Absence of protective role of afferent nerves in early intestinal mucosal alterations induced by abdominal irradiation in rats

Purpose: To assess the early effects of primary afferent nerve suppression by systemic treatment with the neurotoxin capsaicin in an acute model of ab dominal irradiation in rats (10 Gy, gamma). Materials and methods: Changes in myeloperoxidase (MPO) activity, calcitoni n gene-related peptide (CGRP) tissue content, number of mast cells and apop totic cells were determined in jejunum and ileum in four groups of rat male Wistar (vehicle sham-irradiated, vehicle irradiated, capsaicin sham-irradi ated and capsaicin irradiated) at 1 and 3 days post-irradiation. Results: In vehicle irradiated rats, CGRP was significantly increased from the first day after irradiation in jejunal mucosa; MPO activity increased i n both segments at day 3 but not at day 1 after irradiation: the number of detectable mucosal mast cells dropped to nearly zero on days 1 and 3, while the apoptotic cells in the intestinal mucosa were significantly increased at day 1. Similar results were obtained for mast cells and apoptosis in cap saicin irradiated rats as compared to capsaicin sham-irradiated rats, while MPO activity was significantly increased and CGRP concentration in jejunal mucosa significantly decreased from the first day in these rats in compari son with capsaicin sham-irradiated rats. Conclusions: Intestinal sensory innervation seems not to have a major prote ctive role against a radiation-induced intestinal inflammatory reaction.