The
opiate antagonist,
naloxone, was infused at 8 mg x kg-1 x h-1 in cats to determine its effect in
hemorrhagic shock. Hemorrhaged cats treated with
naloxone maintained postreinfusion mean arterial blood pressure at a higher value compared to those receiving only the vehicle. Final pressures were 77 +/- 9 mmHg for cats receiving vehicle compared to 120 +/- 6 mmHg for cats receiving
naloxone. These values represent 58 +/-7 and 98 +/- 6% of initial pressures for vehicle- and
naloxone-treated cats, respectively (P < 0.001).
Naloxone also moderated increases in circulating lysosomal
hydrolase activity (4- vs. 23-fold increase) and total plasma proteolysis (33 vs. 100% increase). Plasma
myocardial depressant factor activity was also significantly reduced in
naloxone-treated hemorrhaged cats compared to
shock cats given
0.9% NaCl (16 +/- 3 vs. 58 +/- 4 U, respectively; P < 0.001). Studies on cat papillary muscles demonstrated that
naloxone at concentrations slightly higher than estimated plasma values during
shock exerted a moderate positive inotropic effect. Our results show that
naloxone improved the hemodynamic and biochemical state of cats in
hemorrhagic shock. Inhibition of proteolysis and stabilization of lysosomal membranes appear to be ivolved in the protective action of
naloxone, along with the well-known
opiate-antagonistic action of this agent.