Guanoxabenz (Hydroxyguanabenz) hydrochloride is an α2 adrenergic receptor agonist, with a Ki of 4000 nM and the fully activated form 40 nM for an α2A adrenoceptor[1][2][3].

The formation of high-affinity Guanoxabenz binding seems to be inhibited by a series of N-hydroxyguanidine analogs to Guanoxabenz, as well as by a series of metabolic inhibitors that included allopurinol, 1-chloro-2,4-dinitrobenzene, 5,59-dithiobis-(2-nitrobenzoic acid), cibacron blue, phenyl-p-benzoquinone, didox, and trimidox. The formation of Guanoxabenz high-affinity binding is also inhibited in a time- and concentration-dependent fashion by preincubating the membranes with the LW03 N-hydroxyguanidine analogue of Guanoxabenz[1]. The spleen cytosolic fraction mediates the reduction of Guanoxabenz to guanabenz, the latter having an almost 100-fold higher affinity for rat alpha2A-adrenoceptors than Guanoxabenz itself[2].

Guanoxabenz and guanabenz are both known as centrally active antihypertensive drugs. High affinity Guanoxabenz binding is induced in rat brain membranes after addition of NADH or NADPH cofactors. The rat cerebral cortex contains an enzymatic activity that may activate Guanoxabenz leading to formation of a metabolite showing high affinity for alpha 2-adrenoceptors[3].Guanoxabenz (0.1-3 mg/kg, i.p.) causes a dose-related reduction in locomotor activity; a dose of 1 mg/kg is selected since this induces a pronounced and sustained behavioural hypoactivity[4].

References:
[1]. UhlÉn S, et al. Characterization of the enzymatic activity for biphasic competition by guanoxabenz (1-(2,6-dichlorobenzylidene-amino)-3-hydroxyguanidine) at alpha2-adrenoceptors. I. Description of an enzymatic activity in spleen membranes. Biochem Pharmacol. 1998 Nov 1;56(9):1111-9.
[2]. Dambrova M, et al. Characterization of the enzymatic activity for biphasic competition by guanoxabenz (1-(2,6-dichlorobenzylidene-amino)-3-hydroxyguanidine) at alpha2-adrenoceptors. II. Description of a xanthine-dependent enzymatic activity in spleen cytosol. Biochem Pharmacol. 1998 Nov 1;56(9):1121-8.
[3]. Dambrova M, et al. Characterization of Guanoxabenz reducing activity in rat brain. Pharmacol Toxicol. 1998 Oct;83(4):158-63.
[4]. P W Dettmar, et al. Neuropharmacological studies in rodents on the action of RX 781094, a new selective alpha 2-adrenoceptor antagonist. Neuropharmacology. 1983 Jun;22(6):729-37.