FACTORS INFLUENCING HEMATOPOIETIC SPLEEN COLONY FORMATION IN IRRADIATED MICE

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Abstract
Mice were irradiated repetitively at 6 week intervals. The proliferative capacity of the hematopoietic stem cell compartment was studied after each irradiation and compared to that of age-matched controls which were irradiated only once. Hematopoietic proliferation capacity was measured by determining the number of spleen colonies, splenic Fe uptake, spleen weight, and volume of packed red cells 10 days after irradiation. Six weeks after the 1st irradiation, the hematopoietic compartment was apparently supranormal in size for, when such mice were again irradiated, their postlrradiation hematopoiesls was in excess of that of the controls. Therefore, there was a steady decline in regenerative capacity with each sequential irradiation. After the 6th irradiation, the number of spleen colonies and Fe uptake were reduced to 1/5 of that of singly irradiated controls. The degree of measured decline in hematopoietic proliferative ability was less than that observed by other investigators who studied the effect of serial transplantation of cells upon their ability to proliferate. Furthermore, even after the sixth irradiation, a marked stimulation of post-irradiation hematopolesis was induced by bleeding the animals before irradiation.