, (3) further development of the other half of the insects to adult (moths), (4) analysis of the flight muscle protein content of the adults. Based on the first flight attempt in July, 1995, we modified the BRIC hardware to accommodate the insects. Our studies after BRIC-04 showed that sealing the top and bottom lids of the canisters with an 0-ring and with vacuum grease caused the insects to stop developing because of accumulation of carbon dioxide. Even though removing both the O-rings and vacuum grease permitted normal development, there was still some increase in carbon dioxide levels. Consequently, the canisters were vented and the vents covered with gas permeable membrane.

Tischler, Marc E.↗

NASA NTRS1993

Space research on organs and tissues

Studies in space on various physiological systems have and will continue to provide valuable information on how they adapt to reduced gravitational conditions, and how living in a 1 g (gravity) environment has guided their development. Muscle and bone are the most notable tissues that respond to unweighting caused by lack of gravity. The function of specific muscles and bones relates directly to mechanical loading, so that removal of 'normal forces' in space, or in bedridden patients, causes dramatic loss of tissue mass. The cardiovascular system is also markedly affected by reduced gravity. Adaptation includes decreased blood flow to the lower extremities, thus decreasing the heart output requirement. Return to 1 g is associated with a period of reconditioning due to the deconditioning that occurs in space. Changes in the cardiovascular system are also related to responses of the kidney and certain endocrine (hormone-producing) organs. Changes in respiratory function may also occur, suggesting an effect on the lungs, though this adaptation is poorly understood. The neurovestibular system, including the brain and organs of the inner ear, must adapt to the disorientation caused by lack of gravity. Preliminary findings have been reported for liver. Additionally, endocrine organs responsible for release of hormones such as insulin, growth hormone, glucocorticoids, and thyroid hormone may respond to spaceflight.

Tischler, Marc E.↗

NASA NTRS1993

Time Course of the Response of Myofibrillar and Sarcoplasmic Protein Metabolism to Unweighting of the Soleus Muscle

Contributions of altered in vivo protein synthesis and degradation to unweighting atrophy of the soleus muscle in tail-suspended young female rats were analyzed daily for up to 6 days. Specific changes in myofibrillar and sarcoplasmic proteins were also evaluated to assess their contributions to the loss of total protein. Synthesis of myofibrillar and sarcoplasmic proteins was estimated by intramuscular (IM) injection and total protein by intraperitoneal (IP) injection of flooding doses of H-3-phenylaianine. Total protein loss was greatest during the first 3 days following suspension and was a consequence of the loss of myofibrillar rather than sarcoplasmic proteins. However, synthesis of total myofibrillar and sarcoplasmic proteins diminished in parallel beginning in the first 24 hours. Therefore sarcoplasmic proteins must be spared due to a decrease in their degradation. In contrast, myofibrillar protein degradation increased, thus explaining the elevated degradation of the total pool. Following 72 hours of suspension, protein synthesis remained low, but the rate of myofibrillar protein loss diminished, suggesting a slowing of degradation. These various results show acute loss of protein during unweighting atrophy is a consequence of decreased synthesis and increased degradation of myofibrillar proteins, and sarcoplasmic proteins are spared due to slower degradation, likely explaining the sparing of plasma membrane receptors. Based on other published data, we propose that the slowing of atrophy after the initial response may be attributed to an increased effect of insulin.

Munoz, Kathryn A.↗

NASA NTRS1993

Spaceflight on STS-48 and earth-based unweighting produce similar effects on skeletal muscle of young rats

Eight female albino rats were exposed to 5.4 days of weightlessness aboard the Space Shuttle mission STS-48 in 1991. An asynchronous ground control experiment mimicked the flight cage conditions and mission duration of the STS-48 rats, and a third group of animals underwent limb suspension for 5.4 days. The flight animals gained a greater percentage of body mass per day despite similar rates of food consumption in the three groups. The results obtained on insulin response and muscle size show that a tail-cast hindlimb-suspension model is suitable for mimicking the effects of weightlessness on rapidly growing juvenile rat muscles.

