THE EFFECTS OF NALOXONE ON THE PERIPHERAL SYMPATHETICS IN CAT ENDOTOXIN-SHOCK

Abstract

The effects of naloxone on sympathetic nerve activity during Escherichia coli endotoxin hypotension were studied in .alpha.-chloralose anesthetized cats. Blood pressure and left preganglionic splanchnic nerve (PSN) activity were measured. Naloxone (2 mg/kg) was injected i.v. 30 min after the endotoxin. In the control group, 30 min after endotoxin administration mean blood pressure (MBP) and PSN activity decreased by 68 .+-. 7% and 47 .+-. 10%, respectively; after 60 min, MBP and PSN activity were 54 .+-. 8% and 48 .+-. 7% of the pre-endotoxin level. The reduced blood pressure recovered to 81 .+-. 4% of the pre-endotoxin level 5 min after naloxone injection. The naloxone-induced recovery of blood pressure was transient; a decline to the pre-naloxone level occurred .ltoreq. 30 min after the injection. The MBP was significantly higher than in the control group 60 min after endotoxin administration. There was a modest recovery in PSN activity (61 .+-. 7% of the pre-endotoxin level 5 min after naloxone administration) that was maintained for only 20 min. Three of 5 cats treated with an intermittent bolus injection (2 mg/kg, 30 min and 6 h after endotoxin) of naloxone survived, compared to only 1 of 5 nontreated cats. Thus, at least part of the beneficial cardiovascular actions of naloxone in treating endotoxin shock involves activation of the efferent sympathetic system. To improve long-term survival it may be necessary to continuously administer naloxone.