Immunohistochemical staining revealed the presence of platelet-derived growth factor (PDGF) B-type receptors on capillaries of normal rat brain. Furthermore, capillary endothelial cells isolated from rat brain and grown in tissue culture bound [125I]PDGF-BB but not [125I]PDGF-AA, suggesting that they expressed B-type, but not A-type, PDGF receptors. PDGF-BB and PDGF-AB, but not PDGF-AA, also stimulated incorporation of [3H]thymidine into these cells. Thus, rat brain capillary endothelial cells have functional B-type receptors, and thereby differ from endothelial cells derived from large blood vessels, that do not express PDGF receptors. Our data suggest a possible role for PDGF-BB as an angiogenic factor.

A fraction enriched in capillaries has been prepared from the guinea pig cerebral cortex. The purity of this fraction was checked by light-and electron-microscopic examination and by its high enrichment in alkaline phosphatase and y-glutamyl transpeptidase. In the capillary-rich fraction, the endogenous level of histamine was 1.9%' of that measured in the initial hornogenate. The histamine-synthesizing enzyme, L-histidine decarboxylase, and the metabolizing enzyme, histamine-N-rnethyltransferase, were barely detectable. In addition, histamine elicits a twofold stimulation in the accumulation of cyclic AMP in this capillary fraction with an EC,,, of 5 PM.

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