Effect of naloxone on endotoxin-induced pulmonary platelet sequestration

The opiate antagonist, naloxone, has been shown to obviate hypotension and to improve survival of animals with shock induced by endotoxin, hypovolemia, and spinal transection. This study was done to evaluate the effects of naloxone on pulmonary platelet trapping (PPT) and on platelet aggregability in dogs with endotoxin shock. Dogs with 51Cr labelled platelets were treated with naloxone before and after induction of endotoxin shock. PPT was assessed by measuring 51Cr activity in lung and blood using a gamma scintillation counter. ADP induced platelet aggregability was measured in an aggregometer. PPT seen in endotoxin shocked controls was obviated by naloxone treatment; this effect was more pronounced in pretreated dogs. Naloxone treated animals did not show the increased platelet aggregability normally seen in endotoxin shocked dogs. These results suggest the applicability of naloxone therapy for adult respiratory distress associated with shock.