CAPILLARY BARRIER FOR DOPA IN BRAIN AND DIFFERENT ORGANS

In the endothelial cells of the brain capillaries there is found a dopa-decarboxylase, forming dopamine which is physically inable to pass through the capillary barrier. In this way an enzymatic barrier between blood and brain for dopa is established. Normally, systemically injected dopa is found as dopamine in the endothelial cells of the brain capillaries, and not in the surrounding brain cells. By means of a dopa-decarboxylase inhibitor the enzymatic barrier for dopa is broken, so that dopa is not found in the capillary endothelial cells, but in the brain cells. The capillary barrier for dopa varies in intensity from area to area. In hypothalamus it was found to be weak in the tubero-infundibulum as well as in the infero-medial and infero-posterior regions while it is much stronger in the superior and lateral parts. There appears to be a direct correlation between the vascular density and the intensity of the blood-brain barrier for dopa; the most imperious regions being the magnocellular areas of the supraoptic and the paraventricular nuclei. No regional correlation between the barrier permeability for dopa and catecholamine terminals' sensitivity to reserpine is found. The majority of the peripheral organs do not contain decarboxylase in their endothelium and dopa passes freely. The kidney capillaries (outside glomerular plexus) behave in the same manner as those of the brain. © 1969 Springer-Verlag.