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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Dietary fat intake, supplements, and weight loss

Although there remains controversy regarding the role of macronutrient balance in the etiology of obesity, the consumption of high-fat diets appears to be strongly implicated in its development. Evidence that fat oxidation does not adjust rapidly to acute increases in dietary fat, as well as a decreased capacity to oxidize fat in the postprandial state in the obese, suggest that diets high in fat may lead to the accumulation of fat stores. Novel data is also presented suggesting that in rodents, high-fat diets may lead to the development of leptin resistance in skeletal muscle and subsequent accumulations of muscle triacylglycerol. Nevertheless, several current fad diets recommend drastically reduced carbohydrate intake, with a concurrent increase in fat content. Such recommendations are based on the underlying assumption that by reducing circulating insulin levels, lipolysis and lipid oxidation will be enhanced and fat storage reduced. Numerous supplements are purported to increase fat oxidation (carnitine, conjugated linoleic acid), increase metabolic rate (ephedrine, pyruvate), or inhibit hepatic lipogenesis (hydroxycitrate). All of these compounds are currently marketed in supplemental form to increase weight loss, but few have actually been shown to be effective in scientific studies. To date, there is little or no evidence supporting that carnitine or hydroxycitrate supplementation are of any value for weight loss in humans. Supplements such as pyruvate have been shown to be effective at high dosages, but there is little mechanistic information to explain its purported effect or data to indicate its effectiveness at lower dosages. Conjugated linoleic acid has been shown to stimulate fat utilization and decrease body fat content in mice but has not been tested in humans. The effects of ephedrine, in conjunction with methylxanthines and aspirin, in humans appears unequivocal but includes various cardiovascular side effects. None of these compounds have been tested for their effectiveness or safety over prolonged periods of time.

NASA Discipline Musculoskeletal↗
NASA NTRS2001

Know thy neighbor: stromal cells can contribute oncogenic signals

Although the stroma within carcinogenic lesions is known to be supportive and responsive to tumors, new data increasingly show that the stroma also has a more active, oncogenic role in tumorigenesis. Stromal cells and their products can transform adjacent tissues in the absence of pre-existing tumor cells by inciting phenotypic and genomic changes in the epithelial cells. The oncogenic action of distinctive stromal components has been demonstrated through a variety of approaches, which provide clues about the cellular pathways involved.

Review↗
NASA NTRS2000

Determination of left ventricular volume, ejection fraction, and myocardial mass by real-time three-dimensional echocardiography

Reconstructed three-dimensional (3-D) echocardiography is an accurate and reproducible method of assessing left ventricular (LV) functions. However, it has limitations for clinical study due to the requirement of complex computer and echocardiographic analysis systems, electrocardiographic/respiratory gating, and prolonged imaging times. Real-time 3-D echocardiography has a major advantage of conveniently visualizing the entire cardiac anatomy in three dimensions and of potentially accurately quantifying LV volumes, ejection fractions, and myocardial mass in patients even in the presence of an LV aneurysm. Although the image quality of the current real-time 3-D echocardiographic methods is not optimal, its widespread clinical application is possible because of the convenient and fast image acquisition. We review real-time 3-D echocardiographic image acquisition and quantitative analysis for the evaluation of LV function and LV mass.

