Reaction of the vascular system in the trachea of the rabbit exposed to fractionated irradiation with and without the addition of misonidazole.

As the radiation field used in the radiation therapy of malignancies in the thoracic cavity often exposes the trachea to ionizing irradiation, it is important to ascertain the effects of radiation on this tissue either as a single therapy or in combination with radiosensitizers. In the study reported here the vascular area in the subepithelial layer of the trachea has been calculated in 160 rabbits treated in four ways: (1) 10 rabbits received no treatment and served as controls; (2) 50 rabbits were given 100 mg misonidazole daily on consecutive days, with the individual total dose ranging from 100 to 1000 mg; (3) 50 rabbits were treated with misonidazole in the same way, but were also exposed to radiation (2 Gy/F) at 15-30 min later; (4) 50 rabbits received only fractionated radiation (2 Gy/F). The total radiation dose in the irradiated animals ranged from 2 to 20 Gy. In the treated groups, an oedema was observed in both the ciliary cell layer and in the subepithelial area. In the group given only irradiation, this oedema was dose-dependent, but no such dose-dependency was observed in the two groups treated with misonidazole. The vascular area in the groups treated with misonidazole was significantly increased as compared with the group given only irradiation and the control group; this was valid both with and without correction for the oedema. There was a significant correlation between the oedema and the vascular area in the groups treated with misonidazole, which was not found in the group irradiated without the drug.