Equal contribution of increased intracranial pressure and subarachnoid blood to cerebral blood flow reduction and receptor upregulation after subarachnoid hemorrhage. Laboratory investigation.

OBJECT: Cerebral ischemia remains the key cause of disability and death in the late phase after subarachnoid hemorrhage (SAH), and its pathogenesis is still poorly understood. The purpose of this study was to examine whether the change in intracranial pressure or the extravasated blood causes the late cerebral ischemia and the upregulation of receptors or the cerebral vasoconstriction observed following SAH.
METHODS: Rats were allocated to 1 of 3 experimental conditions: 1) cisternal injection of 250 microl blood (SAH Group), 2) cisternal injection of 250 microl NaCl (Saline Group), or 3) the same procedure but without fluid injection (Sham Group). Two days after the procedure, the basilar and middle cerebral arteries were harvested, and contractile responses to endothelin (ET)-1 and 5-carboxamidotryptamine (5-CT) were investigated by means of myography. In addition, real-time polymerase chain reaction was used to determine the mRNA levels for ET(A), ET(B), and 5-HT(1) receptors. Regional and global cerebral blood flow (CBF) were quantified by means of an autoradiographic technique.
RESULTS: Compared with the sham condition, both SAH and saline injection resulted in significantly enhanced contraction of cerebral arteries in response to ET-1 and 5-CT. Regional and global CBF were reduced both in the Saline and SAH groups compared with the Sham Group. The mRNA levels for ET(B) and 5-HT(1B) receptors were upregulated after SAH and saline injection compared with the sham procedure. The effects in all parameters were more pronounced for SAH than for saline injection.
CONCLUSIONS: This study revealed that both the elevation of intracranial pressure and subarachnoid blood per se contribute approximately equally to the late CBF reductions and receptor upregulation following SAH.