Preserved contractility without side bias in endovascular filament models for subarachnoid hemorrhage

Decreased vasoconstrictor responses in remote cerebral arteries after focal brain ischemia and reperfusion in the rat, in vitro

The effects of brain ischemia and reperfusion on smooth muscle function in remote cerebral and peripheral arteries are hardly known. Maximum vasoconstrictions (E(max)) caused by 120mmol/l KCl and 5-HT in endothelium-denuded ring preparations were measured in ischemic and control cerebral arteries of rats after a 1-h right middle cerebral artery occlusion followed by 0-min (I/NR) or 2-3-min (I/SR) reperfusion, and in peripheral arteries after I/SR. Surprisingly, vasoconstrictions to 5-HT and 120mmol/lK(+) were attenuated in remote brain vessels after I/SR, i.e. in the contralateral middle cerebral artery and the basilar artery, while I/NR depressed E(max) of 5-HT and high KCl only in the ischemic middle cerebral artery. Pretreatment with N-(2-mercaptopropionyl) glycine (MPG, 100mg/kg i.p.), a free radical scavenger, fully prevented the impairment of vasomotor function in the middle cerebral artery on both sides after I/SR. Moreover, vasomotor functions were normal in the coronary, renal and pulmonary arteries after I/SR. In conclusion, focal cerebral ischemia and reperfusion impaired vasoconstrictor responses in remote brain arteries of rats by a mechanism involving free radicals. The lack of similar effects in peripheral vessels indicates poor defence of brain arteries against remote injury caused by reactive oxygen species-dependent mechanisms.

Acute vasoconstriction: decrease and recovery of cerebral blood flow after various intensities of experimental subarachnoid hemorrhage in rats

OBJECT

Immediate vasoconstriction after subarachnoid hemorrhage (SAH) has been observed in a number of experimental studies. However, it has not yet been examined which pattern this acute-type vascular reaction follows and whether it correlates with the intensity of SAH. It was the purpose of the present study to vary the extent of SAH using the endovascular filament model of SAH with increasing filament sizes and to compare the course of intracranial pressure (ICP), cerebral perfusion pressure (CPP), and regional cerebral blood flow (rCBF).

METHODS

Male Sprague-Dawley rats were subjected to SAH using the endovascular filament model. Subarachnoid hemorrhage was induced using a 3-0, 4-0, or 5-0 Prolene monofilament (8 rats in each group). Eight animals served as controls. Bilateral rCBF (laser Doppler flowmetry), mean arterial blood pressure, and ICP were continuously monitored. Thereafter, the rats were allowed to wake up. Twenty-four hours later, the animals were killed, their brains were removed, and the extent of SAH was determined.

RESULTS

After induction of SAH, ICP steeply increased while CPP and rCBF rapidly declined in all groups. With increasing size of the filament, the increase of ICP and the decrease of CPP were more pronounced. However, the decline of rCBF exceeded the decline of CPP in all SAH groups. In a number of animals with minor SAH, an oscillating pattern of rCBF was observed during induction of SAH and during early recovery.

CONCLUSIONS

The disparity between the decline and recovery of CPP and rCBF suggests that acute vasoconstriction occurs even in SAH of a minor extent. Acute vasoconstriction may contribute significantly to a perfusion deficit in the acute stage after SAH. The oscillating pattern of rCBF in the period of early recovery after SAH resembles the pattern of synchronized vasomotion, which has been thoroughly examined for other vascular territories and may yield therapeutic potential.