Guanethidine Sulfate is an anti-hypertensive drug involved in reducing the release of catecholamines such as norepinephrine [1].
In vitro: Guanethidine (0.1 and 1 μM) decreased S-I efflux but increased resting efflux in a concentration dependent manner[1].On the electrically stimulated mouse vas deferens, Guanethidine (3 μM) treatment inhibited twitching by 95% ± 3% in 15 min, but this effect was only partially reversed after 1 h of washing (33% ± 12% of control). When guanethidine were used in combination with prilocaine, a reversal of 80% ± 13% (at 1 h) was observed. When co-incubated with guanethidine (3 μM), the twitch was reduced to 24% ± 4% of control and was reversed to 77% ± 7% after 1 h. The reversal produced by the combination was significantly more intense (P < 0.05) when compared with guanethidine alone. Local anesthetics reduced the sympatholytic actions of guanethidine, and this could explain the variable efficacy of guanethidine in the treatment of complex regional pain syndrome [2].
References:
[1]. Fabiani ME1,Story DF. Inhibition of sympathetic noradrenergic transmission by guanabenz and guanethidine in rat isolated mesenteric artery: involvement of neuronal potassium channels.Pharmacol Res.1996 Mar;33(3):171-80.
[2]. Joyce PI1,Rizzi D,Caló G,Rowbotham DJ,Lambert DG. The effect of guanethidine and local anesthetics on the electrically stimulated mouse vas deferens.Anesth Analg.2002 Nov;95(5):1339-43, table of contents.