Radio! Oncol 199.5; 29: 207-10. Changesin somecollon mwosal cells after Irradiation Ruda Zorc-Pleskovic Institute of Histology and Embriology, Medical Faculty, University of Ljubljana, Slovenia The aim of the present investigation was to study the histological and stereological changes in lymphocytes and mast cells after irradiation. For experimental model we used 20 Beagle dogs, 1-2 years old. Ten dogs were irradiated 20 days with 32 Gy onto the whole pelvis and tail. Another JO dogs represented a control group. Histological and stereological analysis were performed on a Wild sampling microscope M 501. In the nonirradiated group volume, numerical density and average volume of lymphocytes were significantly lower in comparison with the irradiated group. Volume density and average volume of mast cells were significantly lower in nonirradiated group. Numerical density of mast cells in this group was significantly higher. The results of our experiments show that mast cells and lymphocytes in the intestinal mucosa are deeply involved in the tissue fibrosis occurring as the response to irradiation. Key words: colon-irradiation effects; intestinal mucosa-pathology Introdnction Several years after irradiation severe fibrous changes of the colon often cause for a surgeon an unsolvable problem in surgical intervention. The purpose of our study was to investigate experimentaly the histological and stereological changes in the colon occuring after irradiation in view of an early diagnosis and prevention of fibrosis. The intestinal epithelium is a tissue most sensitive to irradiation.''2 3 Individual cells in the intestinal mucosa such as lymphocytes and mast cells participate in the defense system of the body or in the protection against Correspondence to: doc. dr. Ruda Zorc-Pleskovic, Institute of Histology and Embriology, Medical Faculty, University of Ljubljana, 61000 Ljubljana, Slovenia UDC: 616.348-001.29 tumor invasion. Therefore we paid special attention to them in our study. The literature data describe changes in the intestinal mucosa, 1 • 4' 5 6 yet no stereological data could be found in the available literature. Materials mid methods 20 Beagle dogs weighting 8 to 13 kg, 1 to 2 years old were included in our study. Ten dogs were irradiated (I) with y rays on telecobalt (Phillips) with 32 Gy over the pelvis region and tail. The size of the irradiated region on the skin was 10 x 15 cm. Ten dogs represented the nonirradiated group (N). Ten days after concluded irradiation, a 1-cm wide piece of colon transversum was excised from the middle third of the colon of the anesthetized dogs. Tissue was fixed in Bouin's fluid, embedded in paraffin 208 Zorc-Pleskovic R and cut in 5 ^m step serial sections. The step section was 20 ^m thick. The obtained preparations were stained with hematoxylin-eosin (HE), toluidine-blue and solution alcian blue (SAB) reaction. An accurate histological analysis of the step serial sections was used to establish the changes in the mucosa of the colon in individual groups. The lymphocyte infiltration and presence, size, form as well as distribution of the mast cell's granules were studied. Histological analysis7 were performed on a Wild sampling microscope, using Weibel's test system. Volume density (Vv) of lymphocytes and mast cells were estimated at an objective magnification x40 using the M-42 test system. Numerical density (Nv) of I and m were estimated according to the Weibel-Gomez method at an objective magnification x40 using the M-100 test system. For these cells average volume was also calculated. The results were statistically evaluated. Significant differences were determined by Student's "t" test. Results Histological analysis In the N group lymphocyte infiltration of lamina propria in the intestinal mucosa was well expressed while in the irradiated group (1) there were some rare lymphocytes only in the connective tissue. The individual ones infiltrated the epithelium (Figure 1). In the N group the mast cells were equally distributed in the connective tissue. Their cytoplasm was full of metachromatically stained granules. Oval nuclei were visible in the middle of cells (Figure 2). In the I group the mast cells were mainly in the connective tissue at a basal part of the cryptes. Their shapes were mainly irregular. Numerous metachromatic granules were dispersed around the cells (Figure 3). Stereological analysis In the N group all the measured stereological values of lymphocytes such as Vv (Figure 4), Nv (Figure 5) and average volume of the indi- Figure l. Rare lymphocytcs in thc irradiated group (HE, obj. 40x). Figure 2. Degranulatcd mast cells in the intestinal mucosa in the irradiated group (SAB, obj. 40x). VVl(mrrP) w 1 Figure 3. Volume density (Vv,) of lymphocytes in the nonirradiated (N) and the irradiated (I) group (Vv, ±2SE). P < 0.0001 Changes in some collon mucosal cells after irradiation 209 vidual lymphocytes Vj (Figure 6) were significantly lower in comparison with the I groups. Vv of mast cells (Figure 7) and Vm mast cells (Figure 8) were significantly lower, while the Nv (Figure 9) was significantly higher in the N group compared to the I group. Discussion Stereological analysis of lymphocytes after irradiation revealed reduction of Vv, Nv and V of lymphocytes. This demonstrates that irradiation reduces the number and the size of the cells. Nv|