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.

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.

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.