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At least 91 records · Page 5

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NASA NTRS1996

Regulation of statoconia mineralization in Aplysia californica in vitro

Statoconia are calcium carbonate inclusions in the lumen of the gravity-sensing organ, the statocyst, of Aplysia californica. The aim of the present study was to examine the role of carbonic anhydrase and urease in statoconia mineralization in vitro. The experiments were performed using a previously described culture system (Pedrozo et al., J. Comp. Physiol. (A) 177:415-425). Inhibition of carbonic anhydrase by acetazolamide decreased statoconia production and volume, while inhibition of urease by acetohydroxamic acid reduced total statoconia number, but had no affect on statoconia volume. Inhibition of carbonic anhydrase initially increased and then decreased the statocyst pH, whereas inhibition of urease decreased statocyst pH at all times examined; simultaneous addition of both inhibitors also decreased pH. These effects were dose and time dependent. The results show that carbonic anhydrase and urease are required for statoconia formation and homeostasis, and for regulation of statocyst pH. This suggests that these two enzymes regulate mineralization at least partially through regulation of statocyst pH.

NASA Discipline Neuroscience↗

NASA NTRS1968

Biology of hard tissue

Conference on bone diseases and regeneration, cellular differentiation, and homeostasis of calcium

Budy, A. M.↗

NASA NTRS1968

A new homeostat

Homeostasis concepts, and design of simple adaptive controller

Wilkins, M. G.↗

NASA NTRS1971

Brain serotonin content - Increase following ingestion of carbohydrate diet.

In the rat, the injection of insulin or the consumption of carbohydrate causes sequential increases in the concentrations of tryptophan in the plasma and the brain and of serotonin in the brain. Serotonin-containing neurons may thus participate in systems whereby the rat brain integrates information about the metabolic state in its relation to control of homeostasis and behavior.

Fernstrom, J. D.↗

NASA NTRS1974

The effect of continuous low dose-rate gamma irradiation on cell population kinetics of lymphoid tissue

Cellular response and cell population kinetics were studied during lymphopoiesis in the thymus of the mouse under continuous gamma irradiation using autoradiographic techniques and specific labeling with tritiated thymidine. On the basis of tissue weights, it is concluded that the response of both the thymus and spleen to continuous low dose-rate irradiation is multiphasic. That is, alternating periods of steady state growth, followed by collapse, which in turn is followed by another period of homeostasis. Since there are two populations of lymphocytes - short lived and long-lived, it may be that different phases of steady state growth are mediated by different lymphocytes. The spleen is affected to a greater extent with shorter periods of steady-state growth than exhibited by the thymus.

Foster, B. R.↗

NASA NTRS1974

Proceedings of the 1972 Lyndon B. Johnson Space Center Endocrine Program Conference

Subjects covered during the Endocrine Program Conference include the following: (1) endocrine/metabolic studies on the Apollo 16 crewmen; (2) changes in glucose, insulin, and growth hormone levels associated with bed rest; (3) circadian rhythms of heart rate and body temperature during 56 days of bed rest; (4) stress-induced changes in corticosteroid metabolism in man; (5) present status of physiological studies on parathyroid hormone and vitamin D; (6) antagonistic effect of lithium on antidiuretic hormone action; (7) proposed Skylab body-fluid volumes study; (8) daily rhythmic changes in serotonin content in areas of the mouse brain and norepinephrine content in areas of the hamster brain; (9) studies of sodium homeostasis during simulated weightlessness; and (10) application of the water immersion model to man.

Source record↗

NASA NTRS1974

Biological modulation of the earth's atmosphere

Review of the evidence that the earth's atmosphere is regulated by life on the surface so that the probability of growth of the entire biosphere is maximized. Acidity, gas composition including oxygen level, and ambient temperature are enormously important determinants for the distribution of life. The earth's atmosphere deviates greatly from that of the other terrestrial planets in particular with respect to acidity, composition, redox potential and temperature history as predicted from solar luminosity. These deviations from predicted steady state conditions have apparently persisted over millions of years. These anomalies may be evidence for a complex planet-wide homeostasis that is the product of natural selection. Possible homeostatic mechanisms that may be further investigated by both theoretical and experimental methods are suggested.

