Structural Changes in Rat Hepatocyte Nucleolus under Nucleolar Stress Caused by Hypothermia.

Structural changes in rat hepatocyte nucleoli were studied during deep hypothermia simulated by immersion in water at 5°C for 40 min (ambient air temperature 7°C). In comparison with the control, phenomena of nucleolar stress occurred in rats during hypothermia: the number of fibrillar centers (FC) per nucleus (by 1.7 times) and per nucleolus (by 1.6 times), nucleolonemal nucleoli per nucleus (by 2.8 times), and the relative content of nucleolonemal nucleoli per nucleus (by 2.6 times) significantly decreased (p=0.0000001); the number of FC per nucleolonemal nucleolus also decreased by 1.4 times (p=0.01). In the hepatocyte nuclei, we observed an increase in the relative content of transitional type nucleoli per nucleus (by 1.3 times; p=0.01), the number of FC per transitional type nucleolus (by 1.4 times; p=0.003), the content of free FC per nucleus (by 3 times; p=0.00004), and the percentage of free FC per nucleus (by 3.5 times; p=0.00004). These changes can be considered as compensatory and adaptive reactions, and transitional type nucleoli can be attributed to the "reserve" nucleolar pool.

Relationship between Cooling Medium and Hepatocyte Ploidometric Parameters in Albino Rats.

Relationship between the method of hypothermic exposure and ploidometric characteristics of hepatocyte nuclei of rats were studied immediately after hypothermic exposure and during the posthypothermic period. The following cooling modes were used: single submersion into 5°C water (until rectal temperature drop to 20-25°C; deep hypothermia) and single exposure at air temperature of -25°C (until rectal temperature drop to 30°C; moderate hypothermia). A manifest destructive effect of deep hypothermia on rat liver was detected: the exposure caused manifest alteration of hepatocytes (alteration index increased 81-fold immediately after the exposure and remained 16-fold higher than normally after 14 days) and an increase of DNA accumulation index with predominance of hepatocytes with 5c-8c nuclei (60% of the population) during the entire period of observation, which indicated intensification of the compensatory and adaptive processes in the liver with predominating high-ploid population of hepatocytes. Hepatocyte alteration processes in response to moderate hypothermia were less intense (hepatocyte alteration index increased 19-fold immediately after the exposure and remained 3-fold higher than normally after 14 days). The DNA accumulation index increased moderately immediately after the exposure and returned to normal after 14 days, with emergence of 2c hepatocytes and an increase in the level of 4c hepatocytes (51% of the population), which indicated realization of a different strategy of liver regeneration - recovery of the cell population intrinsic to intact animals.