| Research Abstract |
This work was designed to make clear the relationship between the cell renewal rate and the radiosensitivity of the various tissues in the expression of late-radiation tissue damage, especially focused uopon the pancreas. Results of this study indicated as follows; The pancreatic duct cells turned over in a period of 2.7 months in large ducts and 5.6 months in small ducts, suggesting that they constitute a slowly renewing populations. However the pancreatic acinar cells and islet cells indicated expanding cell population and their doubling times were estmated as 7.0 years and 1.3 years respectively. Also preliminary observations indicated the endothelial cells of the pancreas turned over in a period of 3 years, suggesting that they also constitute expanding cell populations. In other parts of tissues of the body, the parenchymal cells of the bile ducts, lung bronchioles, and salivary acini and ducts , and Kupffer cells of the liver also constitute slowly renewing populations. But hepat
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ocytes, renal tubular cells and endothelial cells of kidney and liver comprize expanding populations. In these liver, pancreas, and lung, it was suggested that the duct systems is the target tissues for the late radiation damage as a result of most rapidly renewing characteristics in each organ. However, in respect to the manifestation of the acute radiation cell death, the view point of cell renewal concept was not to applicable to the follwing distinctive cells of the various tissues, that is, pancreatic islet cells, presumptive stem cells of the intestinal epithelia, oocyts, and lymphocytes. From the studies on chemial modification of radiation-induced acute pancreatic islet cell death, the intrinsic factors, that is, their metablism probably related to repair capacities, such as PLDR and SLDR, were suggested to prescribe their mortality. In conclusion, to realize the radiation-induced late tissue damage, it is suggested that the two factors, 1. cell renewal, 2. intrinsic character of the cells should be clarified in each tissue . Less
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