The purpose of the present study was to examine the protective action of a 7.5% hypertonic NaCl solution (HS) on the circulatory shock produced by compound 48/80 (48/80) in rats and to determine the effect of the AV3V lesion on the protective action of HS. Intravenous injection of 48/80 into sham-operated rats resulted in an immediate drop of mean arterial pressure (MAP). In sham-operated rats, intravenous injection of HS prevented the drop of MAP produced by 48/80, but HS was ineffective in AV3V-lesioned rats. These results show that HS had a protective action on the circulatory shock produced by 48/80 and that the AV3V region plays an important role in this protective action.