NASA Discipline Cardiopulmonary↗
NASA NTRS2001

Extracellular calcium sensing and extracellular calcium signaling

The cloning of a G protein-coupled extracellular Ca(2+) (Ca(o)(2+))-sensing receptor (CaR) has elucidated the molecular basis for many of the previously recognized effects of Ca(o)(2+) on tissues that maintain systemic Ca(o)(2+) homeostasis, especially parathyroid chief cells and several cells in the kidney. The availability of the cloned CaR enabled the development of DNA and antibody probes for identifying the CaR's mRNA and protein, respectively, within these and other tissues. It also permitted the identification of human diseases resulting from inactivating or activating mutations of the CaR gene and the subsequent generation of mice with targeted disruption of the CaR gene. The characteristic alterations in parathyroid and renal function in these patients and in the mice with "knockout" of the CaR gene have provided valuable information on the CaR's physiological roles in these tissues participating in mineral ion homeostasis. Nevertheless, relatively little is known about how the CaR regulates other tissues involved in systemic Ca(o)(2+) homeostasis, particularly bone and intestine. Moreover, there is evidence that additional Ca(o)(2+) sensors may exist in bone cells that mediate some or even all of the known effects of Ca(o)(2+) on these cells. Even more remains to be learned about the CaR's function in the rapidly growing list of cells that express it but are uninvolved in systemic Ca(o)(2+) metabolism. Available data suggest that the receptor serves numerous roles outside of systemic mineral ion homeostasis, ranging from the regulation of hormonal secretion and the activities of various ion channels to the longer term control of gene expression, programmed cell death (apoptosis), and cellular proliferation. In some cases, the CaR on these "nonhomeostatic" cells responds to local changes in Ca(o)(2+) taking place within compartments of the extracellular fluid (ECF) that communicate with the outside environment (e.g., the gastrointestinal tract). In others, localized changes in Ca(o)(2+) within the ECF can originate from several mechanisms, including fluxes of calcium ions into or out of cellular or extracellular stores or across epithelium that absorb or secrete Ca(2+). In any event, the CaR and other receptors/sensors for Ca(o)(2+) and probably for other extracellular ions represent versatile regulators of numerous cellular functions and may serve as important therapeutic targets.

Review↗
NASA NTRS2000

Developmental evolutionary biology of the vertebrate ear: conserving mechanoelectric transduction and developmental pathways in diverging morphologies

This brief overview shows that a start has been made to molecularly dissect vertebrate ear development and its evolutionary conservation to the development of the insect hearing organ. However, neither the patterning process of the ear nor the patterning process of insect sensory organs is sufficiently known at the moment to provide more than a first glimpse. Moreover, hardly anything is known about otocyst development of the cephalopod molluscs, another triploblast lineage that evolved complex 'ears'. We hope that the apparent conserved functional and cellular components present in the ciliated sensory neurons/hair cells will also be found in the genes required for vertebrate ear and insect sensory organ morphogenesis (Fig. 3). Likewise, we expect that homologous pre-patterning genes will soon be identified for the non-sensory cell development, which is more than a blocking of neuronal development through the Delta/Notch signaling system. Generation of the apparently unique ear could thus represent a multiplication of non-sensory cells by asymmetric and symmetric divisions as well as modification of existing patterning process by implementing novel developmental modules. In the final analysis, the vertebrate ear may come about by increasing the level of gene interactions in an already existing and highly conserved interactive cascade of bHLH genes. Since this was apparently achieved in all three lineages of triploblasts independently (Fig. 3), we now need to understand how much of the morphogenetic cascades are equally conserved across phyla to generate complex ears. The existing mutations in humans and mice may be able to point the direction of future research to understand the development of specific cell types and morphologies in the formation of complex arthropod, cephalopod, and vertebrate 'ears'.

Non-NASA Center↗
NASA NTRS1998

Morphogenesis by symbiogenesis

Here we review cases where initiation of morphogenesis, including the differentiation of specialized cells and tissues, has clearly evolved due to cyclical symbiont integration. For reasons of space, our examples are drawn chiefly from the plant, fungal and bacterial kingdoms. Partners live in symbioses and show unique morphological specializations that result when they directly and cyclically interact. We include here brief citations to relevant literature where plant, bacterial or fungal partners alternate independent with entirely integrated living. The independent, or at least physically unassociated stages, are correlated with the appearance of distinctive morphologies that can be traced to the simultaneous presence and strong interaction of the plant with individuals that represent different taxa.

Review↗
NASA NTRS2000

Dose limits for astronauts

Radiation exposures to individuals in space can greatly exceed natural radiation exposure on Earth and possibly normal occupational radiation exposures as well. Consequently, procedures limiting exposures would be necessary. Limitations were proposed by the Radiobiological Advisory Panel of the National Academy of Sciences/National Research Council in 1970. This panel recommended short-term limits to avoid deterministic effects and a single career limit (of 4 Sv) based on a doubling of the cancer risk in men aged 35 to 55. Later, when risk estimates for cancer had increased and were recognized to be age and sex dependent, the NCRP, in Report No. 98 in 1989, recommended a range of career limits based on age and sex from 1 to 4 Sv. NCRP is again in the process of revising recommendations for astronaut exposure, partly because risk estimates have increased further and partly to recognize trends in limiting radiation exposure occupationally on the ground. The result of these considerations is likely to be similar short-term limits for deterministic effects but modified career limits.