Margulis, L.↗

NASA NTRS1975

Circadian variation of intercompartmental potassium fluxes in man

Circadian rhythms of plasma potassium concentration and urinary potassium excretion persisted in three normal volunteers when diurnal variations in activity, posture, and dietary intake were eliminated for 3-10 days. Measurements of the arteriovenous difference in plasma potassium concentration across the resting forearm and of erythrocyte potassium concentration suggested that there is a net flux of potassium from ICF to ECF in the early morning and a reverse net flux later in the day. The total net ICF-ECF fluxes were estimated from the diurnal variations in extracellular potassium content corrected for dietary intake and urinary potassium loss. The net fluxes between ICF and ECF were found to be counterbalanced by the circadian rhythm in urinary potassium excretion. Desynchronization of these rhythms would result in marked fluctuations in extracellular potassium content. These findings suggest that some revision is required of the concept of basal state in potassium homeostasis.

Moore Ede, M. C.↗

NASA NTRS1975

Weightlessness

Significance of gravitation forces in regulating homeostasis is discussed, along with weightlessness effects on humans and a state of reduced weight (subgravity), such as on the moon. Biomedical effects of weightlessness adaptation to zero G and readaptation to terrestrial gravitation are described for the nervous system, cardiovascular system, metabolism, and musculoskeletal system. Reactions caused primarly by: (1) changes in the afferent nervous system, (2) lack of hydrostatic blood pressure, (3) lack of weight on the musculoskeletal system, and (4) exposure limits derived from the effects of prolonged weightlessness on humans are reviewed. Protection of humans from adverse effects of weightlessness is considered; Skylab missions are also summarized.

I. D. Pestov↗

NASA NTRS1976

The control of calcium metabolism by parathyroid hormone, calcitonin and vitamin D

Advances in analysis of chemistry and physiology of parathyroid hormone, calcitonin, and Vitamin D are described along with development of techniques in radioassay methods. Emphasis is placed on assessment of normal and abnormal patterns of secretion of these hormones in specific relation to the physiological adaptations of weightlessness and space flight. Related diseases that involve perturbations in normal skeletal and calcium homeostasis are also considered.

Potts, J. T., Jr.↗

NASA NTRS1977

Biochemical responses of the Skylab crewmen: An overview

Continuous metabolic and endocrinic monitoring of Skylab crewmen established significant biochemical changes that varied in magnitude and direction but disappeared shortly after return to earth. These changes indicate adaptation by the body to the combined stresses of weightlessness. Transient changes in fluid and electrolyte metabolisms lead to the conclusion that a homeostasis condition had been achieved. Unstable states persisted in the metabolisms of bone mineral, protein, and carbohydrates.

Leach, C. S.↗

NASA NTRS1977

The capuchin monkey as a flight candidate

The highly evolved nervous system and associated complex behavioral capabilities of the nonhuman primates make them good candidates for certain studies in the space environment since deleterious changes in these more complex aspects of a biological status can only be demonstrated by species which share such highly evolved features with man. Important assets which urge the selection of the capuchin monkey for space experiments include his small size, high intelligence, relative disease resistance, nutritional requirements, and lower volume life support systems. The species is particularly suited for experiments on the nervous system or on process under neural control because of the similarity of capuchin and human blood chemistry profiles and endocrine systems involved in the maintenance of homeostasis and vasomotor tone.

Winget, C. M.↗

NASA NTRS1981

Enzymatic capacities of skeletal muscle - Effects of different types of training

Long-term adaptation mechanisms to maintain homeostasis at increased levels of exertion such as those caused by regular exercise are described. Mitochondrial changes have been found to be a result of endurance exercises, while mitochondrial responses to other types of exercise are small. Further discussion is devoted to long-term changes in glucose transport, hexokinase, phosphofructokinase, pyruvate kinase, and the increased sensitivity of an endurance trained muscle to insulin. Less lactate has been found to be produced by the skeletal muscles at the same work rate after adaptation to endurance exercise training, and the capacity for the flux of the two-carbon acetyl chain through the citric acid cycle increases in skeletal muscles in response to endurance training. Finally, endurance training is noted to result in glycogen sparing and an increase in the capacity to utilize fatty acids.

