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Kentaro Mori, Masahiro Miyazaki, Yasukazu Hara, Yasuhisa Aiko, Takuji Yamamoto and Yasuaki Nakao

Object

The extracellular Mg++ has a vasodilatory effect on the cerebral artery. The present study investigated the effect of intracisternal injection of MgSO4 solution on cerebral vasospasm in a canine model of subarachnoid hemorrhage (SAH).

Methods

Subarachnoid hemorrhage was induced in 10 beagles using the two-hemorrhage model. Angiography of the vertebrobasilar artery was performed on Day 1 (baseline values before SAH) and on Day 7 (during cerebral vasospasm after induced SAH) before and after intracisternal injection of 0.5 ml/kg of 15 mmol/L MgSO4 solution into the cerebellomedullary cistern.

Results

The cerebrospinal fluid Mg++ concentration was significantly increased to 3.15 ± 1.14 mEq/L after intracisternal injection from the preinjection value (1.45 ± 0.09 mEq/L; p < 0.01). The diameters of the basilar artery, vertebral artery, and superior cerebellar artery on Day 7 were significantly decreased to 58.0 ± 10.9%, 71.0 ± 10.1%, and 60.9 ± 13.8%, respectively, of their baseline diameters on Day 1 (p < 0.01). After intracisternal injection of MgSO4, these diameters significantly increased to 73.8 ± 14.3%, 83.0 ± 14.8%, and 74.1 ± 13.5%, respectively (p < 0.01).

Conclusions

Intracisternal injection of MgSO4 solution causes significant dilation of spastic cerebral arteries in the canine two-hemorrhage model of SAH.

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Kentaro Mori, Takuji Yamamoto, Masahiro Miyazaki, Yasukazu Hara, Yasuhisa Aiko, Nobuhiro Koike, Shinsuke Sakamoto, Yasuaki Nakao and Takanori Esaki

Object

The optimal CSF Mg++ concentration for vasodilation of spastic cerebral arteries after subarachnoid hemorrhage (SAH) and its duration are unknown. The temporal profile of the vasodilatory effect and optimal CSF Mg++ concentration after the intracisternal injection of MgSO4 solution were investigated in an SAH model in canines.

Methods

Cerebral vasospasm was induced by experimental SAH using a 2-hemorrhage model in 26 female beagles. On Day 7, 0.5 ml/kg of 15, 10, 5, or 0 mmol/L MgSO4 in Ringer solution was injected into the cerebellomedullary cistern. Angiography was performed on Day 1 (before SAH) and before and 1, 3, and 6 hours after the intracisternal injection on Day 7 to measure arterial diameters of the basilar artery (BA), superior cerebellar artery (SCA), and vertebral artery (VA). Cerebrospinal fluid Mg++ was also measured at the same time.

Results

Arterial diameters of the BA, SCA, and VA were significantly decreased by vasospasm on Day 7. Arterial diameter ratios (ratio of arterial diameter after MgSO4 injection to diameter before injection on Day 7) of the BA and SCA at 1 and 3 hours after and the VA at 1 hour after intracisternal injection of the MgSO4 solution were positively correlated with the CSF Mg++ concentration. All arterial diameter ratios, except 1 point of the SCA, exceeded 1 if the CSF Mg++ concentration was > 3 mEq/L at 1 hour after injection. Animals with CSF Mg++ concentrations > 3 mEq/L at 1 hour after injection (11 dogs) showed significantly increased arterial diameters of the BA at 1 and 3 hours after and of the SCA and VA at 1, 3, and 6 hours after injection, as compared with the diameters before injection. The CSF Mg++ concentration significantly increased at 1 hour (3.73 ± 0.69 mEq/L, p < 0.01) and 3 hours (2.05 ± 0.35 mEq/L, p < 0.01) after the intracisternal injection as compared with the baseline value (1.41 ± 0.20 mEq/L).

Conclusions

The reversible effect of an intracisternal injection of MgSO4 solution on the spastic artery requires CSF Mg++ concentrations > 3 mEq/L. The vasodilatory effect continues for 3–6 hours after injection. These results suggest that the continuous infusion or intermittent intracisternal injection of MgSO4 is needed to maintain the optimal CSF Mg++ concentration and constantly ameliorate cerebral vasospasm.