Erythropoiesis in the X-irradiated, bled rat.

Exposure to low levels of x-irradiation (50R) followed by phlebotomy (50% blood volume) one month post-irradiation, resulted in identifiable alterations of the erythropoietic status of the rat. The red cell indices revealed a decrease in mean corpuscular volume and an increase in mean corpuscular hemoglobin concentration. The half-life of 51Cr-labeled erythrocytes was 16.7 days versus 14.4 days for the untreated controls. These subjects also demonstrated hyperplastic marrows with an approximate 60% mean increase in marrow cellularity. A reproducible mortality of 25% was seen at 17 weeks post-irradiation; the one group of animals followed for an extended period exhibited an 86% cumulative mortality at 23 weeks. The observations supported the concept that x-irradiated rats exposed to a relatively low dose of X-rays (less than 10% LD/50) maintain a latent or residual injury of the bone marrow. These animals, when subsequently challenged by phlebotomy, are placed at greater risk with respect to their ability to survive.