Histamine question


does anyone know why histamine can cause both vasodilation and bronchoconstriction?
This seems almost contradictory to be


Hi! Histamine works by causing an increase in calcium ion concentration in the airway smooth muscle cells, which stimulates their contraction (sarcomere) and hence promotes constriction of the airways.

In vasodilation/vasoconstriction, it’s a different mechanism which is out of the scope of the IMAT but histamine produces a positive inotropic effect via H2Rs. Both H1Rs and H2Rs (receptors) are present in the smooth muscle of blood vessels, and activation of those by histamine causes vasoconstriction or vasodilation, respectively. So the different receptors cause different responses. :))

Hope this helps!!