Endoreduplication Following Testicular Irradiation

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ENDOREDUPLICATION FOLLOWING TESTICULAR IRRADIATION An increased frequency of chromosomal endoreduplication has been noted (2 1i n peripheral blood lymphocyte cultures following i n vitro") or i n vivo irradiation In tne former situation a precise dose-effect can be achieved. However, if changes in lymphocytic chromosomes are studied following i n vivo irradiation, no such relationship can be developed since it would be impocrible to calculate the precise dose of x-ray administered to the lymphopoietic We have been studying the effects of x-ray irradiation upon human testicular mrphology and physiology. It occurred t o us that w e had an i n vivo model for testing a dose-effect relationship with regard t o endoreduplication in the testis. It is the purpose of this article to report our preliminary observations . Material and Methods Twenty-one normal inmate volunteers a t the Washington State Penitentiary underwent open testicular biopsies. The testicular tissue was cultured for chromosome analysis by the method of Steinberger and Steinberger as described Results from each subject were combined to form the control Three volunteers were exposed to lOOr (95 rads) of x-ray to the testes administered acutely by means of a Maximar 250 KV unit. The specifications include a Thoreus I1 filter and an HVL 2.5 mm copper. Repeat testicular biopsies were performed on two of the inmates four hours after exposure. Three additiorial biopsies were performed on two testicular tissue was treated in subjects 15-42 days post-irradiation. The exactly the same manner as i n the control period.

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The slides of testicular chromosomes were scanned under 44x magnification and a l l prophase and metaphase plates were counted regardless of our ability to karyotype the chromosomes of a n y particular cell. The number and location of all polyploid cells were noted. A photograph of the chromosomes of e a c h of these cells was obtained for more critical evaluation. The polyploid cells were divided into two types : 1) endoreduplicated cells and 2) endomitotic or c-mitotic cells. Endoreduplication was recognized by the presence of diplochromosomes which are paired chromosomes lying i n close apposition (Figure 1) during prophase or metaphase. Endomitotic or c-mitotic cells are also polyploid cells but the chromosomes are not distributed i n pairs A significant increase in endoreduplication (p = <0.01) was noted inthe post-irradiation period a s compared with the pre-irradiation controls (Table 1). T h i s increase was almost exclusively a result of increased numbers of endoreduplicated cells that were cultured on the day of irradiation (p = <O. 01); whereas by 15-42 days post-irradiation, there was no change from control levels (p = >O. 1). Furthermore, at no t i m e after irradiation to the testes was there a significant Endoreduplication occurs asa normal phenomenon i n certain animals and plants. While its presence in the ileum of the larval form of Cules pipiens is occurrence after various manipulative procedures has a different connotation. A n increased frequency of endoreduplication has been reported following the addition of various agents to cells in tissue culture. Since this effect h a s been and its increased cold(') and irradiation(1) it has been thought t o be a

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(1 0)non-specific response of cells t o toxic agents . This may well be the case, although consideration must also be given to the possibility that t h e s e agents tr . may somehow affect some specific mechanism that controls chromosome dupliSchwarzacher and Schnedl(1’) demonstrated that the length of t i m e needed for DNA synthesis i n endoreduplicated cells is approximately double that of diploid cells. Similarly, the amount of DNA per cell has been found t o be roughly twice that of diploid cells(12). Confirmation of the extra synthesis of DNA due to the presence of a tetraploid number of chromosomes has been achieved with tritiated thymidine(13). Since this process occurs during interphase with the chromosomes in the despiralized phase, it cannot be visualized directly by These preliminary studies confirm the findings of a n increased frequency of endoreduplicated chromosomes following in vivo exposure to radiation. studies will be necessary t o establish a dose-response relationship that may be useful a s one component of a biologic dosimeter for radiation exposure.

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10. Editorial, Lancet, 1964, ii, 511. 11. Schwarzacher, H. G., Schnedl, W. Cytogenetics, 1965, 2, 1.