Cerebral microvascular acid phosphatase isoenzymes may contribute to the histamine-induced changes in the blood-brain barrier permeability

It was previously suggested that lysosomes and lysosomal acid phosphatase e nzyme (AcP, orthophosphoric monoester hydrolase, EC 3.1.3.2.) might have in fluence on the blood-brain barrier (BBB) permeability. In the present study , we examined the effect of intracarotid histamine administration on the ac tivity of two AcP isoenzymes, lysosomal high molecular weight (HMW; mw > 10 0,000) and cytosolic low molecular weight (LMW; mw <20,000) isoforms, and o n the changes in BBB permeability for sodium fluorescein (mw: 376) and Evan `s blue-albumin (mw: 67,000) in newborn pigs. A marked, dose-dependent incr ease in the activity of LMW AcP and a moderate elevation in the activity of HMW AcP was found in isolated microvessels, but not in brain tissue, conco mitantly with a dose-dependent BBB opening for both tracers. It is proposed that HMW and LMW AcP isoenzymes may have a role in the regulation of the p ara- and transcellular BBB permeability.