Extravasation of blood-borne immunoglobulin G through blood-brain barrier during adrenaline-induced transient hypertension in the rat

The effect of transient hypertension on blood-brain barrier (BBB) permeability, particularly on extravasation of immunoglobulin G (IgG), has not been fully understood. In the present experiment, we investigated the time course of endogenous albumin and IgG extravasation through BBB and the localization of extravasated IgG in brain parenchyma during adrenaline (AD)-induced transient hypertension in the rat by using Evans blue fluorescence, immunohistochemistry, and Western blot. The results showed that a bolus injection of AD (10 mug/kg) induced a transient elevation of arterial pressure lasting about 1 min. The endogenous albumin and IgG entered the brain parenchyma via BBB only when hypertension occurred. Electron microscopically, the IgG-like immunoreactivities were predominantly seen in the cytoplasm of endothelia of capillaries, pericytes, extracellular space of parenchyma, and the cytoplasm of glial cells. The results suggest that circulating IgG or antibodies might contact the structures of brain parenchyma through passage of BBB when its permeability is temporally changed by transient hypertension. This phenomenon implies a possible mechanism of pathogenesis for immune-mediated diseases in the brain.