Naloxone attenuates hypoxic depression of ganglionic transmission

The effect of the opioid antagonist naloxone on hypoxia-induced blockade of synaptic transmission in the superior cervical ganglion (SCG) of the rat was studied in vitro. Naloxone (6 X 10(-6) M or more) attenuated the hypoxia-induced blockade of synaptic transmission in the SCG. In addition, in the concentrations studied, naloxone itself had a blocking effect on ganglionic transmission that involved terminal sites of the preganglionic axons. These data suggest that the protective effect of higher doses of naloxone on the hemodynamic responses to hypoxemia or ischemia may originate at least in part from the attenuating effect of naloxone on the hypoxia-induced blockade of ganglionic transmission.