The effects of calcium antagonism on the epicerebral circulation in early vasospasm

We have studied the effects of the calcium antagonist verapamil on the epicerebral arteriovenous transit time and regional epicerebral circulation of dogs by direct measurement of arterial diameters, fluorescein angiography, and krypton-85 regional epicerebral blood flow analysis. A large craniectomy was performed and vasoconstriction was induced by the subarachnoid injection of human platelet-rich plasma (PRP) pretreated with 25 mu M of ADP to cause maximum aggregation. Once vasoconstriction was established, verapamil (0.1 mg/kg) was topically applied to the perforated arachnoid. The PRP-ADP produced a mean decrease in the arterial diameters of 38.2 +/- 1.6% (p less than 0.01) at 10 minutes after its injection and verapamil produced a mean dilatation of 19.5 +/- 2.5% (p less than 0.01), compared to control values. Regional epicerebral blood flow was 54.9 +/- 3.4 ml/100 g/min in the control state, 34.8 +/- 3.2 ml/100 g/min (p less than 0.01) during vasospasm, and 78.2 +/- 4.5 ml/100 g/min (p less than 0.01) after verapamil. Fluorescein angiography, after verapamil, demonstrated a mean acceleration of the arteriovenous circulation time of 4.5 +/- 0.8 seconds (p less than 0.01) compared to the spasm value. We concluded that the topical application of verapamil can dilate previously constricted cortical arteries and that this dilatation is associated with acceleration of the epicerebral transit time and increased cerebral blood flow.