Summary
Human cells from the established line NHIK 3025 have been irradiated in suspension under extremely hypoxic conditions (<4 p.p.m. O2) and in presence of the organic nitroxyl-free radical TMPN (2,2,6,6,tetramethyl-4-piperidinol-N-oxyl), at four concentrations, viz. 0·5 mM, 1 mM, 3 mM and 10 mM.
TMPN was found to exhibit both a sensitizing and a protective effect. The sensitizing effect appears at high doses (>400–800 rads, dependent on TMPN-concentration) and increases with increasing TMPN-concentrations.
At low doses (<400–800 rads) TMPN was found to exert a protective effect. Below 300 rads, the protection was found to be optimal for a TMPN-concentration between 0·5 and 3 p.p.m. Within the concentration limits here studied it was found that the dose-range in which TMPN exerts a protection increases with decreasing TMPN-concentration.
The slope of the survival curves was found to increase when the dose exceeded about 2000 rads, irrespective of whether the cells were in contact with 1 mM, 0·5 mM or no TMPN. This suggests that TMPN does not affect the dose-level at which the medium effect appears. (Pettersen, Oftebro and Brustad, 1974.)