Effects of Hypothermia and Self-Warming on Activity of Ca(2+)-Dependent Neutral Proteases in Tissues of Ground Squirrels and Rats.

Effects of hypothermia and subsequent self-warming on activity of Ca(2+)-dependent neutral proteases were studied in tissues of ground squirrels and rats. Moderate hypothermia did not significantly change activity of Ca(2+)-dependent neutral proteases in the analyzed tissues of ground squirrels, but reduced protease activity in rat heart. Severe hypothermia reduced enzyme activity in the analyzed tissues of rats and ground squirrels.

Activity of Ca2+-dependent neutral proteases in tissues of ground squirrel during hibernation and during self-warming after induced awakening.

Cyclic changes in activity of Ca2+-dependent neutral protease occur during preparation for hibernation, with an increase in September and November and decrease in October and December. During hibernation proteolytic enzyme activity decreased, while during self-warming after induced awakening, the role of Ca2+-dependent processes in the tissues of ground squirrels increased according to the body temperature.

Changes in activity of neutral proteases in tissues of ground squirrels in the dynamics of hibernation.

Total activities of neutral proteases in the cerebral, hepatic, and myocardial tissues of ground squirrel vary during hibernation: in autumn (before hibernation) activities of the enzymes in the brain and myocardium start increasing, while in the liver they do not change. A common feature for all tissues is minimum activity of active neutral proteases in the middle of hibernation month 1 bout, while the maximum activity is recorded before awakening.

Oxidative modification of plasma proteins during hypothermia and after dalargin administration.

Short-term and prolonged (3 h) moderate (30 degrees C) hypothermia intensified oxidative modification of plasma proteins, while deep hypothermia (20 degrees C) decreased the intensity of this process to a control level. Preliminary intraperitoneal injection of dalargin had practically no effect on oxidative modification of plasma proteins during moderate hypothermia.

[Activity of liver and brain arginase during hypothermia].

The content of urea and activity of arginase in the brain and liver have been determined in squirrels falling into hibernation and in rats with an artificial decrease of the body temperature. It is shown that the intensity of urea synthesis under hypothermia (20, 10 degrees C) in the studied organs of animals falling into hibernation remains at high level in contrast to animals without such adaptation.

[Acetylcholinesterase activity in brain slices of rats subjected to cooling].

The acetylcholinesterase (AChE) activity is studied in rat slices of the cerebral cortex, corpus striatum, hypothalamus and medulla oblongata of rats during hypothermia (20 degrees C) and also 1 and 7 days after the posthypothermal period. Cooling of animals down to 20 degrees C is accompanied by an increase in the AChE activity in the brain both under incubation temperature of 20 degrees and 37 degrees C. Under prolonged hypothermia the AChE activity in the investigated brain regions, except for corpus striatum, returns to the control level.

[Homocarnosine levels in repeated hypothermia and hibernation].

Compulsory cooling of rats (20 degrees) and susliks (20 degrees-10 degrees) leads to a considerable decrease of homocarnosine in cerebral hemispheres in midbrain and diencephalon and cerebellum. When hypothermia is repeated 4 or 7 times (in every 24 h) a more considerable decrease in the homocarnosine quantity in the rat brain takes place and it is not normalized after self-warming of the organism. After 11-12-fold hypothermia, when a certain adaptation of animals to cooling is developed, the second increase of homocarnosine content with subsequent normalization of its level in great cerebral hemispheres and in cerebellum at self-warming is observed.

[ATPase and acetylcholinesterase activity of the brain in hypothermia].

Short-term hypothermia, caused by cooling of rats down to 20 degrees, decreased distinctly the Na+, K+-ATPase activity in brain homogenates incubated at 37 degrees and did not affect the enzyme activity in the homogenates incubated at 20 degrees. The longer hypothermia (2 hrs at 20 degrees) did not affect the Na+, K+-ATPase activity at 37 degrees (during incubation) and decreased the enzymatic activity in homogenates of middle brain and diencephalon at 20 degrees during the incubation. Contrary to Na+, K+-ATPase, the activity of acetylcholinesterase was markedly increased in brain tissues of rats with hypothermia (irrespective of the temperature of incubation) as compared with control animals.

[Aminotransferase activity in the brain of rats of various ages during hypothermia].

Studies have been made on the activity of aspartate and alanine aminotransferase in the brain of 1, 4, 12-14, 16, 22 days, 1, 1 1/2, 3 months and 2 years old rats under hypothermic conditions (20-19 degrees C). It was shown that hypothermia decreases both total and specific activities of the enzymes in the developing brain. Alanine aminotransferase activity in brain homogenates determined at 37 and 20-19 degrees C, exhibits more significant changes than of aspartate aminotransferase.

[Effect of hypothermia on subcellular distribution and various physico-chemical properties of cathepsin D in rat brain].

The total cooling ef rats down to the rectal temperature 30 degrees and 20 degrees C does not change significantly the ratio of the relative specific activity of cathepsin D in subcellular fractions of the rat brain. The gel chromatographic analysis of heterogeneity of cathepsin D molecular forms in subcellular fractions established the presence of a high-molecular (in the fractions of lysosome and microsome mitochondria) and a low-molecular (in the fractions of lysosome and cytosol mitochondria) enzyme forms. Under hypothermia (20 degrees C) in the brain cytosol fraction there arises a minor zone of the cathepsin D activity corresponding to the high-molecular enzyme form.

