Blood—Brain Barrier and Peptides

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Abstract
The brain is both the source and the recipient of peptide signals. The question is: Do endogenous, blood-borne peptide molecules influence brain function? Brain regions with the tight capillaries of the blood–brain barrier (BBB) extract low but measurable amounts of labeled peptide molecules from an intracarotid bolus injection. In the rat, the extraction fractions of β-casomorphin-5, DesGlyNH2-arginine-vasopressin, arginine-vasopressin, lysine-vasopressin, oxytocin, gonadoliberin, substance P, and β-endorphin, studied in this laboratory, range from 0.5% (substance P) to 2.4% (arginine-vasopressin). Extraction varies little among the 15 examined brain regions. As shown for arginine-vasopressin, the extracted peptides may be bound in part to specific binding sites located on the luminal membrane of the tight endothelial cells. Transport of peptide molecules across the BBB cannot be ruled out, but it is unlikely that endogenous peptides pass the BBB in physiologically significant amounts. In contrast, in br...