Lutsenko D. State of microhemocirculatory system and heart rate autonomic regulation of rats under different cold-acclimation regimens.

The research object was the structural and functional state of animal cardiovascular system in the context of adaptation to cold. The research aim was to investigate the state of microhemocirculatory bed and vegetative regulation of heart rhythm in rats in conditions of continuous and rhythmic cold acclimation. Research methods were as follows: modelling of cold acclimation in rats by methods of continuous keeping in cold conditions and rhythmic action of cold exposures; a test of forced swimming in cold water to evaluate the adaptive capacity of the body; electrocardiography followed by heart rate variability analysis; in vivo microscopy of vessels of skin, femur muscle, liver and brain (using fluorescented and polarized light) followed by morphometric analysis of photo and video images; histological analysis of blood to determine leukocyte composition, followed by the calculation of leukocyte indices; determination of the level of nitric oxide end products in tissues by Griess reaction; measuring the osmotic fragility of erythrocytes by the method of small-angle light scattering to calculate the erythrocyte sphericity index; statistical analysis. For the first time, it was shown that the use of continuous and rhythmic regimens of cold acclimation resulted in different responses of the vessels in the brain, skin, muscles, and liver of rats. For the first time it was found that the animals with different baseline levels of autonomic heart regulation after prolonged regimens of cold acclimation implemented some strategies, differing in the degree of involvement of the sympathetic and parasympathetic parts of the autonomic nervous system. For the first time the use of continuous and rhythmic regimens of cold acclimation have been led to the changes in osmotic fragility of rat erythrocytes. It was for the first time shown that after continuous and rhythmic regimens of cold acclimation there was a decrease in the concentration of nitric oxide metabolites in serum. The continuous cold acclimation led to an increase in the level of nitric oxide metabolites in and rhythmic cold acclimation did to a decrease in their level in the cerebral cortex tissues.