Tischler, Marc E.↗

NASA NTRS1993

Skeletal muscle metabolism in hypokinetic rats

This grant focused on the mechanisms of metabolic changes associated with unweighting atrophy and reduced growth of hind limb muscles of juvenile rats. Metabolic studies included a number of different areas. Amino acid metabolic studies placed particular emphasis on glutamine and branched-chain amino acid metabolism. These studies were an outgrowth of understanding stress effects and the role of glucocorticoids in these animals. Investigations on protein metabolism were largely concerned with selective loss of myofibrillar proteins and the role of muscle proteolysis. These investigations lead to finding important differences from denervation and atrophy and to define the roles of cytosolic versus lysosomal proteolysis in these atrophy models. A major outgrowth of these studies was demonstrating an ability to prevent atrophy of the unweighted muscle for at least 24 hours. A large amount of work concentrated on carbohydrate metabolism and its regulation by insulin and catecholamines. Measurements focused on glucose transport, glycogen metabolism, and glucose oxidation. The grant was used to develop an important new in situ approach for studying protein metabolism, glucose transport, and hormonal effects which involves intramuscular injection of various agents for up to 24 hours. Another important consequence of this project was the development and flight of Physiological-Anatomical Rodent Experiment-1 (PARE-1), which was launched aboard Space Shuttle Discovery in September 1991. Detailed descriptions of these studies can be found in the 30 peer-reviewed publications, 15 non-reviewed publications, 4 reviews and 33 abstracts (total 82 publications) which were or are scheduled to be published as a result of this project. A listing of these publications grouped by area (i.e. amino acid metabolism, protein metabolism, carbohydrate metabolism, and space flight studies) are included.

Tischler, Marc E.↗

NASA NTRS1992

Cyclic Adenosine Monophosphate Accumulation and beta-Adrenergic Binding in Unweighted and Denervated Rat Soleus Muscle

Unweighting, but not denervation, of muscle reportedly "spares" insulin receptors, increasing insulin sensitivity. Unweighting also increases beta-adrenergic responses of carbohydrate metabolism. These differential characteristics were studied further by comparing cyclic adenosine monophosphate (cAMP) accumulation and beta-adrenergic binding in normal and 3-day unweighted or denervated soleus muscle. Submaximal amounts of isoproterenol, a p-agonist, increased cAMP accumulation in vitro and in vivo (by intramuscular (IM) injection) to a greater degree (P less than .05) in unweighted muscles. Forskolin or maximal isoproterenol had similar in vitro effects in all muscles, suggesting increased beta-adrenergic sensitivity following unweighting. Increased sensitivity was confirmed by a greater receptor density (B(sub max)) for iodo-125(-)-pindolol in particulate preparations of unweighted (420 x 10(exp -18) mol/mg muscle) than of control or denervated muscles (285 x 10(exp-18) mol/mg muscle). The three dissociation constant (Kd) values were similar (20.3 to 25.8 pmol/L). Total binding capacity (11.4 fmol/muscle) did not change during 3 days of unweighting, but diminished by 30% with denervation. This result illustrates the "sparing" and loss of receptors, respectively, in these two atrophy models. In diabetic animals, IM injection of insulin diminished CAMP accumulation in the presence of theophylline in unweighted muscle (-66% +/- 2%) more than in controls (-42% +'- 6%, P less than .001). These results show that insulin affects CAMP formation in muscle, and support a greater in vivo insulin response following unweighting atrophy. These various data support a role for lysosomal proteolysis in denervation, but not in unweighting, atrophy.

Kirby, Christopher R.↗

NASA NTRS1992

Space research on organs and tissues

The effects of microgravity on various physiological systems are reviewed focusing on muscle, bone, cardiovascular, pulmonary, neurovestibular, liver, and endocrine systems. It is noted that certain alterations of organs and tissues caused by microgravity are not reproducible in earth-bound animal or human models. Thus space research on organs and tissues is essential for both validating the earth-bound models used in laboratories and studying the adaptations to weightlessness which cannot be mimicked on earth.

Tischler, Marc E.↗

NASA NTRS1991

Mechanisms of accelerated proteolysis in rat soleus muscle atrophy induced by unweighting or denervation

A hypothesis proposed by Tischler and coworkers (Henriksen et al., 1986; Tischler et al., 1990) concerning the mechanisms of atrophy induced by unweighting or denervation was tested using rat soleus muscle from animals subjected to hindlimb suspension and denervation of muscles. The procedure included (1) measuring protein degradation in isolated muscles and testing the effects of lysosome inhibitors, (2) analyzing the lysosome permeability and autophagocytosis, (3) testing the effects of altering calcium-dependent proteolysis, and (4) evaluating in vivo the effects of various agents to determine the physiological significance of the hypothesis. The results obtained suggest that there are major differences between the mechanisms of atrophies caused by unweighting and denervation, though slower protein synthesis is an important feature common for both.

Tischler, Marc E.↗

NASA NTRS1990

beta-adrenergic effects on carbohydrate metabolism in the unweighted rat soleus muscle

The effect of unweighting on the response of the soleus-muscle carbohydrate metabolism to a beta-adrenergic agonist (isoproterenol) was investigated in rats that were subjected to three days of tail-cast suspension. It was found that isoproterenol promoted glycogen degradation in soleus from suspended rats to a higher degree than in weighted soleus from control rats, and had no effect in unweighted digitorum longus. However, isoproterenol did not have a greater inhibitory effect on the net uptake of tritium-labeled 2-deoxy-glucose by the unweighted soleus and that isoproterenol inhibited hexose phosphorylation less in the unweighted than in the control muscle.

