Angiotensin II‐induced microvascular responses in mouse brain

Abstract

Although angiotensin II (AngII)‐induced hypertension increases the risk for ischemic stroke, the mechanisms linking AngII to this cardiovascular disease remain poorly understood. We determined whether AngII (delivered over a 2 wk period with an Alzet pump) promotes leukocyte (LECA)‐ and platelet (PECA)‐endothelial cell adhesion in cerebral venules and/or alters blood brain barrier (BBB) permeability in C57Bl/6 (WT), AT1‐R−/− mice, and AT1‐R−/−‐>WT bone marrow chimeras (BMC). Intravital video microscopy was used to monitor blood cell adhesion from a cranial window. AngII infusion induced dose‐dependent (400‐2000 ng/kg/min) increases in mean arterial pressure (MAP), LECA, and PECA. AT1‐R−/−, AT1‐R−/−‐>WT BMC, and WT mice treated with Losartan (25 mg/kg/day) all exhibited no changes in MAP, LECA and PECA in response to AngII. BBB permeability, measured by Evans blue extravasation, was increased in response to AngII in WT and AT1‐R−/−‐>WT BMC mice, but not in AT1‐R−/− mice and WT mice treated with Losartan. These findings implicate AT1‐receptors (AT1‐R) on blood cells in the inflammatory and pro‐thrombogenic phenotype induced during AngII‐induced hypertension. The accompanying BBB dysfunction appears to involve AT1‐R on endothelial cells, rather than blood cells. (Supported by HL26441)