X-IRRADIATION-INDUCED EMESIS IN SUNCUS-MURINUS

X-irradiation-induced emesis was investigated in Suncus murinus, a hou se musk shrew. Whole body X-irradiation caused emesis, and the calcula ted ED50 value that induced emesis in 50% of animals was 429 cGy. At t he irradiation dose of 800 cGy all the animals vomited 10.0 +/- 2.4 ti mes with a latency of 20.0 +/- 2.9 min. The emetogenic effect of X-irr adiation was dependent on the part of the body exposed. Abdominal X-ir radiation at 1000 cGy caused emesis in all animals studied, whereas th e same dose to the head had no emetogenic effect. We investigated seve ral prophylactic methods against X-irradiation-induced emesis. Surgica l vagotomy completely inhibited the emesis induced by 800 cGy X-irradi ation. Emesis was also prevented by the subcutaneous administration of tropisetron (ICS 205-930, a selective serotonergic 5-HT3 receptor ant agonist) with an ID50 value of 29 mug/kg. These results suggest that ( 1) suncus is a useful experimental animal for the study of radiation-i nduced emesis and the development of prophylactic drugs, (2) serotonin plays an important role in X-irradiation-induced emesis, and (3) X-ir radiation-induced emesis is very similar to that caused by cancer chem otherapeutic agents.