Evidence that halothane inhibits norepinephrine release from sympathetic nerve endings in dog saphenous vein by stimulation of presynaptic inhibitory muscarinic receptors.

Studies were done to determine the mechanism whereby halothane inhibits the release of norepinephrine from postganglionic sympathetic nerve endings. Helical strips of dog saphenous vein were mounted for superfusion and measurement of isometric contractile tension in the presence or absence of halothane (1.2 or 2.5%). Endogenous norepinephrine overflowing in response to electrical stimulation (10 V, 2 Hz for 15 min), and the content of norepinephrine remaining in the veins after stimulation, were measured by liquid chromatography with electrochemical detection. The data indicate that halothane decreased the stimulation-evoked release of norepinephrine by stimulation of prejunctional inhibitory muscarinic receptors. Evidence was also obtained that halothane may impair clearance of norepinephrine from the synaptic cleft.