Pentobarbital anesthesia has been observed to increase markedly the effectiveness of respiration of
oxygen at 3 atmospheres of pressure absolute to increase the response of early generation isotransplants of C3H mouse
tumors to two-dose irradiation. A possible mechanism of this phenomenon is suppression of
oxygen utilization by the
pentobarbital and hence increasing mean pO2 and
oxygen diffusion lengths. Measurements of QO2 of
suspension of MCaIV and FSaII cells from freshly excised
tumor tissue have been measured for cells suspended in PBS, Hank's buffered with
HEPES +/-
glutamate. The
oxygen utilization by these
tumor cells in vitro (when measured at congruent to 10 minutes after excision) is low, viz. 1 nmole/min/mg
protein as compared with 6-9 nmoles/min/mg
protein for established cell lines cultured in vitro. The suppression of QO2 by 2mM
pentobarbital is less than 10%. This is a concentration of
pentobarbital that is judged to be close to that which obtains in the tissues of the animals in the radiation response assays.
Pentobarbital at .2mM did not change the cell survival characteristics of Chinese V79 cell spheroids irradiated in vitro. The results of these experiments do not indicate the suppression of
oxygen utilization is an important contributor to the observed phenomenon of the increased response of
tumors irradiated in mice respiring
oxygen at high pressure. The role of
hypothermia produced by the
anesthesia is under further study.