978 RADIATION BIOLOGY 



flow is decreased only by a small factor after heavy 13 irradiation of the 

 mouse liver with a Y 90 colloid (20,000 rep in 3 days) (Dobson and Jones, 

 1952). 



The influence of radiation on vascular permeability is largely undeter- 

 mined. From studies of relatively simple systems there is reason to 

 believe that cell permeability is not affected directly unless massive 

 dosages are employed. Although changes suggestive of altered capillary 

 permeability have been described, it is not known whether they are a 

 result of the action of radiation on the endothelium or of alterations in the 

 vascular bed. Intravenously injected dyes appear sooner in patches of 

 irradiated skin. When Evans blue dye is injected into rabbits immedi- 

 ately after local X irradiation, the exposed area turns blue earlier than the 

 nonexposed (Painter et al, 1947). A similar increased localization and 

 concentration of dye has been noted with intravenous trypan blue as 

 long as the injection is made within 1 hour of X irradiation (Rigdon and 

 Curl, 1943). An increased spread of intradermally injected Evans blue, 

 which is presumed to be indicative of an accelerated lymph flow, has also 

 been seen in the irradiated skin of rabbits during the first few hours 

 (Painter et al, 1947); yet, cutaneous lymph flow in man is apparently 

 unchanged following moderate amounts of radiation and may actually 

 decrease with larger dosages (Ane and Burch, 1941). There is little 

 change, moreover, in the output of lymph from the thoracic duct of the 

 cat during the first hours after total-body irradiation (Valentine et al, 

 1948), although an increased lymph flow has been observed in the dog 

 several days later (Bigelow et al., 1951). 



Intravenous Evans blue appears in the irradiated and nonirradiated 

 regions at the same time during the late erythematous reaction of rabbit 

 skin, but this is not the case with fluorescein, which is seen within a few 

 seconds in the exposed area and within several minutes in the nonexposed 

 region (Painter et al., 1947). The reason for this difference is not obvious. 

 It has been suggested that the appearance of Evans blue may be masked 

 by erythema of the irradiated skin. The rapid appearance of fluorescein, 

 on the other hand, may be more a matter of hyperemia than of an increase 

 in permeability of the vascular endothelium. 



Furth and his associates (Furth, Andrews, et al, 1951; Bigelow et al, 

 1951; Wish et al, 1952) have contributed several significant papers that 

 suggest that an important part is played by endothelial damage and 

 increased permeability after total-body irradiation. They have deter- 

 mined that labeled homologous and heterologous plasma, homologous 

 and heterologous erythrocytes, Evans blue, and colloidal radiogold, in 

 general, disappear faster from the circulation of X-rayed than of normal 

 mice and rabbits. Maximum alteration occurs during the second post- 

 exposure week and may be correlated with the period of greatest bleeding. 

 As contrasted with the above observations, a decreased disappearance of 



