All  of the following  actions  of histamine are mediated through H1 receptors EXCEPT:
Release of EDRF from vascular endothelium resulting in vasodilation
Direct  action  on  vascular  smooth  muscle  causing vasodilation
Bronchoconstriction
Release of catecholamines from adrenal medulla
Both H1 and H2 receptors cause vasodilation. H1 receptors are present in the endothelium and cause vasodilation by releasing NO. However, H2 receptors are present on the smooth muscles and cause direct vasodilation.