Naloxone requires circulating catecholamines to attenuate the cardiovascular suppression of endotoxic shock

The opiate antagonist naloxone (NAL) improves cardiovascular performance in canine hemorrhagic and endotoxic shock. If the release of neural and adrenal catecholamines is attenuated, NAL does not produce the expected improvement in cardiovascular function in canine hemorrhagic shock. This study tests the hypothesis that an endorphin-catecholamine interaction at the heart is responsible for a part of the cardiovascular depression of endotoxic shock. Two groups of five dogs were instrumented to measure mean arterial pressure (MAP), the first derivative of left ventricular pressure over time (LV dP/dt max), cardiac output, and heart rate (HR); they were then subjected to bilateral adrenalectomy and given chlorisondamine to produce ganglionic blockade. At t = 0 min the dogs were given Escherichia coli endotoxin at 1 mg/kg (LD80). Group I animals received NAL at 2 mg/kg + 2 mg/kg.hr iv from t = 30 to t = 60. At t = 45 these animals were treated with epinephrine (EPI) at 20 micrograms/kg.hr iv until t = 60. Group II animals got EPI from t = 30 to t = 60 and NAL from t = 45 to t = 60 at the same doses as Group I. In Group I, NAL alone had no effect on MAP, LV dP/dt max, or HR. EPI significantly increased (P less than 0.002) cardiovascular parameters with MAP increasing from 52 +/- 7 to 159 +/- 14 mm Hg. In Group II, EPI produced a significant increase in all parameters, and the addition of NAL produced a further significant increase; MAP increased from 37 +/- 3 to 126 +/- 16 mm Hg with EPI and then to 175 +/- 11 mm Hg with NAL. These data support the above hypothesis and indicate that circulating catecholamines need to be present to allow naloxone to reverse the cardiovascular depression in endotoxic shock.