The effects of dose protraction on hematopoiesis in the primate and dog

The modifying effects of dose protraction by fractionation or continuous low dose-rate exposure are not well known in the primate. Comparative studies between the two mammalian species dog and monkey with widely differing acute LD50 values have not been made. A program to study dose-rate effects on injury and recovery of the bone marrow in dogs and monkeys under simultaneous and similar exposure conditions is in progress. The equivalent residual dose (ERD) assumptions of 10% irreparable injury and a 28-day recovery half-time for the reparable portion (90%) of radiation were studied in dogs (beagles) and monkeys (Macaca arctoides) using variable recovery times and appropriate fractionated exposures to attain but not exceed theoretical effective residual body burdens of 200 rads over a 1-year period. The ERD assumptions were tolerated by the dogs but resulted in death to 7 of 8 monkeys tested. The same ERD assumptions were tested with monkeys (Macaca mulatta) using a fixed recovery time span and an upper ERD limit of 100 rads. Monkeys in this study have tolerated 1900 rads of gamma-ray exposure (approximately 3 times the acute lethal dose) with minimal suppression of the hematopoietic system.