A Comparison of the Radiation Response of the Epidermis in Two Strains of Pig

The response of the epidermis was compared in two strains of pig, the English Large White and the Göttinger Miniature, after irradiation with⁹⁰ Sr β rays. The effects of two types of anesthesia were also tested in pigs of each strain, a volatile gas mixture of ∼70% oxygen, ∼30% nitrous oxide, and 2% halothane, and an intravenously administered narcotic azaperon/etimodat with the animals breathing air. Strain- and anesthetic-related changes were compared on the basis of dose-effect curves for the incidence of moist desquamation from which ED₅₀ values (±SE) were determined, i.e., the dose required to produce this effect in 50% of the fields irradiated. For English Large White pigs anesthetized with the volatile gas mixture, an ED₅₀ of 27.32 ± 0.52 Gy was obtained for moist desquamation. Irradiation with the azaperon/etomidat anesthesia in this strain of pig produced a significantly higher ED₅₀ of 33.36 ± 0.76 Gy (P < 0.001). This appeared to be related to the fact that the animals were breathing air, i.e., a lower oxygen concentration (∼21%), at the time of irradiation. For the Göttinger Miniature pig the ED₅₀ values for moist desquamation were 38.93 ± 3.12 Gy and 43.36 ± 1.34 Gy while using the gaseous anesthetic mixture and the azaperon/etomidat anesthesia with the animals breathing air, respectively. These ED₅₀ values are 10-11 Gy higher than those obtained for the English Large White pig under identical conditions of anesthesia, which resulted in a strain difference ratio of ∼1.35. Radiation under the volatile gas mixture anesthesia resulted in a uniform irradiation response over the skin of the flank in both strains of pig. Radiation under azaperon/etomidat anesthesia resulted in a nonuniform skin response over the flank. The ED₅₀ for moist desquamation was significantly higher in dorsal sites on the flank compared with the ventral area of English Large White pigs; a similar trend was seen in Göttinger Miniature pigs. This difference in the radiosensitivity over the flank skin while the animals are under azaperon/etomidat anesthesia at the time of irradiation was associated with the animals breathing air and is in agreement with findings published previously for animals under halothane anesthesia and breathing air.