QF0301B is an α1 adrenergic receptor antagonist and a low α2 adrenoceptor, 5-HT2A, and histamine H1 receptor blocker.
In isolated rubbed rat aorta rings, QF0301B shows marked α1-adrenoceptor blocking activity, with a pA2 value of 9.00±0.12. QF0301B reverses and competitively antagonizes the inhibitory action produced by clonidine in electrically stimulated rat vas deferens and 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) and 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, or as Ca2+ antagonist[1].
QF0301B (0.1-0.2 mg/kg iv) can cause a pronounced and prolonged fall in mean arterial blood pressure accompanied by bradycardia. QF0301B does not significantly modify the cardiovascular effects of either 5-hydroxytryptamine (serotonin, 5-HT, 75 mg/kg iv) or the selective a2-adrenoceptor agonist B-HT 920 (0.2 mg/kg iv), but markedly inhibits the hypertensive effect of noradrenaline (5 mg/kg iv), a nonselective a-adrenergic receptor agonist[1].
[1]. Orallo F, et al. In vivo and in vitro pharmacological studies of a new hypotensive compound (QF0301B) in rat: Comparison with prazosin, a known α1-adrenoceptor antagonist. Vascul Pharmacol. 2003 Feb;40(2):97-108.