Late modifications of cephalic circulation in head x-irradiated rats

A non-invasive and quantitative radioisotope method was applied to the assessment of late cephalic circulatory changes occurring 12 and 21 months after head irradiation at 500, 1000 or 1500 R in rats of two inbred strains. Analysis of the results concerning the tracer circulatory mean transit-time (t) as well as those of two indices measuring respectively the cephalic blood volume (VH) and the cephalic blood flow (FH), led us to conclude that: -- the radiation-induced late changes in cephalic circulation are more relevant to a reduction of the volume of blood flowing in the head than to a reduction of its rate -- even a dose as low as 500 R induces such a late effect but the delay is longer than one year -- a depression of the cardiac output can be an additional very late consequence of head irradiation -- there is an influence of the rat strain on the temporal development of the late cephalic circulatory changes.