Intra-arterial histamine increases blood-brain transport in rats.

The neurotransmitter histamine is located in multiple compartments in the brain and may influence cerebral vessels during some conditions. We made measurements of cerebrovascular transport of labeled sucrose, alpha-aminoisobutyric acid (AIB), and horseradish peroxidase during sustained infusion of histamine into the internal carotid artery of anesthetized rats. Histamine increased the rates of transport of sucrose and AIB up to 237% in several brain regions and in different areas of cerebral cortex. The effect was dose dependent, was reversible within 2 h, and was mediated primarily by histamine H2-receptors. An increase in cortical water content occurred, and electron microscopic examination revealed that perivascular astroglial processes were swollen. There was a twofold increase in the number of endothelial pits and vesicles in cortical capillaries perfused by histamine. We conclude that histamine can influence the function of the blood-brain barrier.