THE BULLETIN OF TOKYO MEDICAL AND DENTAL UNIVERSITY

A slicing technique for the preparation of a tooth specimen is described. A low speed saw (ISOMET) was used for this modified technique. It is a slicing machine fitted with a diamondimpregnated cutting disc of 0.5 mm in thickness. The formalin was used for lubrication to serve as both a coolant and a fixative simultaneously. It is thought that the preparation will not damage or disturb the surface of the tooth specimen by careful management under 200 rpm with a loading of 50 grams. The cutting of slices can be controlled by adjusting the specimen arm with a micrometer to the desired thickness. A high quality histological preparation can be obtained when the specimen is sliced as mentioned above soon after it is removed from the living body before decalcification. By the observation of specimens such as the resected jaw bone or other large hard tissue specimens, it is suggested that the sliced specimens of 2 mm in thickness can be obtained routinely for histological study by using this method.

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Carcinoma of the colon was induced in rats by injection of a carcinogen 1,2-dimethylhydrazine (DMH), and thymidylate synthetase (TS) and thymidine kinase (TK) activities, which catalyze the biosynthesis of dTMP by the de novo pathway and the salvage pathway of pyrimidine synthesis, respectively, were measured in normal control colon, DMH-treated normal colon, and DMH induced colon carcinoma with or without administration of two doses of an anti-cancer drug UFT (a combination of tegafur and uracil). TS and TK activities were both increased after treatment with DMH, markedly in colon carcinoma tissue, and to a lesser degree in normal-appearing colon tissue. This phenomenon is well explained by the hypothesis that biochemical alterations of DNA-synthesizing enzyme activities occur as a preliminary step prior to the development of overt cancerous transformation. A low dose of UFT inhibited TS activity but enhanced TK activity, therefore, the salvage pathway may compensate for the reduced level of the de novo synthesis. On the other hand, a large dose of UFT reduced both TS and TK activities, perhaps due to cytotoxic effects of UFT incorporation into RNA.

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