1.B細胞とインスリンに関する光線顕微鏡レベルでの問題点
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概要
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The problem as to what is stained by the beta granule stainings seems to be one of the most important problems to be elucidated in the field of pancreatic islet at the level of light microscopy. The two main stainings, aldehyde fuchsin (AF) and pseudoisocyanin (PIC) were thus analysed with special reference to the relation of stained substance to insulin.<BR>First experiment. Adult guinea pigs (unfed for 24 hrs) were given an intraperitoneal injection of glucose (2g/kg) and killed every hour until 6 hrs after that. The histological sections of the pancreas revealed that most of AF stained as well as PIC metachromatic granules in the B cells which filled the cytoplasm in the control animals disappeared in 2 hrs after glucose administration. A bio-assay of the insulin content of the same pancreases indicated that 50% of insulin had been lost from the pancreas of the 2 hr cases.<BR>Second experiment. Adult rabbits (unfed for 24 hrs) received an intravenous injection of alloxan (200 mg/kg) and were killed at various time lapses, mainly 30 min and 24 hrs after the injection. The B cell granules as stained by AF and PIC did not, until 24 hrs, show any decrease in their amount within the cell and in their stainability, although conspicuous damages of the B cell were recognized already 30 min after alloxan treatment. A bio-assay study on each of the animals revealed a 26% and 40% decrease in insulin content of the pancreas in the 30 min and 24 hr cases respectively. As some islets were found to survive under the effect of alloxan, it is supposed that the insulin in the alloxanized pancreas may be gathered in those islets; the insulin content in the damaged islets may thus be lower than indicated by the above figures. This suggestion is supported by that the zinc content (dithizon staining) of the damaged islet, especially in 24 hr cases, is extremly low whereas it is at a considerable level in the surviving islets.<BR>The first experiment of glucose administration indicates that the distribution of the substance demonstrated by AF and PIC well reflect the dynamics of insulin whereas the second with alloxan treatment shows that the amount of the stained element may by far deviate from that of insulin within the cell.<BR>What is then the substance shown by these so to called insulin stainings? It moves and is released together with insulin in the normally functioning B cell as shown in the case of glucose administration. It is, however, left in the cell when insulin is lost from it by an acute cell damage as in the case of alloxan intoxication. A reference to the electron microscopic findings suggests that an element fulfilling this condition may be the membrane sac of the beta granules. The fact that the AF positive and PIC metachromatic substance is not recognized in the pancreas fixed either in ethanol or in aceton may suggest that it would contain lipid.<BR>Although PIC is generally believed to be a special dye causing metachromatic reaction of B cell granules, the present study revealed that more routine basic dyes such as toluidin blue cause a weak metachromasia which is conspicuously intensified when the sections are previously oxidized with KMnO<SUB>4</SUB>.<BR>In the present communication, a consideration was also made on the above mentioned early decrease in the insulin content of the pancreas in alloxan treatment. The blood glucose level (by glucose oxidase method) showed a sharp drop two to five min after the injection. This initial hypoglycemea which continues only one min well corresponds to that of the early decrease in the insulin content of the alloxanized pancreas and suggests that a considerable amount of insulin may be released as early as a few minutes after the alloxan administration.
- 日本内分泌学会の論文