TY - JOUR T1 - Blockade of ganglionic afterdischarges by tyramine may be mediated by endogenous catecholamines. JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 376 LP - 379 VL - 228 IS - 2 AU - D Christ AU - T Zitaglio Y1 - 1984/02/01 UR - http://jpet.aspetjournals.org/content/228/2/376.abstract N2 - Tyramine reduced the compound postganglionic action potential from preganglionic stimulation of the golden hamster isolated stellate ganglion at 0.2 Hz. This action of tyramine was only slightly reduced by phentolamine (10(-5)M), an alpha adrenoceptor antagonist. Tyramine also reduced the postganglionic discharges after preganglionic stimulation at 30 Hz for 2 sec in the presence of hexamethonium. The blockade of afterdischarges by tyramine was markedly reduced by phentolamine. Furthermore, tyramine was much less effective in blocking ganglia from reserpine-pretreated hamsters (6 mg/kg, 4 hr before isolation). Blockade of afterdischarges by norepinephrine was reduced by phentolamine, but not by reserpine. These results indicate that the blockade of afterdischarges with tyramine is mediated by endogenous catecholamines. The blocking action of tyramine was not reduced by cocaine (10(-5)M). Cocaine did reduce the afterdischarges, and this action of cocaine was partially antagonized by phentolamine and reserpine. These results suggest that the blockade of afterdischarges by tyramine and cocaine is due to inhibition of catecholamine uptake which potentiates the actions of endogenous catecholamines. ER -