QF0301B is a potent α1-adrenergic receptor antagonist with inhibitory effects on α2-adrenergic receptors, 5-HT2A and histamine H1 receptors.

Adrenoceptor:

QF0301B exhibits marked α1-adrenoceptor blocking activity in isolated rubbed rat aorta rings, with a pA2 value of 9.00±0.12. In electrically stimulated rat vas deferens, QF0301B reverses and competitively antagonizes the inhibitory action produced by clonidine. Additionally, it inhibits the force and rate of contraction in rat isolated atria (pA2=5.91±0.43), competitively antagonizes the contractile effect of 5-HT in rat aorta (pA2=6.75±0.06) and in rat stomach fundus (pA2=7.13±0.48), as well as the contractions induced by histamine in isolated guinea pig longitudinal ileal muscle (pA2=7.40±0.40). QF0301B shows noncompetitive low action in 5-HT3, muscarinic, and nicotinic receptors, as well as Ca2+ antagonist[1].

QF0301B (0.1-0.2 mg/kg iv) induces a significant and prolonged decrease in mean arterial blood pressure accompanied by bradycardia. It does not significantly alter the cardiovascular effects of either 5-hydroxytryptamine (serotonin, 5-HT, 75 mg/kg iv) or the selective α2-adrenoceptor agonist B-HT 920 (0.2 mg/kg iv). However, QF0301B markedly inhibits the hypertensive effect of noradrenaline (5 mg/kg iv), a nonselective α-adrenergic receptor agonist[1].