Review↗
NASA NTRS2000

Radiation measurements in low Earth orbit: U.S. and Russian results

The radiation environment in low-Earth orbital flights is complex. It is strongly influenced by altitude, orbital inclination, time within a given solar cycle, flight duration, and shielding configuration. At any specified shielded location, both primary and secondary particles generated by nuclear interactions of primary particles with spacecraft structure are present. In addition, there are atmospheric secondary albedo protons and neutrons. No single detector can adequately measure this complex radiation field, and measurements of very high linear energy transfer target fragmentation products are particularly difficult. Crew radiation exposure have exclusively been measured using passive thermoluminescent detectors (TLDs). The cosmonaut exposures on the Mir station, uncorrected for the TLD inefficiency and neutron contribution, have varied from a low of 2.43 cGy to a high of 8.70 cGy. These correspond to dose rates of 144 microGy d(-1) to 468 microGy d(-1). These are consistent with rates observed by the D2 ion-chamber. Using the rates measured by the D1 chamber, dose rates under 4 cm of water vary from about 60 microGy d-1 to about 350 microGy d(-1). There is variation of about a factor of two between the dose rates at various locations in the same module. There is also a variation of dose rates of about a factor two between various modules. The highest astronaut dose for a Shuttle flight (STS-82) was 3.205 cGy with a dose rate of 3,221 microGy d(-1). Neutron contribution could be 36 +/- 15% of the astronaut charged particle dose equivalent. East-West asymmetry of dose rate is significant for spacecrafts that fly in an fixed altitude, such as the International Space Station.

NASA Center JSC↗
NASA NTRS2000

Overview of radiation environments and human exposures

Human exposures to ionizing radiation have been vastly altered by developing technology in the last century. This has been most obvious in the development of radiation generating devices and the utilization of nuclear energy. But even air travel has had its impact on human exposure. Human exposure increases with advancing aircraft technology as a result of the higher operating altitudes reducing the protective cover provided by Earth's atmosphere from extraterrestrial radiations. This increase in operating altitudes is taken to a limit by human operations in space. Less obvious is the changing character of the radiations at higher altitudes. The associated health risks are less understood with increasing altitude due to the increasing complexity and new field components found in high-altitude and space operations.

Flight Experiment↗
NASA NTRS2000

Neck afferent involvement in cardiovascular control during movement

It is well established that labyrinth and neck afferent information contributes to the regulation of somatomotor function during movement and changes in posture. There is also convincing evidence that the vestibular system participates in the modulation of sympathetic outflow and cardiovascular function during changes in posture, presumably to prevent orthostatic hypotension. However, the labyrinth organs do not provide any signals concerning body movements with respect to the head. In contrast, the neck receptors, particularly muscle spindles, are well located and suited to provide information about changes in body position with respect to the head and vestibular signals. Studies in the cat suggest that neck afferent information may modulate the vestibulosympathetic reflex responses to head-neck movements. There is some evidence in the cat to suggest involvement of low threshold mechanoreceptors. However, human studies do not indicate that low threshold mechanoreceptors in the neck modulate cardiovascular responses. The human studies are consistent with the studies in the cat in that they demonstrate the importance of otolith activation in mediating cardiovascular and sympathetic responses to changes in posture. This paper briefly reviews the current experimental evidence concerning the involvement of neck afferent information in the modulation of cardiovascular control during movement and changes in posture.

