Effect of vasodilating drugs on intracortical and extracortical vascular resistance following middle cerebral artery occlusion in cats.

In 24 lightly anesthetized cats acute cerebral infarction was produced by transorbital occlusion of the left middle cerebral artery. Pial artery pressure and blood flow were measured in the center of the middle cerebral artery territory, and changes of segmental resistance were determined upstream and downstream of the pial arterial recording site. After middle cerebral artery occlusion, pial arterial pressure fell from 59 to 13 mm Hg, and blood flow from 67.4 to 19.6 ml/100 gm/min. Downstream (intracortical) vascular resistance slightly decreased from 0.93 to 0.72 mm Hg X ml-1 X 100 gm X minute, and upstream (extracortical) resistance rose from 0.89 to 6.18 mm Hg X ml-1 X 100 gm X min. Before middle cerebral artery occlusion, intracarotid infusion of papaverine (625 micrograms/kg/min) and prostacyclin (500 ng/kg/min) caused a reduction of downstream resistance, and intracarotid infusion of nimodipine (670 ng/kg/min) reduced both downstream and upstream resistance. After vascular occlusion all three drugs reduced mainly upstream resistance but cerebral blood flow did not significantly improve because blood pressure also fell. Intracerebral steal phenomena were never observed.