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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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The effect of thyrocalcitonin (TCT) injections on the metabolism of water and electrolytes in free-moving and immobilized chinchilla hares is described. Calcium excretion from immobilized animals was elevated, but normalized in those also receiving TCT injections. TCT also normalized water content and excretion rates.
A 30 day hypokinesia in rabbits led to a considerable lag in weight gain for the skeletal bones, reduction in Ca45 uptake, and an increase in isotope resorption rate in the rapidly metabolized fraction of extremity bones. On the other hand, Ca45 content in the teeth and maxillae increased, which may be explained by redistribution of isotope among the various mineralized tissues. Injection of thyrocalcitonin (50 IU/day) produced a distinct normalizing effect on Ca45 uptake and resorption in the mineralized tissues of rabbits kept hypokinetic.
Physical immobilization, inaction due to space travel, a sedentary occupation, or bed confinement due to a chronic illness elicit similar alternations in the metabolism of man and animals (rat, rabbit, dog, mouse). After a preliminary period of weight loss, there is eventually weight gain due to increased lipid storage. Protein catabolism is enhanced and anabolism depressed, with elevated urinary excretion of amino acids, creatine, and ammonia. Glycogen stores are depleted and glyconeogenesis is accelerated. Polyuria develops with subsequent redistribution of body fluids in which the blood volume of the systemic circulation is decreased and that of pulmonary circulation increased. This results in depressed production of vasopressin by the posterior pituitary which further enhances urinary water and salt loss.
The oxygen uptake and tissue gas homeostasis of restrained albinic rats remained relatively constant during a 60 day experiment. The gas metabolism in some tissues changed, and O2 consumption increased in the liver and decreased in the myocardium. Capacity for physical work was reduced by five times. Hypokinesia for 60 days resulted in a delay in the animals growth.
Glycolysis and the intensity of protein synthesis were studied in 140 white male rats in subcellular fractions of the myocardium during 45 day hypodynamia and hyperbaric oxygenation. Hypodynamia increased: (1) the amount of lactic acids; (2) the amount of pyruvic acid; (3) the lactate/pyruvate coefficient; and (4) the activities of aldolase and lactate dehydrogenase. Hyperbaric oxygenation was found to have a favorable metabolic effect on the animals with hypodynamia.
A metabolic balance study was conducted on the three crewmembers of the 84-day Skylab IV earth orbital mission. Dietary intake was controlled, monitored, and kept very nearly constant for a period commencing 21 days prior to flight, throughout flight, and for a period of 18 days postflight. Within the first 30 days of flight urine calcium rose to a level approx. 100% above preflight levels and remained elevated for the remainder of the flight. Fecal calcium excretion increased more slowly but continued to accelerate throughout the flight and did not return to baseline levels during the postflight period. Urinary nitrogen increased to 25-30% above preflight levels within one month following launch and thereafter gradually subsided toward control values. The overall losses of calcium averaged approx. 200 mg per day throughout the mission while nitrogen losses averaged 590 mg. Various other indices of musculoskeletal deterioration are discussed and correlated. The parallelism between the effects of weightlessness and bed rest is reviewed. It is noted, that no evidence is yet available as to the identity of the initial biological response to the absence of gravity.
By using hardware and software originally developed for manned spacecraft, metabolism is now measured while subject wears a loose-fitting mask. This more comfortable, less-restrictive measurement technique uses speed, accuracy and control capabilities of a microcomputer. Because mask imposes minimum interference to subject undergoing testing, it can be used to measure respiratory responses to such activities as treadmill exercise. Mask can be worn for long periods with little discomfort.
The administration of saccharose (3 g per 1 kg for 2 months) intensified changes encountered in hypokinesia. There was a more marked increase in the content of cholesterol, pre-beta and beta-lipoproteins, phospholipids, and glycosaminoglycans in the blood. At the same time, the administration of saccharose improved the course of metabolic processes in the liver of immobilized rabbits, restored to normal levels the reduced glycogen level, the rate of glycolysis and the conversion of cholesterol to bile acids and their discharge in the cystic bile.
