大腸ポリープの増殖と隆起

Autoradiographic Studies on Polypogenesis of Large Bowel

　消化管ポリープ，特に結腸，直腸のポリープは癌化の可能性が高いということで重要視されているが，ポリープの増殖に関しては不明の点が多い．私どもはすでに本誌において，「大腸腫瘍の発生に関する研究」と題して，ラットの発癌実験から，①ポリープのprecursorである「異型上皮巣」を発見したこと，②癌のなかには前癌性病変（ポリープ）を経ることなく，de novoに発生するものが多数あるという2点について発表した．今回はこの異型上皮巣のオートラジオグラフから，細胞増殖と隆起の関係を検討したので追加発表する．

　正常の大腸上皮細胞は腺窩の深部で分裂増殖するが，やがて機能的に分化しながら腺窩壁に沿って表層に移行し，最後には被蓋上皮から腸管内腔に脱落する．換言すれば，正常大腸では腺窩深部に増殖層があるとされている．1963年Coleらによると，増殖層が腺窩の表層にtranspositionすることが隆起する際の最初の機転だとされているが，私どもの研究では初期変化は，本来の増殖層である腺窩深部で開始すると考えられた．

　In our previous report about the exerimentally produced tumors of rats colon, we described that hyperplastic polyp arose from “hyperplastic epithelium focus”, adenomatous polyp from “adenomatous epithelium focus” and cancer arose also de novo. In this report, the histogenesis and morphogenesis of colonic polyp were studied with the ³H-thymidine micro-autoradiography about these 3 types of “atypical epithelium foci”. Compared with the macroscopic tumors, the glandular structures of atypical epithelium foci were simple, and it was possible to determine the germinal zone and the proliferative rate of the mucosal cells.

　The germinal zone of normal epithelium was the lower half of the crypt of Lieberkuhn and its labeling index was 29.1％. In hyperplastic epithelium focus, the zone elongated upward as far as the two thirds of the crypt, but the index was similar (29.0％) to that of normal crypt. On the other hand, adenomatous epithelium focus with atypical cells had not only the upward elongation of the zone, but also the elevation (34.8％) of the labeling index in the lower half of the crypt. And the larger the adenomatous lesions became, the more upward the zone elongated. The germinal zone of the macroscopic tumors such as polyp or cancer could not be decided accurately, but in benign polyp the covering epithelium had no capability to proliferate. In cancerous lesions the distribution of the labeled cells was not uniform and the index was 26.1％.

　These autoradiographic findings of atypical epithelium foci showed two conclusions. First, the initial change of the polypogenesis appeared at the lower portion of the crypt. Secondly, it was reasonable to make a distinction between adenomatous polyp and hyperplastic polyp for the reason of the different genesis of each lesion.