Kirby, Christopher R.↗

NASA NTRS1989

Glycogen supercompensation in rat soleus muscle during recovery from nonweight bearing

Events leading to the normalization of the glycogen metabolism in the soleus muscle of rat, altered by 72-h three days of hind-limb suspension, were investigated during the 72-h recovery period when the animals were allowed to bear weight on all four limbs. Relative importance of the factors affecting glycogen metabolism in skeletal muscle during the recovery period was also examined. Glycogen concentration was found to decrease within 15 min and up to 2 h of recovery, while muscle glucose 6-phosphate, and the fractional activities of glycogen phosphorylase and glycogen synthase increased. From 2 to 4 h, when the glycogen synthase activity remained elevated and the phosphorylase activity declined, glycogen concentration increased, until it reached maximum values at about 24 h, after which it started to decrease, reaching control values by 72 h. At 12 and 24 h, the inverse relationship between glycogen concentration and the synthase activity ratio was lost, indicating that the reloading transiently uncoupled glycogen control of this enzyme.

Henriksen, Erik J.↗

NASA NTRS1989

Effects of stretching and disuse on amino acids in muscles of rat hind limbs

The effects of disuse and passive stretch on the concentrations of amino acids and ammonia in the unloaded soleus muscle was investigated in hindquarter-suspended (for six days by casting one foot in dorsiflexion) tail-casted rats. For a comparison with the condition of unloading, amino acids and ammonia were also measured in shortened extensor digitorum longus in the same casted limb and in denervated leg muscles. The results obtained suggest that passive stretch diminishes some of the characteristic alterations of amino acid concentrations due to unloading. This effect of stretch is considered to be due to the maintenance of muscle tension.

Jaspers, Stephen R.↗

NASA NTRS1989

Metabolism of branched-chain amino acids in leg muscles from tail-cast suspended intact and adrenalectomized rats

The effects of muscle unloading, adrenalectomy, and cortisol treatment on the metabolism of branched-chain amino acids in the soleus and extensor digitorum longus of tail-cast suspended rats were investigated using C-14-labeled lucine, isoleucine, and valine in incubation studies. It was found that, compared to not suspended controls, the degradation of branched-chain amino acids in hind limb muscles was accelerated in tail-cast suspended rats. Adrenalectomy was found to abolish the aminotransferase flux and to diminish the dehydrogenase flux in the soleus. The data also suggest that cortisol treatment increases the rate of metabolism of branched-chain amino acids at the dehydrogenase step.

Jaspers, Stephen R.↗

NASA NTRS1989

Effects of oxygen deprivation on incubated rat soleus muscle

Isolated soleus muscle deprived of oxygen produces more lactate and alanine than oxygen-supplied muscle. Oxygenated muscle synthesized glutamine, while anoxic muscle used this amino acid. Oxygen deprivation decreased adenine nucleotides leading to the efflux of nucleosides. Protein synthesis and degradation responded differently to anoxia. Synthesis almost completely ceased, while proteolysis increased. Therefore, protein degradation in soleus muscle is enhanced when energy supplies and oxygen tension are low.

Fagan, Julie M.↗

NASA NTRS1988

Role of glucocorticoids in increased muscle glutamine production in starvation

The role of glucocorticoids in the synthesis of muscle glutamine during starvation was investigated in adrenalectomized fasted rats injected with cortisol (1 mg/100 g body weight). It was found that administration of cortisol in vivo increased (compared to nontreated starved adrenalectomized controls) the glutamine/glutamate ratio and the activity of glutamine synthetase in the diaphragm and the extensor digitorum muscles, and that these effects were abolished by prior treatment with actinomycin D or proflavine. The results obtained in in vitro experiments, using fresh-frozen soleus, extensor digitorum longus, and diaphragm muscle preparations, supported the in vivo indications of the cortisol-enhanced glutamine synthesis and protein turnover in starved adrenalectomized animals.

Tischler, Marc E.↗

NASA NTRS1988

Effects of immobilization on rat hind limb muscles under non-weight-bearing conditions

The effect of stretched and unstretched immobilization of a hind limb on the concentration and the metabolism of proteins in the hind-limb muscles of rats was investigated. The animals were divided into three groups: (1) weight-bearing controls, (2) tail-cast-suspended, and (3) suspended, with one hind limb immobilized with the ankle in dorsiflexion (30-40 deg angle) and the other freely moving. It was found that unloading the hind limbs for 6 days by tail cast suspension caused soleus to atrophy and reduced growth of the gastrocnemius and plantaris muscles; unloading resulted in a higher degradation rate and lower synthesis rate in both in vitro and in vivo. Chronic stretch of the unloaded soleus not only prevented its atrophy but led to significant hypertrophy, relative to weight-bearing controls, with increases in both the sarcoplasmic and myofibrillar protein fractions. Immobilizing one ankle in dorsiflexion prevented the inhibition of growth in the plantaris and gastrocnemius muscles due to unloading.

Jaspers, Stephen R.↗