A study on the radiation effect on microvasculature of N-methyl-N-Nitrosourea-induced mammary carcinoma in rats

ABSTRACT

Mammary carcinoma was induced in rats by itravenous injection of N-methy-N-Nitrosourea. Microangiography was perfromed to evaluate the microvascular alterations in mammary carcinoma after irradiation. The tumors were givena single dose of 1.400 rads using Co-60 telethrapy unit with field size of 4 x 4 cm at 40 cm SSD. The dose ratewas 147.5 rads per minute. Microangiography was performed prior to irradiation and at one, two, and four weeksfollowing irradiation. The results are as follows: 1. Before irradiation, mammary carcinoma in rats tended to formlobules and the basic vasculature consisted of peripheral vascular pattern with central penetrating vessels. Theperipheral vascular pattern was always richer than that of the center. Irregular and tortuous vessles stretchedfrom the periphery into the center of lobule. 2. One week following irradiation, an increase in the number ofsmaller, tortuous vessels and decreased intervasular distance were obseved in the central portion of each lobule.This finding seems to be due to an improved filling of some previously existing but unfilled vessels. This maylead to improved metabolic changes and reoxygenation. 3. Later's changes of microvasculature after irradiation aretortuosity, irregularity, narrowing, abrupt tapering, fragmentation, and extravasation. These findings progressedafter a lapse of time. 4. The results can be considered as the microangiographic demonstration of the fact that reoxygenation after irradiation is mainly due to dilatation of the collapsed tumor vessels.