Abstract
Pial arterioles 30-50 μ m wide were monitored in vivo using a television - microscopy -image splitting technique. Topical angiotensin II constricted the vessels in dose dependent manner. Selective endothelial injury with a helium neon laser/Evans blue technique abolished modest responses to All and greatly reduced larger responses. Thus, All produces endothelium dependent constriction of arterioles in vivo in this portion of the brains micro vascular tree.