The role of the host defense system in the development of cerebral vasospasm: Analogies between atherosclerosis and subarachnoid hemorrhage

Similar to atherosclerosis, platelet-derived growth factor (PDGF)-BB, a major growth factor for vascular smooth muscle cells, is produced in arterial walls to repair arteries after subarachnoid hemorrhage (SAH). On review of a series of research articles that focus on defensive host responses to SAH, PDGF-BB is identified as a spasmogen, based on the following findings: (1) foreign substances injected into the subarachnoid space cause persistent constriction of cerebral arteries with a time course and histological features almost identical to those seen after SAH; (2) persistent constriction induced by SAH or a foreign substance is dependent on the complement system; (3) the complement system, which stimulates platelets, macrophages and endothelial cells to secrete PDGF-BB, is activated in both the cerebrospinal fluid (CSF) and plasma immediately after SAH; (4) PDGF-BB levels in the CSF are significantly elevated in patients with delayed cerebral ischemia; (5) the immunodensity of PDGF-BB in the arterial walls correlates well with the severity of cerebral vasospasm; (6) intracisternal injection of PDGF-BB induces persistent constriction of cerebral arteries in a dose-dependent manner; (7) prolonged contact with blood clots promotes the contractile response of cerebral arteries to PDGF-BB, and (8) administration of an antagonist of PDGF-BB function suppresses the development of cerebral vasospasm.