title: Lung radioprotection by WR-2721 at low X-ray doses per fraction.
abstract: The response of mouse lungs to single doses and ten fractionated irradiations has been tested using breathing rate and lethality as assays for damage. The radioprotective effect of 300 mg/kg WR-2721 has been determined for mice breathing air or 10% oxygen. The protection factor was assessed from dose response curves obtained at monthly intervals from 24 to 48 weeks. A low protection factor (1.2-1.4) was observed for single doses in air or 10% oxygen and also for ten fractions in air. Considerably more protection was seen with ten fractions in mice breathing the reduced oxygen concentration (protection factors of PF = 1.5-1.7). It is postulated that the low PF values normally reported for lung are due to the naturally high oxygen concentration in all cells in this tissue. A fraction of the cells becomes sufficiently hypoxic in 10% oxygen to be susceptible to WR-2721 radioprotection. This subpopulation can then be detected with small X-ray fractions (less than or equal to 5 Gy) but not with large single doses.
mesh_terms: D004999:Amifostine / Q000627:therapeutic use*; D000818:Animals; D004307:Dose-Response Relationship, Radiation; D008168:Lung / Q000528:radiation effects*; D008171:Lung Diseases / Q000517:prevention & control; D008297:Male; D051379:Mice; D008808:Mice, Inbred CBA; D009946:Organothiophosphorus Compounds / Q000627:therapeutic use*; D010100:Oxygen; D011833:Radiation Injuries, Experimental / Q000517:prevention & control; D012119:Respiration
chemical_list: D009946:Organothiophosphorus Compounds; D004999:Amifostine; D010100:Oxygen