The action of simulated and true weightlessness on the digestive tract of rats.

Rats on board the Soviet Cosmos 936 satellite for l8 1/2 days showed a decreased glycoprotein secretion from the salivary mucous glands, stomach and intestine, and an increased leucine aminopeptidase and acid phosphatase content from the small intestine. Grimelius positive cells were activated. One group of rats were centrifuged at 1 g during the flight to simulate terrestrial gravity. Some investigations have suggested that under these conditions muscular and cardiac disorders diminished. In the digestive tract the benefits of centrifugation at 1 g are minimal and limited to a few glycoprotein components. The digestive changes are probably the expression of a stress response, unrelated to weightlessness. Similar changes, concomitant with a glycocorticoid hypersecretion, were found in rats after 15 days of hypokinesia on Earth. These digestive changes persisted even in adrenalectomized rats.

Variations in the activTY OF SOME BRAIN AND PLASMA ENZYMES UNDER THE INFLUENCE OF +Gz acceleration.

The present paper refers to the activity of some enzymes associated with the cellular cytomembranes in the plasma and brain of guinea pigs exposed to the action of repeated +10Gz acceleration. Immediately after the last run, diminution of enzymatic activity in the brain supernate ran parralel to a rise in plasma enzymatic activity. Variations in enzymatic activity suggested the liberation of enzymes connected with the neuronal organelles, perhaps consequent to alterations in the permeability or structure of the neuronal cytomembranes. These alterations might also be interpreted as being accompanied by permeabilization of the blood-brain barrier, with release of enzymes from the neuronal structures into the plasma. Changes in the permeability of the neuronal membranes might be attributed to several factors: cerebral hypoxia following the hemodynamic and ventilation alterations induced by hypergravitation, the influence upon the membrane permeability of hormones released in excess under the stress of acceleration, and the strain to which the central nervous system neurones are subjected by the multitude of afferent impulses with a starting point in the various types of receptors stimulated by hypergravitation.

Hypergravitation and sympatho-adrenergic reactivity.

The cardiac frequency and adrenal and urinary catecholamine content were investigated on 10-minutes centrifuged rats (+6 Gz). It was found that the heart responds in an individual manner, with a general tendency to tachycardia. Under the same conditions after 1 1/2 minute the adrenal noradrenaline response was absent, after 3' and 6' the adrenal noradrenaline content was augmented and the adrenaline one diminished, and after 10' the response vanished. Hypergravitation does not change the urinary noradrenaline elimination collected after 10 minutes of centrifugation, but that of adrenaline is augmented in one of the two explored animal groups. The difference between the two groups may be explained by the great individual variations, as results from the cardial frequency (appreciated by teleelectrocardiogram). The environmental stress produces similar but more reduced catecholamine modifications.

Effect of hypergravity and hyperthermia on antidiuretic hormone secretion.

The effect of acceleration and hyperthermia on the antidiuretic hormone secretion (ADH) was investigated in rats both separately and simultaneously. The two conditions of stress elicited a rise in plasma ADH concentration in proportion to their intensity. Concomitant exposure to the two factors produced an additional effect. The parallel histochemical studies using methods for demonstrating RNA, proteins and the neurosecretory material in the supraoptic nucleus, showed the synthesis and depletion of the hormone content in correlation with the plasma concentration of ADH.

Digestive tract of rats after hypokinesia and hypergravitation.

We found in rats submitted to a 7 days interval of hypokinesia a decreased glycoprotein content in salivary mucous glands, gastric and intestinal mucosa, an increased glycoprotein content and an increased content of leucine-aminopeptidase, acid and alkaline phosphatase. Similar changes were found after a short interval of centrifugation (+6 Gz, 10 min). These nonspecific responses were more accentuated if the hypergravitation was performed after 7 days of hypokinesia. We reproduced this way this events that occurred in space flight and deacceleration before landing.

Digestive structural modifications in rats submitted to 15 days of hypokinetical conditions.

