Inhibition of radioemesis by disruption of catecholamines in dogs.

Dogs were treated 30 min to 1 hr before X irradiation with α-methyl-p-tyrosine (114 mg/kg, iv) or 6-hydroxydopamine (2 mg/kg, iv). A third group of dogs was given a known antiradioemetic drug, haloperidol (0.25 mg/kg, im), to verify the sensitivity of the procedure. Irradiated but untreated controls were also used. Light methoxyflurane anesthesia was used for restraint during the exposure. Exposure dose was 800 rad kerma delivered at 50 rad/min to a 10 × 10-cm area covering the abdominal area from xiphoid to pubis. Haloperidol and 6-hydroxydopamine significantly (P < 0.05) reduced the number of emetic episodes and delayed the onset time to the first episode. α-Methyl-p-tyrosine caused no significant changes. The effectiveness of 6-hydroxydopamine indicates that catecholaminergic neurons are involved in radioemesis, whereas haloperidol and phenothiazine-derivative tranquilizers inhibit radioemesis by blocking catecholamine receptor neurons.