Blood responses under chronic low daily dose gamma irradiation: I. Differential preclinical responses of irradiated male dogs in progression to either aplastic anemia or myeloproliferative disease

Male beagles chronically exposed to low daily doses of 60Co γ rays (7.5 cGy/22 h/day) show one of three hematopoietic patterns, which reflect three different distinctly responding subgroups: (1) low radioresistance with progressing aplastic anemia and shortened survival ( −S-AA subgroup); (2) high radioresistance with a complex of progressing myeloproliferative disorders ( +R-MPD group); or (3) high radioresistance with other nonMPD syndromes ( +R-nonMPD group). Blood cell levels (granulocytes, monocytes, erythrocytes, lymphocytes, and platelets) were assessed and fitted to a flexible polynomial spline model, thus defining the (a) initial suppressive and (b) subsequent recovery phases for the subgroups. Results showed that relative to the overall magnitude of blood cell loss as well as to the maximum rate of suppression during the initial phase, the subgroups were generally ranked −S-AA ⪢ +R-MPD > +R-nonMPD . Relative to the overall strength of the recovery response, the subgroups were generally ranked +R-MPD > +R-nonMPD ⋙ −S-AA . In terms of overall maintenance levels of circulating blood cells during the recovery phase, however, the +R-nonMPD subgroup consistently exhibited stronger responses than the +R-MPD subgroup. These results tend to support our contention that selected subgroups of dogs have strong propensities to specific hematopathologies (i.e. aplastic anemia and myeloid leukemia) under chronic irradiation and that these pathology-prone animals exhibit a series of marked differential hematopoietic responses during early preclinical phases, which serve effectively to prognosticate subsequent pathological progression.