Review↗
NASA NTRS2000

Adaptive plasticity in vestibular influences on cardiovascular control

Data collected in both human subjects and animal models indicate that the vestibular system influences the control of blood pressure. In animals, peripheral vestibular lesions diminish the capacity to rapidly and accurately make cardiovascular adjustments to changes in posture. Thus, one role of vestibulo-cardiovascular influences is to elicit changes in blood distribution in the body so that stable blood pressure is maintained during movement. However, deficits in correcting blood pressure following vestibular lesions diminish over time, and are less severe when non-labyrinthine sensory cues regarding body position in space are provided. These observations show that pathways that mediate vestibulo-sympathetic reflexes can be subject to plastic changes. This review considers the adaptive plasticity in cardiovascular responses elicited by the central vestibular system. Recent data indicate that the posterior cerebellar vermis may play an important role in adaptation of these responses, such that ablation of the posterior vermis impairs recovery of orthostatic tolerance following subsequent vestibular lesions. Furthermore, recent experiments suggest that non-labyrinthine inputs to the central vestibular system may be important in controlling blood pressure during movement, particularly following vestibular dysfunction. A number of sensory inputs appear to be integrated to produce cardiovascular adjustments during changes in posture. Although loss of any one of these inputs does not induce lability in blood pressure, it is likely that maximal blood pressure stability is achieved by the integration of a variety of sensory cues signaling body position in space.

Non-NASA Center↗
NASA NTRS1979

Gravity as a biochemical determinant

The existence of obvious morphological and physiological changes in living systems exposed to altered gravity immediately informs us that prior changes have taken place in the chemistry of exposed cells, tissues and organs. These changes include transients that return more or less promptly to the norm when the system is restored to the terrestrial g-field. For example, altered serum hormone and electrolyte levels in man, which appear to reflect successful adaptation to the conditions of orbital weightlessness, disappear shortly after return to Earth. Other changes--in mineral and protein constituents of the skeletal system in man, and cell wall composition in plants--are more persistent or even permanent. Hypogravitational departures from the norm include not only "weightlessness" as achieved in orbit, but also experimental modes of compensation, on the clinostat or by flotation. These techniques are useful in the study of hypogravity but cannot replace fully the weightless environment. Plant ethylene and peroxidase both increase under orbital, clinostat and/or flotation conditions whereas 3-phosphoglyceraldehyde-dehydrogenase increases under orbital but not clinostat conditions; cytochrome reductase and malic dehydrogenase levels are affected by the clinostat, but not by actual weightless conditions. How do the altered organismal biochemistries induced by the centrifuge and the clinostat relate to one another? Does gravity operate on living systems as a continuous variable from 0 to superterrestrial values, or do deviations from g(earth) generate non-uniform, discontinuous stress responses, irrespective of sign? In plants, measurements of wall lignin content and peroxidase activity yield opposite answers. Given the limited data so far available we will consider the meaning of these contradictions.

Review↗
NASA NTRS1979

A review of the consequences of fluid and electrolyte shifts in weightlessness

This review describes the renal-endocrine mechanisms related to the early losses of fluid-electrolytes from the body during weightlessness as well as their contribution to longer term adaptation of fluid-electrolyte balance. The hypotheses presented were generated by a systematic analysis of body fluid and renal dynamics observed under conditions of actual and simulated spaceflight. These have increased our understanding of the effects of acute headward fluid shifts on renal excretion, the factors promoting excess sodium excretion and the regulation of extracellular fluid composition.

Review↗
NASA NTRS1984

The origin of the eukaryotic cell

The endosymbiotic hypothesis for the origin of the eukaryotic cell has been applied to the origin of the mitochondria and chloroplasts. However as has been pointed out by Mereschowsky in 1905, it should also be applied to the nucleus as well. If the nucleus, mitochondria and chloroplasts are endosymbionts, then it is likely that the organism that did the engulfing was not a DNA-based organism. In fact, it is useful to postulate that this organism was a primitive RNA-based organism. This hypothesis would explain the preponderance of RNA viruses found in eukaryotic cells. The centriole and basal body do not have a double membrane or DNA. Like all MTOCs (microtubule organising centres), they have a structural or morphic RNA implicated in their formation. This would argue for their origin in the early RNA-based organism rather than in an endosymbiotic event involving bacteria. Finally, the eukaryotic cell uses RNA in ways quite unlike bacteria, thus pointing to a greater emphasis of RNA in both control and structure in the cell. The origin of the eukaryotic cell may tell us why it rather than its prokaryotic relative evolved into the metazoans who are reading this paper.

