The Injury Of Ultrastructure Of Liver Cells And Expression Of GRP78 In Rat Liver Tissue After Different Repeated And Sustained+Gz Exposure

Objective 1. To have the animal model of repeated and sustained positive acceleration (+Gz) on rat liver tissue injury and explore the mechanisms and changes of plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels; 2.To investigate the impact of ultrastructure of rat liver cells after different repeat and sustained+Gz exposure and observe the damage of liver cells 3. To study changes of the distribution and expression of glucose-regulated protein 78 (Glucose regulated protein78, GRP78/Bip) in the liver tissue under the positive acceleration (+Gz) exposure.4. Study and discuss the pathological changes of histological and subcellular structure changes and self-protection mechanism after different repeated and sustained +Gz exposure and provide basic materials for the aerospace medical research.Methods All of twenty four male Wistar rats were grouped randomly into control, +6Gz, +9Gz and +12Gz groups. The test was held in PLA of studying of acceleration. All tested rats were subjected of acceleration rate of 0.5G/s with the peak +10Gz and each+Gz exposure repeated 5 times with an interval of 30min by computed control. The rats were in prone position, which fixed to the centrifuge arm and the direction of rat headed to the axis. Control group rats,however, were not subjected the acceleration stress, only fixed to the centrifuge arm. Plasma of AST and ALT was monitored. HE staining was used to observe morphological changes in liver tissu.Ultrastructural changes of liver cells of rats were observed by transmission electron microscopy. Liver tissue was removed to use for immunohistochemistry and western blot analysis in the expression of GRP78/Bip after different conditions.Results The results revealed that +Gz acceleration stress injury increased serum AST and ALT levels in Table. Compared with the stress control,+9Gz group and +12Gz group significantly increased in plasma ALT and AST compared with control group(*P<0.05). And+12Gz stress has the highest levels in these groups. The levels of ALT in +12Gz group was higher than that in +6Gz group(AP<0.05). HE staining showed, derangement of liver cells, irregular shape, the cell gap is not clear, vacuolar changes in +Gz groups, and with the increase of G value increased. Cell nuclei, cytoplasm, mitochondria and endoplasmic reticulum were complete structure and clear in the control group. Compared with the control group,+6 Gz group microstructure of liver cells was mild damage, showing only mild nuclear swelling, mild stained cytoplasm, and nuclear shrinkage. It was no abnormal nucleolus, mitochondria and endoplasmic reticulum structure;Moderate damage of liver cells in +9 Gz group was appeared. There were the cell membrane defect of the overall structure, hepatocyte nuclear enlargement, nuclear chromatin aggregating to form lumps, chromatin margination, nuclear shrinkage, and a small amount of apoptotic bodies; mitochondrial was swelled and Its cristae was subjected to derange. Though the gap was increasing, the structure was not found to be broken; endoplasmic reticulum was mild expansion; Hepatocyte ultrastructure in +12 Gz group was severely injury. There were severely swelling liver nuclei, nucleoli small and little lumps coming together to form chromatin. Chromatin margination increasing, nuclear shrinkage, and the formation of large apoptotic bodies can be found; Matrix of cytoplasmic staining was deepened, mitochondria, endoplasmic reticulum, and lysosomes dispersed disorderly in cells; There were mitochondrial swelling, mitochondrial membrane rupture, and mitochondrial matrix electron density decreasing. Cristae of mitochondria was reduced, disappeared, and tended to disintegrate or autolyze; endoplasmic reticulum was seriously injured and accompanied with releasing or disappearing. And floe of moderate electron density was appeared. The small tube of endoplasmic reticulum was cracked into large vesicles and expanding foam.Compared with the control group, the expression of GRP78/Bip was observed, which focused mainly distribution in the cytoplasm; the expression of GRP78 in the experimental group is higher than that in the control group (P<0.05).And +12 Gz group was significantly higher than +6 Gz group and the control group (P<0.05). The expression levels of GRP78/Bip in liver tissue increased with the increasing of G value levels; the expression levels of GRP78/Bip in +12 Gz and +9 Gz groups were higher than that in +6 Gz and control group (P<0.05). Conclusion Experimental study of phase I research has found that repeated low positive acceleration (below +6Gz) had no significant effect on liver cells.The ultrastructure damage of rat liver cells were seriously caused after high+Gz (above +6Gz) exposure. Subcellular changes is known from the significantly damaged liver cells.The main mechanism may involve mechanical inertia force, organizing squeeze, oxidative stress and ischemia-reperfusion. At the same time,we found that the liver also started self-protection mechanism. There may be a positive relative expression of GRP78/Bip, which was associated with exposure of increasing G values. More attention was paied to the protection of the liver in pilots after ultra-high Gz flight environment.