RESUMO
Polyploid cells in the urinary sediments often give an erroneous clinical judgement in cases of post-pelvic irradiation follow-up, but their nature and evolution have remained unclarified. An experimental induction of polyploid cells in the transitional epithelium of the urinary bladder was carried out in Sprague-Dawley rats by administration of 3,000 rads in a single dose, and their sequential morphological changes were analysed under light and electron microscopes. 1. The acute post-irradiation changes of transitional epithelial cells were manifested with two consecutive phases of degenerative process ; the early lesion started to appear from the first day after irradiation and diminished partly at the 7th day; the later changes became enhanced progressively from the 2nd week and maximized at the 3rd week, but regressed thereafter . 2. The general histological alterations of the transitional epithelial cells in the acute stage were characterized by cytoplasmic vacuolization due to profound widening of intercellular cisternal spaces and dilatation of smooth endoplasmic reticulum aside from severe disruption of mitochondria and increase of lysosomes, especially in the superficial and intermediate cells, and by eventual outcome of cell death by nuclear pyknosis and karyorrhexis. 3. The polyploid cell change was demonstrated as a spectrum of the later alterations of acute irradiation injury to the basal layer cells, and appeared early from the 2nd week and regressed after the 4th week. 4. Based on their increased size and nuclear abnormalities, those polyploid cells exhibited features of both amitotic nuclei and cytoplasmic degenerative processes ultrastructurally, and in the acute phase the nuclear indentation and lobulation were associated with increased amount of heterochromatins and margination together with nucleolar enlargement and increase in number. 5. The above cells started to regress thereafter, being terminated by nuclear pyknosis and karyolysis, and numerical reduction of the polyploid cells was accompanied concomitantly with basal (reserve) cell hyperplasia of the remained epithelium. It is of the author's assumption that the polyploid cell phenomenon induced by irradiation onto the transitional epithelium of the urinary bladder is a transient manifestation of irradiated amitotic basal cells during the later phase of acute post-irradiation injury and is subsequently removed out by nuclear pyknosis and karyolytic processes.