Background: Histamine plays a role in postasphyxial brain oedema formation. We investigated the effect of intracarotid histamine injection on blood-brain barrier permeability (BBBP) and acid phosphatase (APase, EC 3.1.3.2) activity in brain tissue and isolated cortical microvessels (MV).

Subjects: 48 anesthesized newborn pigs (4-8 h; 1,070-1,560 g).

Methods: Histamine, in doses of 0, 10-4, 5x10-4, 10-5, 5x10-5 and 10-4 M was injected into left internal carotid artery. One h after the challenge, BBBP for a small (sodium fluorescein, SF, 376 Da) and a large (Evans blue-albumin, EB, 67 kDa) tracer was determined in frontal, parietal, occipital cortex, hippocampus, and periventricular white matter of both hemispheres. BBBP was quantified by fluorometry (excitation: 440 nm, emission: 525 nm for SF; 620 nm and 680 nm for EB, respectively). APase enzyme activity was measured by the rate of hydrolysis of p-nitrophenyl-phosphate in brain and isolated MV. Statistics: Kruskal-Wallis one-way ANOVA and Dunn's test.

Results: Histamine injection significantly (P<0.05) increased BBBP for both tracers in each brain region. Changes in left hemisphere were more intense (P<0.05) than those in right one. Similarly, histamine injection also increased total and tartrate-resistant APase activity in MV.

Conclusion: Histamine-induced increase in APase activity may contribute to the dose-dependent vasogenic brain oedema formation by the modulation of endocytic transport pathways in cerebral endothelium.