The recovery of the proliferative response induced by butylated hydroxytoluene (BHT) was evaluated in the type 2 epithelial cell population of BALB/c mouse lung after X ray or fission neutron irradiation. Previous autoradiographic studies revealed that the proliferative changes in the lung 2 days after BHT administration were due primarily to type 2 alveolar cells. When given immediately before BHT, radiation caused a dose-dependent decrease in the BHT-induced proliferative response, measured by [14C]thymidine incorporation into DNA and by labeling studies. When the time between irradiation and BHT injection was lengthened, the proliferative response gradually returned in a dose-dependent manner. Dose-response curves were generated from these data, and the radiation response was characterized by the reciprocal of the slope of the exponential region of the curve, designated D0(PF). Two types of recovery processes were investigated. (i) When the BHT stimulus after a single dose of X rays was delayed, the D0 (PF) increased from 120 (immediate BHT stimulation) to 360 rad at 2 days and to 580 rad by 14 days. After fission neutron irradiation, the D0 (PF) value was 60 rad at both 0 (immediate BHT stimulation) and 2 days but increased to 345 rad by 14 days. (ii) Split-dose studies revealed a decline in the prolifeative response when the interval between 100-rad fractions was less than 12 hr. After that time, the proliferative response returned to control values (2 days) and by 7 days had almost doubled.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging