Soman intoxication and the blood-brain barrier.

Brain capillaries (microvessels) were isolated from rabbit brain. Morphological characterization revealed relatively pure fractions of microvessels consisting of the capillary endothelium, the basal membrane, and the pericyte. These fractions of brain capillaries show acetylcholinesterase (AChE) and monoamine oxidase (MAO) activity, but lack catechol-O-methyltransferase and GABA transaminase activity. Isolated brain capillaries together with samples of the brain parenchyma and serum were used to study the role of AChE present in the brain capillary wall in soman intoxication. The results showed this AChE to be less sensitive to soman inhibition than AChE of brain parenchyma. Serum and brain AChE recovered to some extent in soman-intoxicated rabbits given HI-6, whereas AChE present in the microvessel was even further inhibited. It is suggested that soman-induced vasospasm in rabbit brain may explain both the inaccessibility of capillary AChE to soman and also the unfavorable effect of HI-6 on this enzyme.