Interaction of berberine with human platelet α2 adrenoceptors

Berberine was found to inhibit competitively the specific binding of [3H]-yohimbine. The displacement curve was parallel to those of clonidine, epinephrine, norepinephrine, with the rank order of potency (IC50) being clonidine > epinephrine > norepinephrine (14.5 μM) = berberine. Increasing concentrations of berberine from 0.1 μM to 10 μM inhibited [3H]-yohimbine binding, shifting the saturation binding curve to the right without decreasing the maximum binding capacity. In platelet cyclic AMP accumulation experiments, berberine at concentrations of 0.1 μM to 0.1 mM inhibited the cAMP accumulation induced by 10 μM prostaglandin E1 in a dose dependent manner, acting as an α2 adrenoceptor agonist. In the presence of L-epinephrine, berberine blocked the inhibitory effect of L-epinephrine behaving as an α2 adrenoceptor antagonist