Pharmacology All of the following actions of histamine are mediated through H1 receptors EXCEPT: A Release of EDRF from vascular endothelium resulting in vasodilation B Direct action on vascular smooth muscle causing vasodilation C Bronchoconstriction D Release of catecholamines from adrenal medulla 💡 Explanation All of the following actions of histamine are mediated through H1 receptors EXCEPT: ✓ Correct Answer: B. Direct action on vascular smooth muscle causing vasodilation