LIGHT DYE MICROVASCULAR INJURY ELIMINATES PIAL ARTERIOLAR DILATION INHYPOTENSIVE PIGLETS/

Cerebral vasodilation in response to hypotension is necessary to maint ain adequate cerebral blood flow. This study in newborn pigs examines the hypothesis that endothelial injury in vivo inhibits cerebral vasod ilation in response to hypotension in newborn pigs, thus suggesting th at this response is endothelium dependent. Chloralose-anesthetized pig lets with closed cranial windows were studied before and after injury caused by light/dye or before and after dye only sham control. Light/d ye injury was produced by injecting sodium fluorescein i.v. and passin g filtered light from a mercury are lamp though the cranial window. Me asurements of pial arteries and arterioles were made during normotensi ve and hypotensive periods. Hemorrhagic hypotension (to 50% of the mea n arterial control value) caused pial arterial and arteriolar diameter s to increase 49 +/- 8% and 66 +/- 8%, respectively. After the light/d ye injury, dilation in response to hypotension was absent, whereas dil ations in response to isoproterenol and constriction in response to hy pertension (3.33 to 4.0 kPa increase in arterial pressure) and hypocap nia were retained. These findings are consistent with the hypothesis t hat hypotension-induced cerebral arteriolar vasodilation is dependent on endothelial signals influencing adjacent smooth muscle.