Quantitative evaluation of α and β-adrenoceptor modulation of [3H] choline release in guinea pig superior cervical ganglia

[3H]Overflow evoked by 5 min supramaximal preganglionic stimulation at 1 pps has been studied in isolated guinea pig superior cervical ganglion prepartions preincubated with [3H]choline. At 15μM norepinephrine (NE) reduced both the [3H]choline overflow and endogenous acetycholine release by 59.4 and 54.1% respectively; the dose-response curve for NE inhibitory actions is described. Evidence is given that endogenous catecholamines effectively reduce ACh release from the ganglia. After blocking the inhibitory action of the endogenous NE, a significant B-adrenoceptor-mediated facilitatory effect on ACh release could be observed. Preincubation of the ganglia with different combinations of x1 and x2 agonists (phenylephrine, 10 μM and clonidine, 1 μM respectively) and antagonists (prazosin, 10 μM and yohimbine, 3 μM) showed that the adrenoceptors involved in x-mediated NE inhibition of ACh output are exclusively of the x2-type. (author)