Restraining rats for 14 days in special cages in order to determine a hypokinetical state decreased mucopolysaccharide secretion in submaxillary glands and gastric mucosa. In the small intestine and in the colon, concomitantly with an enzymatic (leucine-aminopeptidase and acid phosphatase) hypersecretion as results from specific histochemical reactions. These modifications show maximum intensity at the end of the interval. The corticosterone plasmatic level determined in the same interval also increased, suggesting this way to a causal relation. The histomorphological changes presented delayed reaction. This material is in accord with our previous investigations as well as with some literature data.

The gastrointestinal tract in hypokinetic rats.

In Wistar rats kept for 15, 30 and 60 days in a hypokinetic state in special cages, alteration of some gastrointestinal glands was studied by means of histochemical and electron microscopic methods. After 15-30 days of hypokinesia, a decrease was found in the muco-polysaccharide content of the submaxillary, gastric and duodenal glands. The intestinal goblet cells appeared vacuolated. The oxyntic cells, which secrete HCl, as well as the G antral cells, which secrete gastrin, were in an active state. The hypokinetic rats exhibited increased gastric secretion. The electron microscopic aspect of the principal cells corresponded to augmented pepsin secretion. The enterocytes showed an increase in their leucine aminopeptidase, acid phosphatase and glucose-6-phosphatase content. In the submucosa of the fundus of the stomach an accumulation of eosinophils was observed. These modifications were more striking after 15 than after 30 days, and disappeared after 60 days of hypokinesia. These morphological and functional changes may be explained by glucocorticoid hypersecretion corresponding to a stress reaction.

The digestive tract after 7 days of restraining conditions in normal and adrenalectomized rats.

Hypokinesia produced specific reactions in tissues related to motion (bones, skeletal muscles and myocardium) and nonspecific in others, as that of the digestive tract after 7 days of hypokinesia. A decreased content of glycoproteins from mucous salivary glands, stomach, small intestine and colon, and an increased intestinal content of leucine-aminopeptidase and acid and alkaline phosphatase were found as a result of histochemical reactions. An important plasmatic corticosterone increase was also found. The same histochemical modifications appeared in adrenalectomized rats in which the plasma corticosterone was substantially diminished. Therefore these glycoproteins and enzymatic secretions are not dependent on the glucocorticoid response.

The role of the sympathoadrenergic reaction in adaptation of the organism to the action of + 6 Gz acceleration.

In experiments on rats the symphathoadrenergic reactivity after a + 6 Gz acceleration was investigated. Hypergravitation produced as a rule a short initial bradycardia, followed by tachycardia. Hexamethonium (C6), a peripheric ganglion-blocking agent, produced bradycardia, diminution or vanishing of the initial bradycardic episode, and a decreased tachycardic reaction. No initial bradycardic response was observed ater atropine. Atropinized and C6-treated rats showed an increased heart frequency response. Centrifugation produced a decreased adrenal catecholamine content and a blood noradrenaline elevation. C6 importantly decreased both catecholamines content in blood. On this background the acceleration produced a slight increase of both blood catecholamines.

The effect of +Gz acceleration upon lactate, pyruvate and some nucleotides in the nervous tissue of the guinea pig.

The present paper was designed to the study of the effects of hypoxia induced by positive accelerations upon energy metabolism in the brain. Variations in the amount of lactate, pyruvate, ATP, ADP and AMP were determined immediately after centrifugation and after intervals of 30 to 90 minutes. An increase in the quantity of lactate and pyruvate, and a diminution of ATP running parallel to an increase in AMP were noted immediately after centrifugation. These variations almost entirely disappeared 90 minutes after centrifugation. These findings drew attention to a possible imbalance of the neuronal energy processes, which might bring about, even for short periods, alteration of the neuronal function.

Hypergravitation and sympatho-adrenergic reactivity.

