Plasticity of autonomic control of emesis in irradiated ferrets.

To investigate the plasticity of the emetic response to irradiation, five groups of ferrets (with the appropriate controls) had either the vagal or the splanchnic nerves transected and either were immediately irradiated under urethan anesthesia or were irradiated in a conscious state at 0.5-4, 4-9, and 24 h and 7 days after nerve transection. All the ferrets used in this study had the left carotid artery and the right jugular vein catheterized several hours before irradiation so that blood pressures could be monitored. In ferrets that were irradiated while anesthetized, bilateral abdominal vagotomy performed immediately before 6-Gy irradiation prevented emesis. Acute bilateral abdominal splanchnicectomy markedly reduced emesis in such cases but had no statistically significant effect in conscious ferrets. The incidence of emesis in conscious controls laparotomized 0.5-4 h before irradiation was 50% after 2 Gy and 100% after 6 Gy. Intact conscious controls were tested with 10 Gy only and showed a 100% incidence of emesis after this dose. Bilateral abdominal vagotomy, performed on ferrets 4-9 h before 8-Gy irradiation of conscious animals, markedly reduced the incidence of radiation-induced emesis. When performed 24 h before irradiation, it abolished emesis. In contrast, vagotomy was ineffective when performed 7 days before irradiation. The data suggest that, after 2-8 Gy, the vagi are the major emetic pathway in conscious ferrets and the splanchnic nerves may, under certain conditions, constitute second or alternate pathways.