Substance P (NK1) receptor in relation to substance P innervation in rat duodenum after irradiation

It has previously been shown that high dose of irradiation to the rat abdom en leads to an increased level of substance P (SP) in the duodenum. In the present study the pattern of distribution of NK1 receptors (NK1-R) in rat d uodenum after irradiation (5-30 Gy), was examined at the same time-point (7 days) after irradiation, comparisons being made with the distribution of S P-innervation. Immunohistochemical methods were used. In controls, NR1-R-li ke immunoreactivity (-LI) was detected in epithelial cells, in cells in the region of the intestinal cells of Cajal within the deep muscular plexus (I CC-DMP), in neuronal cells in the myenteric plexus, and variably in granulo cytes in the mucosa. Irradiation with 5-10 Gy did not lead to obvious chang es in the pattern of NK1-R-LI. After irradiation with the highest doses (25 -30 Gy), the mucosa was often gravely damaged, displaying granulation tissu e. No epithelial NK1-R-LI was detected in this tissue, but was present in l ess affected mucosa after these doses. In the region of the ICC-DMP, in the myenteric plexus, and in granulocytes, NK1-R-LI was detected also after hi gh dose irradiation. However, the degree of NK1-R-LI in the region of the I CC-DMP was somewhat lower than seen in controls and after low doses. SP-imm unoreactive nerve fibers were present in the regions where NK1-R-LI was det ected. These findings support a suggestion that an increased level of SP af ter irradiation may contribute to the dose-dependent gastrointestinal adver se effects that occur after radiotherapy. (C) 2001 Elsevier Science B.V. Al l rights reserved.