Mechanisms of Radiation-Induced Emesis

Nausea and vomiting following radiation exposure are factors which may seriously limit the ability of humans to perform in military situations and are side effects of such significance in radiation therapy that they may limit the patients acceptance of treatment regimes 1. At doses of 1.5 Gy approximately 50 of humans experience nausea and vomiting, while at 3.0 Gy the figure approaches 100 . While irradiation almost anywhere may produce symptoms, the upper abdomen is the most sensitive site. Dogs, cat and monkeys also vomit on exposure to ionizing radiation, although cats and monkeys are considerably more resistant than dogs and man. The present studies were designed to attempt to determine the roles of the area postrema and the vagus in radiation-induced- emesis by ablation and electrophysiological studies, and to test the effects of some drugs on the emetic response. In addition we have recorded from neurons in the dog area postrema, applying substances which may be emetic, in a attempt to determine which transmitters, peptides and hormones might function as chemical mediators of emesis. Finally we have tested the emetic effects of some of these substances given intravenously in awake dogs, with particular emphasis on study of the mechanism of action of emetic agents on the area postrema neurons. Keywords Radiation effects Therapy Vomiting agents Emesis.