Mechanism of Selective Inhibition of Yohimbine and Its Derivatives in Adrenoceptor α2 Subtypes

Table 1

The alkaloids with AR blocking activities.

Name	Structure	Activities on ARs
(−)-Discretamine		α1D-AR blocking(rat) [7–9]; Selectivity among various α1-AR subtypes(rat): α1A : α1B : α1D = 0.04 : 0.07 : 1.0
Govadine		Selective α1-AR antagonist, α1 > α2 > β [10]
THB^1
Xylopinine		α-Receptor blocker
Berberine		α1, α2 Anatagonist; analgesic; antihypertensive; hypnotic; hypoglycemic; increases tolerance to anoxia; local anesthetic; reduces intraocular pressure (rabbit); vasodilator, vascular smooth muscle relaxant; smooth muscle stimulant
Jatrorrhizine		Antiarrhythmic; bidirectional action to heart (frog heart in vitro, inhibits first and then stimulates); antihypertensive; inhibits adrenaline(anesthetic rbt, iv); sedative(animal model); treatment of myocardial infarction (in coronary artery-ligated rbt)
Yohimbine		Antidiuretic; antiadrenaline; mydriatic; serotonin antagonist; High affinity for the α2-AR, moderate affinity for the α1-AR; Higher binding affinities at the α2C versus α2A and α2B [11]; α2A/α2B = 4.8 [12]; Binding affinities α2C (0.88 nM) > α2A (1.4 nM) > α2B (7.1 nM) [13]
Renoxidine		Antiadrenergic; anticonvulsant; antineoplastic; sedative; antihypertensive
Xylopine		α1-AR blocker; analgesic; CNS depressant; platelet aggregation inhibitor
Isocorydine		Adrenergic antagonist; antiarrhythmic (animal model); increases coronary flow and cerebral blood flow

1(+/−)-2,3,10,11-Tetrahydroxy tetrahydroprotoberberine HBr.