Editing Histamine (section)

=== Vasodilation and fall in blood pressure ===
It has been known for more than one hundred years that an intravenous injection of histamine causes a fall in the blood pressure.<ref>{{cite journal | vauthors = Dale HH, Laidlaw PP | title = The physiological action of beta-iminazolylethylamine | journal = The Journal of Physiology | volume = 41 | issue = 5 | pages = 318–44 | date = December 1910 | pmid = 16993030 | pmc = 1512903 | doi = 10.1113/jphysiol.1910.sp001406 }}</ref> The underlying mechanism concerns both vascular hyperpermeability and vasodilation. Histamine binding to endothelial cells causes them to contract, thus increasing vascular leak. It also stimulates synthesis and release of various vascular smooth muscle cell relaxants, such as [[nitric oxide]], [[endothelium-derived hyperpolarizing factor]]s and other compounds, resulting in blood vessel dilation.<ref name="Abbas et al (2018). Cellular and molecular immunology p.447">{{Cite book |title= Cellular and molecular immunology | vauthors = Abbas A |publisher=Elsevier |year=2018 |isbn=978-0-323-47978-3 |pages=447}}</ref> These two mechanisms play a key role in the pathophysiology of [[anaphylaxis#Immunologic|anaphylaxis]].