doses at the LD-50 level but also by lower 

 doses, as low as 25 r., and the magnitude of 

 the effect on iron 59 metabolism is related to 

 the radiation dose received. 



The purpose of the experiments was to 

 delineate the changes in the specific activity 

 of iron 59 in the blood, liver, spleen, and kid- 

 ney of the pinfish, after a single radiation dose 

 of 2,000 rads, and to relate these changes to 

 erythrocyte production by correlating them 

 with results previously observed on the cellu- 

 lar blood components of the pinfish after ir- 

 radiation. 



Methods 



Pinfish were collected from the Beaufort 

 estuary and maintained throughout the experi- 

 ment in flowing sea water. Temperature of the 

 sea water varied from 20° to 25° C. and sa- 

 linity from 25 to 32 p.p.t. No attempt was 

 made to separate the sexes, because the fish 

 did not display any external sexual dimor- 

 phism. Test fish were irradiated with a single 

 dose of 2,000 rads of cobalt 60 gamma radi- 

 ation at a rate of 350 rads/min. ^"10 percent. 

 During irradiation the water in which the fish 

 were held was aerated. 



Six groups of five irradiated and five un- 

 irradiated fish were injected intraperitoneally 

 with 0.5 lie. of iron 59 on 1, 8, 15, ZZ, 36, and 

 50 days after irradiation. The high-specific- 

 activity iron 59 (24.4 mc. iron 59/mg. iron) 

 was dissolved in sodium citrate buffer with 

 a pH of 4,2. After the injection of iron 59, the 

 fish were allowed to metabolize the iron for 

 7 days, so that the distributionof iron 59 would 

 stabilize within the fish. Samples of liver, 

 spleen, kidney, and blood were then taken for 

 analysis of radioactive and stable iron. The 

 tissues were dried and weighed, wet-ashed in 

 concentrated HNO3, and diluted to volume with 

 0.25 N HCl. Radioactive iron was measured 

 with a gamma spectronneter attached to a 

 well-type scintillation detector, and total iron 

 content was determined with anatomic absorp- 

 tion spectrophotometer. All results are re- 

 ported in units of specific activity of iron 59 

 (liC. iron 59//ig. iron). 



Size distributions of blood cells after a dose 

 of 2,000 rads were deterrnined on another 

 group of pinfish at 1, 3, 5, 7, 14, 21, and 28 

 days after irradiation. Heparinized whole blood 

 samples were diluted 1 to 25,000 with 1.0 per- 

 cent saline, and cell size distribution patterns 

 were determined on an electronic cell counter 

 and particle size distribution plotter. The re- 

 ported blood cell distribution curves are the 

 mean of five fish. 



Effect of Irradiation on Iron 59 Distribution 

 and Blood Cell Size 



The single radiation dose of 2,000 rads af- 

 fected the distribution of iron 59 in the blood. 



liver, spleen, and kidney of pinfish at different 

 times after irradiation (table 12). Althouth in- 

 dividual variation within each group of fish 

 was considerable, the specific activity of all 

 tissues examined was affected by irradiation. 

 The greatest effect was observed in the blood, 

 spleen, and kidney. To compare the changes in 

 specific activity in the blood and tissues of ir- 

 radiated fish in relation to the specific activity 

 of these tissues in the controls, we converted 

 the data to percentage of control specific 

 activity. 



Table 12. --Specific activity (//c. iron 59//ug. 

 iron X lO"-') tissues of irradiated and 

 unirradiated pinfish 



[ Standard error of the mean in parentheses] 



■'- Refers to number of days after irradia- 

 tion. 



Iron 59 injected into the blood of fish 1 and 

 8 days after irradiation had similar specific 

 activities which were below that of the controls 

 (fig. 30). In fish injected on the 15th through 

 the 22d day after irradiation, the specific 

 activity of the blood decreased, reaching its 

 lowest point on the 22d day after irradiation. 

 The specific activity of the blood increased 

 after the 22d day and was more than twice 

 the level of the controls by the 36th and 50th 

 days. 



The specific activity of iron 59 in kidney, 

 spleen, and liver after irradiation was affected 



55 



