Peptides readily penetrate the blood-brain barrier: uptake of peptides by synaptosomes is passive.
The intracarotid artery quick injection technique of Oldendorf was utilized to determine the Brain Uptake Index (BUI) of radio-labeled peptides in comparison with 3H2O or 14C-antipyrine as counterlabels. The normalized BUI values for 3H-MIF-I, 3H-alpha-MSH and 14C-AVP were 13.7, 9.6 and 13.0 respectively at 15 sec after injection consistent with their having readily penetrated the blood-brain barrier. The BUI values were similar, though somewhat increased, at 10 min postinjection consistent with their ready exit across the blood-brain barrier. At 15 sec after injection 0.5+/-0.1%/g brain of the originally injected peptide label was recovered; and 0.1+/-0.2%/g brain was recovered after 10 min. The label was distributed uniformly in the major brain regions at both times. However, the percentage of the originally injected label/g of pineal and pituitary gland tissue was 10-20 X increased as compared with the major brain regions as would be expected by their location outside the blood-brain barrier. The in vitro uptake of the radio-labeled peptides by synaptosomes prepared from the whole brain and the major brain regions was passive; it was not temperature dependent, nor was it Na+ dependent. However, the binding of the three peptides by the synaptosomes varied considerably: AVP greater than MSH greater MIF: 50 greater than 5 greater 1. The penetratin of the blood-brain barrier by the three peptides is consistent with their having CNS effects.
D000818:Animals; D000983:Antipyrine / Q000378:metabolism; D001127:Arginine Vasopressin / Q000378:metabolism*; D001692:Biological Transport; D001812:Blood-Brain Barrier; D001921:Brain / Q000378:metabolism; D009075:MSH Release-Inhibiting Hormone / Q000378:metabolism*; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D051381:Rats; D013574:Synaptosomes / Q000378:metabolism; D014667:Vasopressins / Q000031:analogs & derivatives*
D014667:Vasopressins; D001127:Arginine Vasopressin; D009074:Melanocyte-Stimulating Hormones; D009075:MSH Release-Inhibiting Hormone; D000983:Antipyrine