Differences in the Effects of Anaesthesia on Hypoxia in Normal Tissues

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Abstract
Mice were anesthetized with sodium pentobarbitone (60 mg/kg). A 46 mm length in the mid-tail region was irradiated with 250 kV X-rays. Six or 8 animals at a time were strapped in a jig which was contained in a box 7.3 l in capacity, which was flushed with 5 l/min of O2 or air for 5 min before and during irradiation. A skin reaction started at about 12 days, reaching a peak between 20-30 days. Thereafter, the reaction subsided at a rate which was dose-dependent, and even after the highest doses was subsiding by 70 days after irradiation in animals which had not sustained permanent necrosis. Animals were irradiated after the base of the tails was clamped for 10 min with a rubber ring to occlude the blood supply. These animals were anesthetized during the clamping period and irradiation. The mice breathed air during these procedures, but N2 was passed over their tails for 5 min before and during irradiation. This procedure gave considerable protection to the skin of the tail, and the dose must be enhanced by a factor of 2.1-2.2 to give the same response as that observed in animals breathing O2. The ambient temperature during irradiations in these experiments was between 22-25.degree. C.