The sympatho-adrenergic reaction of the organism subjected to hypergravitation was investigated in rats exposed to +6 Gz. The electro- and cardiotachograms recorded telemetrically were correlated with the adrenal catecholamine content. The determinations were made in controls and in rats treated with hexamethonium and atropine administered separately or together. The rats reacted to acceleration initially by a short bradycardia followed by tachycardia. In one case there was a sustained bradycardic response. Hexamethonium (C6) lowered the resting heart rate, attenuated the initial bradycardia and reduced the consecutive tachycardia. In some rats during centrifugation a bradycardic and arhythmic response was found sometimes ending in cardiac arrest. Hexamethonium stored the catecholamines in the adrenals as a result of their increased concentration. Atropin brought about resting tachycardia, disappearance of bradycardia from the very beginning of centrifugation and a more accentuated tachycardia. Atropin and hexamethonium administrated together diminished the response to acceleration.

Na+ and K+ dependent ATP-ase and structural modifications in hypokinetic rats.

In rats the hypokinetic state obtained by restraint in special cages, produces after 30 days, a marked decrease in Na+ and K+ dependent ATP-ase in the skeletal muscle. After 15 days hypokinesia the enzymatic content of the investigated tissues did not change. In the left cardiac ventricular muscle Na+ and K+ dependent ATP-ase decreased after 15 days and particularly after 30 days hypokinesia. These changes were brought about by the hypofunctional state of both muscles, which also produced structural alterations. In the skeletal and cardiac muscles electron microscopy revealed fibrillar atrophy and mitochondrial alterations typical of an affected function. In the cardiac muscle, in which these changes were more accentuated, the dissociation of the intercalar disc was also noted, aspects partially described by others.

Circulatory adaptive reactions under hypergravity in normal and cold environments.

Rats subjected to various levels of +Gz acceleration exhibited an increased blood concentration of noradrenalin and adrenalin, indicative of a sympatho-adrenergic reaction. Under the same conditions, from plasma determinations, and by histochemical examination of the supra-optic nucleus, an increased antidiuretic response was noted. This response was reduced in cold environment.

Hydroelectrolytic changes caused by prolonged clinical recumbency.

Investigations effected in 16 subjects of 20-69 years at bed rest after bone fractures demonstrated, in an interval of 10-27 days after surgery, normal plasma sodium concentration and a decreased urinary elimination, an increased plasma potassium concentration but a decreased urinary output. The osmotic changes were not significant. The plasma vasopressin activity was increased. Three urinary aldosterone determinations showed an increased output. The serum calcium level was within normal limits but its urinary output was initially slightly decreased, contrary to its augmented elimination after simple voluntary bed rest, as results from literature. The hydroxyproline elimination was increased, demonstrating an active collagen metabolism.

The influence of magnetic fields on some humoral parameters and on resistance to hyperthermia in rats.

The influence of magnetic fields of moderate intensities (50 and 120 Oe) was studied in rats after single or repeated exposures with or without a rise in environmental temperature. The following parameters were investigated: the number of erythrocytes and leucocytes, the percentage of different varieties of leucocytes, serum Na+ and K+, plasma corticosterone, ascorbic acid in adrenals, blood catecholamines, plasma fibrinolytic activity, plasma antidiuretic hormone. The resistance to hyperthermia was tested after single exposures to magnetic fields and the survival time was measured. The only significant change recorded in the number of blood cells was a leucopenia after single exposures to 50 Oe for 4 hrs. The parameters indicating the activity of the adrenal cortex were not altered significantly. A moderate rise in blood noradrenaline suggested a possible mild stimulation of the adrenergic system. The plasma fibrinolytic activity was significantly stimulated after single exposures, but no change in fibrinolysis could be recorded after repeated exposures to magnetic fields. Changes observed in plasma ADH were not conclusive. The resistance of animals to hyperthermia - as a general test of reactivity - showed minimal changes in the survival time, loss of weight, and rectal temperature in animals exposed to hyperthermia (40 degrees C) under the influence of the magnetic fields.