[Glutaminase activity of the brain during metabolic heating after hypothermia].

It is found that changes induced by moderate hypothermia (30 degrees C) in the brain tissue glutaminase activity and its temperature dependence are not removed after self-heating up to the body temperature of 37 degrees C. Self-heating after deep hypothermia (20 degrees C) causes a considerable increase in the brain tissues glutaminase activity at all studied incubation temperatures (37, 30, 20 and 10 degrees C) as compared to control rats and rats under hypothermia. The increase in the brain tissue glutaminase activity during self-heating of cooled animals may be considered as a compensatory reaction under conditions of a higher utilization of glutamate by the brain.

[Effect of hypothermia on glutamate dehydrogenase activity of the brain].

Glutamate, dehydrogenase activity and its temperature dependence were studied in the rat brain at moderate (30 degrees C) and deep (20 degrees C) hypothermia. Depending on the grade and duration, hypothermia led to an increase in the enzyme activity at all the test temperatures of incubation. It is assumed that an increase in brain glutamate dehydrogenase activity at low body temperatures favours high level of the neurotransmitter glutamate to realize synaptic transmission, which may be regarded as adaptation reaction.

[Temperature dependence of glutaminase activity from the rat brain under hypothermia].

The temperature dependence of the glutaminase activity in rat brain homogenates and at different steps of enzyme purification was studied under normal and hypothermic (20 degrees) conditions. Under normal conditions the enzyme activity shows a complex temperature dependence. Under hypothermic conditions a site with negative temperature dependence appears on the temperature dependence curve.

[Activity and temperature dependence of acid peptidohydrolase in cerebral tissue of adrenalectomized rats under moderate hypothermia].

The activity of acid peptidohydrolase and its temperature dependence were determined in the cerebral cortex and totally in the midbrain and diencephalon of rats in normal state after a false operation and with bilateral adrenalectomy as well as under moderate (30 degrees C) hypothermia of intact, false-operated and adrenalectomized animals. The enzyme activity is established to change more significantly in the cerebral cortex. Adrenalectomy lowers it in the cortex at an incubation temperature of 30 and 20 degrees C.

[Alteration of activities of alanine- and aspartate transaminases in rat brain under conditions of hypothermia of various duration and in adrenalectomy].

Cooling of rats down to the rectal temperature of 20 degrees decreased the alanine- and aspartate transaminase activities in brain tissue. Activity of the enzymes studied was increased after prolongation of the hypothermia within 2 hrs. In adrenalectomized animals hypothermia was responsible for activation of aspartate transaminase and for a decrease in activity of alanine transaminase.

[Free amino acid concentration in the brain during hypothermia and at different times following the hypothermic period].

Content of 19 amino acids was estimated in rat brain hemispheres, cerebellum, midbrain and medulla oblongata both under conditions of hypothermia (20 degrees) and within 1, 3, 7, 15, 45 and 60 days after selfwarming. Hypothermia, depending on its length (5-10, 60 and 120 min), caused various alterations in the pool of amino acids, dissimilar in the brain regions studied. The phasic alterations in the amino acid content were observed in brain tissues during the posthypothermic period.

[Glutaminase and glutamate decarboxylase activity of brain tissue during hypothermia and hibernation].

A forced cooling of rats and gophers decreases the brain glutaminase activity activated with phosphate with the incubation temperature. The cooling of rats leads to a decrease in the brain glutamate decarboxylase activity. However in the animals cooled down to 20 degrees C the incubation temperature (25 and 20 degrees C) does not affect it.

[Content of biogenic amines in brain under artificial and natural cooling of animals].

The catecholamines and serotonin contents in different brain areas were studies in rats under hypothermia of 30 degrees and 20-19 degrees C and in Citellus pigmaeus Pallas on the 7th, 15th and 30th day after hibernation. The artificial and natural drop in the body temperature is shown to increase the catecholamines and serotonin contents in cerebral hemispheres, cerebellum, thalamus, hypothalamus and medulla oblongata. A long artificial cooling is accompanied by a decrease in the value of the catecholamines/serotonin ratio in the brain due to an increase in the serotonin content and a long hibernation by redistribution of the content both of catecholamines and serotonin without changing their ratio.

[Effect of hypothermia on the ammonia-glutamine-glutamic acid system in ground squirrels after hibernation].

The effect of forced cooling was studied as applied to the contents of ammonia, glutamine, glutaminic, asparaginic and alpha-amino butyric acids in the brain of sousliks woken-from hibernation. The cooling of the woken sousliks to the body temperature of 30, 20 and 25 degrees C decreased to some extent the ammonia content in the brain. A deeper hypothermia (10 degrees C) causes its 60,4% decrease as compared to the ammonia amount in woken animals.

[Brain peptide-hydrolase activity in hypothermia].

The cooling of rats to the body temperature of 30 and 25 degrees C does not change acidic peptide-hydrolase activity in tissue homogenates of cerebral cortex, hypothalamus, thalamus, hippocampus, midbrain, cerebellum and medulla oblongata. In deep hypothermia (to 20 degrees C) there occurs a significant increase in the peptide-hydrolase activity in tissue of the studied brain areas both in an incubation sample at 37 degrees C, and at temperature corresponding to the body temperature of cooled animals (20 degrees C). But the enzyme activity remains unchanged in homogenates of medulla oblongata incubation at 37 degrees C.