Booth, F. W.↗

NASA NTRS1982

Chronic central vascular expansion induces hypokalemia in conscious primates

Central vascular expansion maintained for four days in conscious squirrel monkeys reconciles the apparently conflicting short-term fluid and electrolyte responses to water immersion and atrial balloon distension, with those described for prolonged weightlessness during space flight. The monkeys are subjected to an increased lower body positive air pressure (LBPP) of 20 torr which produces a 3 cm water increase in the central venous pressure. Results show a marked increase in the urinary excretion of sodium, potassium, and water during the firxt six hours of LBPP, and the diuresis is maintained throughout the period of LBPP, although the levels of sodium and potassium excretion decline after 24 hours of exposure. Plasma aldosterone transiently drops within the first three hours of LBPP, and then regains normal levels within 24 hours, after which time these levels are maintained despite the continued LBPP stimulus. It is suggested that the normal plasma aldosterone levels observed in the experiments, as well as during space flight, might, epresent a relative hyposecretion in terms of volume homeostasis and a relative hypersecretion with respect to plasma potassium regulation. Thus, kaliuresis and marked natriuresis is confined primarly to the first 24 hours of central volume expansion, a period for which comparable data from space flights are lacking.

Moore-Ede, M. C.↗

NASA NTRS1982

Status of joint US/USSR experiments planned for the Cosmos '83 biosatellite mission

The plans and status of the fourth joint US/USSR biosatellite experiment, scheduled to be conducted in the last half of 1983, are discussed. These experiments will be conducted on board an unmanned Soviet spacecraft and will involve two restrained Rhesus monkeys and 10 pregnant rats, as well as a variety of small plant and radiation biology experiments. Three of the joint studies will use the monkeys for studies of biorhythms, calcium homeostasis, and the cardiovascular system. The fourth experiment will study rodent embryogenesis and neonatal behavior and development following in utero exposure to spaceflight. Specialized sensors and battery powered hardware have been designed, fabricated, and qualified for flight.

Souza, K. A.↗

NASA NTRS1982

Alterations in mitochondria and sarcoplasmic reticulum from heart and skeletal muscle of horizontally casted primates

Horizontally body-casted rhesus monkeys are used as an animal model in order to study the physiological changes known as cardiovascular deconditioning which occur during weightless conditions. No difference was found between the experimental and control animals in heart mitochondrial oxidative phosphorylation which indicates that no apparent changes occurred in the primary energy-producing system of the heart. A marked increase in cytochrome oxidase activity was observed in the casted primate heart mitochondria compared to controls, while a 25% decrease in respiratory substrate-supported calcium uptake was found in casted primate heart mitochondria compared to controls. Sacroplasmic reticulum isolated from the primate hearts revealed marked changes in calcium transport activities. It is concluded that the marked depression in cardiac sarcoplasmic reticulum functions indicates altered calcium homeostasis in the casted-primate heart which could be a factor in cardiovascular deconditioning.

Sordahl, L. A.↗

NASA NTRS1983

The physiological effects of simultaneous exposures to heat and vibration

Determination of the effects of exposure to vibration on the body's ability to handle heat stress, and, if so, identification of the specific vibration parameters (frequency and intensity) for both whole-body (wbv) and segmental-body vibration (sbv) that would have the most detrimental effect on the body's ability to maintain thermal homeostasis were studied. Rectal and skin temperatures, heart rates, localized sweat rates, arm-segment blood perfusion rates, respiration rates, oxygen uptakes, and respiratory exchange ratios were measured in six men (22 to 33 yr) during simultaneous exposures to heat and vibration - either wbv or sbv, and during a heated 50 min recovery period. The heat conditions were T (sub db) = 43.5 + or - 0.5 C (mean + or S.E.M.), and RH = 20 + or - 4%. All vibration exposures were divided into two exposure conditions - identical frequencies but at a high intensity (HI) and a low intensity (LI) level. The HI wbv exposure was for 25 min/day at 5 Hz, 0.37 g-rms; 10 Hz, 0.46 g-rms; 16 Hz, 0.72 g-rms; 30 Hz, 1.40 g-rms; 80 Hz, 3.70 g-rms. The LI wbv exposure was for 2.5 hr/day at the same frequencies but at the following accelerations: 0.14 g-rms; 0.18 g-rms; 0.28 g-rms; 0.55 g-rms; 1.44 g-rms. During the sbv the subject stood and grasped a vibrating, in the Z-axis, hand grip with both hands.

Spaul, W. A.↗

NASA NTRS1983

The Plasma Membrane Calcium Pump

Three aspect of cellular calcium metabolism in animal cells was discussed including the importance of the plasma membrane in calcium homeostasis, experiments dealing with the actual mechanism of the calcium pump, and the function of the pump in relationship to the mitochondria and to the function of calmodulin in the intact cell.

Rasmussen, H.↗