Editing Vasospasm (section)

==Pathophysiology==
Normally [[endothelial cells]] release [[prostacyclin]] and [[nitric oxide]] (NO) which induce relaxation of the [[smooth muscle]] cells, and reduce aggregation of [[platelets]].<ref>{{Cite journal|last1=Yakubu|first1=MA|last2=Shibata|first2=M|last3=Leffler|first3=CW|date=1994|title=Subarachnoid Hematoma Attenuates Vasodilation and Potentiates Vasoconstriction Induced by Vasoactive Agents in Newborn Pigs|journal=Pediatric Research|language=en|volume=36|issue=5 |pages=589–594|doi=10.1203/00006450-199411000-00009|pmid=7877876 |s2cid=22708777 |doi-access=free}}</ref> Aggregating platelets stimulate [[Adenosine diphosphate|ADP]] to act on endothelial cells and help them induce relaxation of the smooth muscle cells. However, aggregating platelets also stimulate [[thromboxane A2]] and [[serotonin]] which can induce contraction of the smooth muscle cells.  In general, the relaxations outweighs the contractions.

In atherosclerosis, a dysfunctional endothelium is observed on examination. It does not stimulate as much prostacyclin and NO to induce relaxation on smooth muscle cells. Also there is not as much inhibition of aggregation of platelets. In this case, the greater aggregation of platelets produce ADP, serotonin, and thromboxane A2. However the serotonin and the thromboxane A2 cause more contraction of the smooth muscle cells and as a result contractions outweigh the relaxations.<ref>{{Cite journal|last1=Yakubu|first1=MA|last2=Leffler|first2=CW|date=September 1999|title=Regulation of ET-1 biosynthesis in cerebral microvascular endothelial cells by vasoactive agents and PKC|journal=American Journal of Physiology. Cell Physiology|language=en|volume=276|issue=2|pages=C300 - C305|doi=10.1152/ajpcell.1999.276.2.C300|pmid=9950756 }}</ref><ref>{{Cite journal|last1=Yakubu|first1=MA|last2=Shibata|first2=M|last3=Leffler|first3=CW|date=September 1995|title=Hematoma-induced enhanced cerebral vasoconstrictions to leukotriene C4 and endothelin-1 in piglets: role of prostanoids|journal=Pediatric Research|language=en|volume=38|issue=1|pages=119–123|doi=10.1203/00006450-199507000-00021|pmid=7478789 |s2cid=23885828 |doi-access=free}}</ref><ref>{{Cite journal|last1=Yakubu|first1=MA|last2=Shibata|first2=M|last3=Leffler|first3=CW|date=1994|title=Subarachnoid Hematoma Attenuates Vasodilation and Potentiates Vasoconstriction Induced by Vasoactive Agents in Newborn Pigs|journal=Pediatric Research|language=en|volume=36|issue=5 |pages=589–594|doi=10.1203/00006450-199411000-00009|pmid=7877876 |s2cid=22708777 |doi-access=free}}</ref>