334 D. SLADIC-SIMIC, N. ZIVKOVIC, D. PAVIC, AND P. N. MARTINOVITCH 



DISCUSSION 



trPTON: Were these the first and second generation or the first and second litters? This was 

 something I wasn't quite sure about. 



MARTINOVITCH: The first and the second generation — the first litter of the first filial and 

 the first Utter of the second filial. 



eussell: Did you get the increased litter size in the second fihal? 



MARTmoviTCH: The litter size in the second fihal generation was the same as in the control 

 animals. 



eussell: By irradiating adult mice some time ago Mrs . Russell got an increase in their Utter 

 size with certain doses, certainly an increased ovulation — a super- ovulation effect from 

 irradiation — in the first Utter following irradiation, if the radiation was timed at the right 

 interval before this particular ovulation. Tliis was for higher doses, with some effect at 

 the lower doses too. I wasn't quite sure of the data on the damage, deaths after birth and 

 so on, but we haven't seen anything like this in mice of the filial generation. There is also 

 an increase in the death of embryos, which does not offset the total effect. There are more 

 eggs ovulated. Some of these are killed in embryo so that there is an excess death of 

 embryos as compared with controls, but the net effect on Utter-size is still an increase. This 

 death is aU in embryos at the time of implantation — we've not seen any significant 

 increase in the effect after this time, even with fairly high doses. 



MARTINOVITCH: A difference was found in the sensitivity of the ovaries in respect of the 

 onset of steriUty m rats of different ages, and a difference in the effect on the germ ceUs is 

 also supposed. The progeny of female rats irradiated when 8-days-old was the only one 

 foUowed, as no progeny from irradiated adult rats were available for comparison. 

 UPTON: I have the impression that the female rat was relativel}^ radioresistant as regards 

 the sterilizing of the ovary. I was especially interested in your Table III. I'm not sure I 

 fuUy understood it but there seems to be quite extensive kiUing of early oocytes. 

 MARTINOVITCH: The two processes go hand in hand, dying off of some of the primary 

 oocytes and stimulation of the others. 



UPTON: It would seem that 50 days foUo-nong the dose of 100 r you have only 176 oocytes 

 left, as opposed to 7,300 in the control. Surely tliis would indicate a very high radio- 

 sensitivity of these primary oocytes. 



MARTINOVITCH: Tliis oiily shows the high sensitivity of primary oocytes at tliis particular 

 stage of development. 



mole: I would Uke to emphasize something that RusseU touched on and that is that there 

 is a very large degree of species difference in sensitivity of the ova winch is unlike any 

 other radiobiological response in mammals that I know of, because there is something 

 like a 100-fold difference at least in radiosensitivity. Different laboratory animals (and 

 man) are certainly at least ten times more resistant than the mouse, and possibly 100 

 times more resistant. This is, I tliink, a matter of very great interest as well as possible 

 practical importance. 



