Anisodamine , an alkaloid extracted from Anisodus tanguticus , is widely used in China in the treatment of septic shock, but its mechanism of action is unknown. We studied its antishock action in cats in a well controlled model of hemorrhagic shock. A bolus dose of 1 mg/kg was given intravenously 20 min after MABP was stabilized at 40-45 mm Hg, followed by i.v. infusion of 2 mg/kg/h during the oligemic period. Two hours post-reinfusion, MABP was significantly higher (106 +/- 10 mm Hg) in the drug-treated group than in shock cats receiving only vehicle (53 +/- 6 mm Hg, P less than 0.001). Anisodamine treated shock cats exhibited significantly lower cathepsin D activity (P less than 0.02) and amino-nitrogen concentration (P less than 0.001) than untreated shock animals. Plasma myocardial depressant factor (MDF) activity was significantly increased in the untreated shock cats (61 +/- 6 Units/ml), but the plasma accumulation of MDF was significantly blunted by anisodamine (32 +/- 5 Units/ml, P less than 0.01). Anisodamine did not increase superior mesenteric artery flow ( SMAF ) in this model of hemorrhagic shock as there was no significant difference in SMAF between the two shocked groups. Thus, the beneficial effect of anisodamine probably is not due to vasodilation of the splanchnic vasculature. In vitro analysis indicates that the drug has a direct anti-proteolytic action in cat pancreatic homogenates. This may partly explain the mechanism of its action, which appears to be complex.