An experimental study of the effect of infusion drugs on the structure of the The balance of temperature in humans and animals is considered as one of the most stable homeostatic constants and is vital to maintain the metabolic processes, function of the cell membranes and tissues and ensures the functioning of the circulatory system on the whole. Therefore, the aim of our study was to establish the structural organization of muscle fibers, neuromuscular nerve junctions and their vascular bed within a norm and changes caused by experimental general deep hypothermia. A total of 85 adult white laboratory male rats, which were divided into experimental, control and intact group, were enrolled in experiment. Experimental, histological, electron microscopy, biochemical, morphometric and statistical methods were used in this investigation. Various types of muscle fibers were differentiated in the study: with high, intermediate and low activity of Succinate Dehydrogenase. Muscle fibers with low activity of Succinate Dehydrogenase have the largest diameter ((60.01±1.81) mcm) and constitute 2.59 % of all fibers. The most numerous are muscle fibers with intermediate activity of Succinate Dehydrogenase, which constitute – 70.1 % and their diameter is slightly smaller than the previous ones and is (42.81±0.92) mcm. Muscle fibers with high activity of Succinate Dehydrogenase occupy an intermediate position both in number (27.31 %) and are the smallest in size ((35.65±1.33) mcm). There are three types of muscle fibers according to ultramicroscopic investigation based on to the volume of mitochondria and content of glycogen. The neuromuscular endings formed by neuromuscular junctions are characterisized by the following data: a total area (6.64±0.34) mcm2, the length of synaptic contact – (1.81±0.34) mcm, the number of folds of the postsynaptic membrane 9.11±1.23, the distance between folds – (0.35±0.15) mcm, the length of a single fold – (2.79±0.54) mcm, the number of synaptic vesicles – 161.23±13.65. On the 3-7th day after exposure to general deep hypothermia there was a narrowing of the delivered and expansion of the capacitive link of the microcirculatory tract. At the same time, the number of capillaries per muscle fiber has decreases by 24.8 %, and in the area of the neuromuscular junction this figure lessens by 22.2 % (in all cases p <0.05). Moreover, there were destructive-edematous changes observed in the walls of the micro-vessels with increased permeability and the formation of sub-endothelial swelling. Moreover, the histological examination show that there was a loss of transverse striation and edematous changes in muscle fibers, which lead to the increase in their diameter. The number of muscle fibers with intermediate (by 3.8-7.6 %) and low (by 144.8-203.4 %) Succinate Dehydrogenase activity increases with a simultaneous decrease of muscle fibers with high Succinate Dehydrogenase activity (by 20.9-30. 3 %). The area of neuromuscular junction has declined by 39,8-36.3 % due to distraction, the length of the junction decreased by 22.4-40.0 %, the number of folds of the postsynaptic membrane dropped by 29.5-45.8 % with the increasing distance between them in 1.4-2 times, the number of synaptic vesicles has reduced by 34.58-43% (in all cases p <0.01). There was a partial restoration of the blood supply to the masseter observed on the 14-30th day after hypothermia which was confirmed by a dilation of arterial vessels and narrowing of the venous microcirculatory tract. There was a growth in number of capillaries per one muscle fiber by 26-40 %, whereas they increased at neuromuscular junction by 47.5-49.0 % comparing to the statistic gained on the 7th day (in all cases p <0.05). Furthermore, the tendency of micro circular restoration appear noticeable as well as a decrease of the diameter in muscle fibers. There was also a marked renewal of histological structure in the muscle fibers and their macronutrient composition. Thus, there are three stages observed in the masticatory muscle under influence of deep general hypothermia: reactive-destructive processes (third day); severe destructive changes (7th day); compensatory-restorative processes (14-30th day). Key words: masseter muscle, blood vessels, muscle fibers, neuromuscular junctions, general deep hypothermia. Branch-Medicine.