Results of this study on mice provide the first direct evidence of insulin resistance for glucose metabolism in skeletal muscle that has undergone a previous period of reduced muscle usage. This lack of responsiveness to insulin developed in one day and in the presence of hypoinsulinemia. Future studies will utilize the model of hindlimb immobilization to determine the causes of these changes.
Results of measurements of food uptake and body weight changes occurring in rats suspended from a harness so that the antigravity muscles were not used for locomotion are presented. The rats were tested in pairs, with both in a harness but only one suspended off its hind legs; this section lasted 7 days. A second phase of the experiment involved feeding the nonsuspended rat the same amount of food the experimental rat had consumed the previous day. All rats experienced decreased in body weight and food intake in the first stage, while in the second stage the suspended rat lost more weight. The total oxygen uptake, CO2 output, and rate of C-14O2 production were depressed in the suspended rats, then returned to normal levels once the rats were back on the ground. It is concluded that the gross metabolic processes are unaffected by simulated weightlessness.
Several experiments concerned with the exposure of animals to acute or chronic centrifugation are described. The effects of hypergravity particularly discussed include the decreased growth rate and body weight, increased metabolic rate, skeletal deformation, and loss of body fat.
An experiment to determine how the longevity of individual animals and genotypes within species depended on body weight and metabolic rate is described.
Amino acid metabolism in hypokinesia is discussed. The effects of passive stretching of muscles in hypokinesia are considered.
The notion that injury to mitochondrial DNA is a cause of intrinsic aging was tested by correlating the different respiration rates of several wild strains of Drosophila melanogaster with the life-spans. Respiration rate and aging in a mutant of D. melanogaster deficient in postreplication repair were also investigated. In agreement with the rate of living theory, there was an inverse relation between oxygen consumption and median life-span in flies having normal DNA repair. The mutant showed an abnormally low life-span as compared to the controls and also exhibited significant deficiency in mating fitness and a depressed metabolic rate. Therefore, the short life-span of the mutant may be due to the congenital condition rather than to accelerated aging.
Metabolic changes on hypokinetic rats were measured. Two groups of animals were studied: (1) weight bearing control which were tail casted but allowed to walk on all four limbs, and (2) hypokinetic with no load bearing of the hindlimbs. The control and hypokinetic rats gained weight at a steady and similar rate over 6 days. Hypokinesia for 6 days led to significantly lower relative weights of the soleus, gastrocnemius and plantaris muscles. Hypokinesia did not effect the relative mass of the anterior tibialis or extensor digitorum longus (EDL) muscles.
Animal hypergravitational effects on metabolism and thermoregulation was studied. The two major problem areas investigated are: initial and short-term exposure effects, and chronic, long-term exposure effects involving developmental and adaptational effects. Investigations focused on: (1) quantifying changes in thermoregulation with graded G-intensities in rats; (2) further delineating the effects of duration on gluconeogenesis, gluconeogenic hormones and substrates, and glucose homeostasis; and (3) reproduction and neonatal survival rates under different G-intensities.
The effects of sex steroids on muscle weight and oxidative capacity of rat planaris muscles subjected to functional overload by removal of synergistic muscles were investigated. Ten weeks after bilateral synergist removal, plantaris muscles were significantly hypertrophic compared with unoperated controls. After this period, the ability of the muscles to oxide three substrates of oxidative metabolism was assessed. Experimental procedures are discussed and results are presented herein. Results suggest a lack of beneficial effect of sex hormone status on the process of hypertrophy and on biochemical changes in overloaded muscle. Such findings are not consistent with the idea of synergistic effects of sex steroids and muscle usage.
The systemic and renal acid-base response of monkeys during ten weeks of immobilization was studied. By three weeks of immobilization, arterial pH and bicarbonate concentrations were elevated (chronic metabolic alkalosis). Net urinary acid excretion increased in immobilized animals. Urinary bicarbonate excretion decreased during the first three weeks of immobilization, and then returned to control levels. Sustained increases in urinary ammonium excretion were seen throughout the time duration of immobilization. Neither potassium depletion nor hypokalemia was observed. Most parameters returned promptly to the normal range during the first week of recovery. Factors tentatively associated with changes in acid-base status of monkeys include contraction of extracellular fluid volume, retention of bicarbonate, increased acid excretion, and possible participation of extrarenal buffers.