Discussion 57 



some reservations, because these data do not agree with what we know 

 about haemoglobin synthesis in vivo from other studies, for instance 

 those of Prof, de Hevesy. 



Lajtha: In connection with haemoglobin synthesis, we have done 

 some irradiation of bone marrow in vitro and iti vivo. In our in vitro 

 studies we irradiated with doses of up to 5,000 r and then studied the 

 iron uptake with a high resolution autoradiography. We could detect 

 no increase or decrease in the uptake, neither in normoblasts nor in 

 erythrocytes. Jn vivo we gave up to 220 r. Bacq and Nizet gave 800 r 

 in vivo, and they gave huge doses, up to 100,000 r, in vitro. 



Alexander: They gave those large doses in vitro because small doses 

 had no effect; they irradiated reticulocytes outside the dog and they 

 got no decisive effect until they reached 100,000 r. 



Gray: They did get one effect at about 500 r. One gets the impression 

 that with the four dogs the results were rather variable. In one case an 

 effect was obtained at 500 r and in another none was observed at 10,000 r. 



Alexander: I know the details of this work fairly well. The conclusion 

 which is based on limited data only is that plasma from an irradiated 

 dog was sufficient to stimulate unirradiated reticulocytes to greater 

 haemoglobin synthesis. The results about which I think there can be 

 no doubt are that the reticulocytes taken from dogs irradiated with 

 500 r synthesize haemin at a considerably faster rate than those which 

 had not been irradiated. 



Lajtha: How long after irradiation did they take blood from the dog 

 to measure the reticulocyte stimulation? 



Alexander: They took it as soon as they could. 



With regard to the general problem of changes in enzyme activity 

 after irradiation of animals, Prof. Bacq and I reached the conclusion 

 a few years ago on reviewing the literature that there seem to be no 

 immediate decreases and in a few cases there was an increase in activity. 

 The effect of radiation may be to disturb the internal barriers of the cell 

 so as to allow enzymes to get access to sites from which they are normally 

 excluded (Bacq, Z. M., and Alexander, J. (1955). Fundamentals of 

 Radiobiology, p. 187). In this way one would find an increase in activity 

 if one looks immediately after irradiation. But after a time there will 

 be a loss in activity due to the mutual destruction of enzymes which 

 radiation had allowed to come together. An experiment is under way 

 at the moment to test this hypothesis. Errera found that the rigidity of 

 a nucleoprotein gel obtained by placing nuclei in water was decreased 

 by irradiation. The effect was greater when the intact cells were 

 irradiated than when the isolated nucleoprotein was irradiated. With 

 Prof. Bacq we have now done some experiments on spleen nuclei; if one 

 puts spleen nuclei into water they swell very much but do not go into 

 true solution, since on high speed centrifuging all the u.v.-absorbing 

 material (DNA-protein) goes to the bottom of the cell. On standing for 

 as little as 30 minutes at room temperature, but not at 0° C, this is no 

 longer the case and the u.v.-absorbing material is not spun down. It 

 looks as if an enzyme is liberated during the swelling of the nuclei in 

 water, which attacks the nucleoprotein gel and changes it from a gel 



