Radioemetic protection at 24 h after 60Co irradiation in both normal and postremectomized cats

The radioemetic dose-response relationships were established in 46 unanesthetized cats for each of two whole-body exposures, 24 h apart, to 60Co radiation at selected doses between 7.5 and 60 Gy. Individual episodes of vomiting were recorded for a period of 48 h as distinctive intrathoracic pressure deflections signaled through a catheter placed in the superior vena cava. Five cats with chronic lesions of the area postrema were included in the group exposed to 45 Gy. The lesioned animals were not detectably different in their radiation response behavior from the intact cats. Initial exposure in the entire cat series produced an increasing incidence of radioemesis from 25 to 80% over the specified dose range for the first observation period of 24 h. By contrast, the second exposure produced an inverse dose-related incidence of emesis varying from 63% to zero with an apparent crossover of radioemetic susceptibility for the two exposures at about 15 Gy. Complete protection during 12 h after the second exposure was obtained at 30, 45, and 60 Gy, and for all of 24 h at 45 and 60 Gy. In a separate group of 11 normal cats, the emetic drug xylazine invariably evoked vomiting when radioemetic protection was otherwise manifest after initial irradiation at 45 Gy. We conclude that the temporary recovery of well-being following acute lethal irradiation results selectively through increased radioemetic resistance, and it does not depend on the integrity of the area postrema.