Review↗
NASA NTRS1984

Peptides and neurotransmitters that affect renin secretion

Substance P inhibits renin secretion. This polypeptide is a transmitter in primary afferent neurons and is released from the peripheral as well as the central portions of these neurons. It is present in afferent nerves from the kidneys. Neuropeptide Y, which is a cotransmitter with norepinephrine and epinephrine, is found in sympathetic neurons that are closely associated with and presumably innervate the juxtagolmerular cells. Its effect on renin secretion is unknown, but it produces renal vasoconstriction and natriuresis. Vasoactive intestinal polypeptide (VIP) is a cotransmitter with acetylocholine in cholinergic neurons, and this polypeptide stimulates renin secretion. We cannot find any evidence for its occurence in neurons in the kidneys, but various stimuli increase plasma VIP to levels comparable to those produced by doses of exogenous VIP which stimulated renin secretion. Neostigmine increases plasma VIP and plasma renin activity, and the VIP appears to be responsible for the increase in renin secretion, since the increase is not blocked by renal denervation or propranolol. Stimulation of various areas in the brain produces sympathetically mediated increases in plasma renin activity associated with increases in blood pressure. However, there is pharmacological evidence that the renin response can be separated from the blood pressure response. In anaesthetized dogs, drugs that increase central serotonergic discharge increase renin secretion without increasing blood pressure. In rats, activation of sertonergic neurons in the dorsal raphe nucleus increases renin secretion by a pathway that projects from this nucleus to the ventral hypothalamus, and from there to the kidneys via the sympathetic nervous system. The serotonin releasing drug parachloramphetamine also increases plasma VIP, but VIP does not appear to be the primary mediator of the renin response. There is preliminary evidence that the serotonergic neurons in the dorsal raphe nucleus are part of the pathway by which psychosocial stimuli increase renin secretion.

Review↗
NASA NTRS1985

Early events in geotropism of seedling shoots

Developments during the first ten minutes of geotropic stimulation in plant seedling shoots are reviewed. Topics include induction and curvature; early processes; the relationship between auxin, electric field, calcium, and differential growth; gravity reception leading to Went-Cholodny transport; and comparison of root and shoot. Early processes reviewed are sedimentation of amyloplasts, release of ethylene, rise of electrical and auxin asymmetry, redistribution of calcium, asymmetric vascular transport, increase in tendency to deposit callose, and simulation of putative exocytotic voltage transients.

Review↗
NASA NTRS1989

Periodicity in extinction and the problem of catastrophism in the history of life

The hypothesis that extinction events have recurred periodically over the last quarter billion years is greatly strengthened by new data on the stratigraphic ranges of marine animal genera. In the interval from the Permian to Recent, these data encompass some 13,000 generic extinctions, providing a more sensitive indicator of species-level extinctions than previously used familial data. Extinction time series computed from the generic data display nine strong peaks that are nearly uniformly spaced at 26 Ma intervals over the last 270 Ma. Most of these peaks correspond to extinction events recognized in more detailed, if limited, biostratigraphic studies. These new data weaken or negate most arguments against periodicity, which have involved criticisms of the taxonomic data base, sampling intervals, chronometric time scales, and statistical methods used in previous analyses. The criticisms are reviewed in some detail and various new calculations and simulations, including one assessing the effects of paraphyletic taxa, are presented. Although the new data strengthen the case for periodicity, they offer little new insight into the deriving mechanism behind the pattern. However, they do suggest that many of the periodic events may not have been catastrophic, occurring instead over several stratigraphic stages or substages.

NASA Discipline Number 52-40↗
NASA NTRS1985

Iron and sulfur in the pre-biologic ocean

Tentative geochemical cycles for the pre-biologic Earth are developed by comparing the relative fluxes of oxygen, dissolved iron, and sulfide to the atmosphere and ocean. The flux of iron is found to exceed both the oxygen and the sulfide fluxes. Because of the insolubility of iron oxides and sulfides the implication is that dissolved iron was fairly abundant and that oxygen and sulfide were rare in the atmosphere and ocean. Sulfate, produced by the oxidation of volcanogenic sulfur gases, was the most abundant sulfur species in the ocean, but its concentration was low by modern standards because of the absence of the river-borne flux of dissolved sulfate produced by oxidative weathering of the continents. These findings are consistent with the geologic record of the isotopic composition of sedimentary sulfates and sulfides. Except in restricted environments, the sulfur metabolism of the earliest organisms probably involved oxidized sulfur species not sulfide.

Review↗