The effects of HA compound calcium antagonists on delayed cerebral vasospasm in dogs

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Abstract
✓ The authors have examined the effects of the HA compounds HA1004(N-(2-guanidinoethyl)-5-isoquino-linesulfonamide) and HA1077(l-(5-isoquinolinesulfonyl)homopiperazine), which are intracellular calcium antagonists, on delayed cerebral vasospasm from subarachnoid hemorrhage (SAH). The modes of action of these compounds were compared with those of the more commonly used calcium entry blockers. Calcium ionophore A23187 (4.8 × 10−6 M)-induced contraction of a canine basilar artery strip was completely antagonized by the HA compounds (10−5 M) but not by the entry-blocking calcium antagonists nicardipine, diltiazem, and verapamil (10−5 M), suggesting that the HA compounds act differently. Delayed cerebral vasospasm was induced by a “two-hemorrhage” canine model. The magnitude of the vasospasm and the effects of the HA compounds were determined angiographically. On SAH Day 7, a significant vasospasm was observed in every dog. The diameter of the basilar artery had diminished to 59% ± 2% (mean ± standard error) of the control value obtained before SAH (on Day 1). The intravenous administration of HA1004 caused a mild dilation of the basilar artery of 10% and 11% at doses of 3 and 10 mg/kg, respectively; however, HA1077 produced a more marked dilation of 19% and 27%, respectively, at the same doses. Both of these drugs lowered mean arterial blood pressure to about 80% and 50% at doses of 3 and 10 mg/kg, respectively. Intracisternal administration of the HA compounds (6 mg) completely reversed cerebral vasospasm without much effect on the blood pressure. The intracellular calcium antagonists of the HA compound group appear to be promising agents for the treatment of intractable cerebral vasospasm.