The Kinetics of Cellular Recovery in Locally X-Irradiated Rat Ileum

Abstract

treated and control animals were given tritiated thymidine ip and killed one hour later. The irradiated or sham-irradiated segment and segments of shielded intestine 5 cm and 10 cm distal to the irradiated or sham-irradiated segments were removed and appropriately processed for histologic and autoradiographic studies. At each time sampled, the number of total cells per crypt section in both the irradiated segment and the shielded segment 5 cm distally was greater than in the respective control segments. The differences between treated and control values decreased with time after irradiation. The percent labeled cells per crypt section for samples from the irradiated area and from the segment located 5 cm distally were not different from controls. The total cells, labeled cells, and percent labeled cells per crypt section in the segment located 10 cm distally were not different from the respective control values. The results obtained indicate that local irradiation of the intestine does not change the relative size of the proliferative compartment. This is in contrast to the situation which exists after whole-body exposure to 1000 R in which the entire crypt becomes proliferative. The mucosal cell proliferation rate is slightly increased in a shielded ileal segment 5 cm from the site of local irradiation, suggesting that there is an attempt by adjacent unirradiated tissue to compensate for the temporary loss of functional crypts. The compensatory increase in cellularity in both the irradiated and shielded intestine, followed by a decrease toward control values with time after irradiation and increased distance from the irradiation site, suggests a local, temporary influence associated with