Transport, uptake, and metabolism of blood-borne vasopressin by the blood-brain barrier.
Transport, binding, and metabolism of [phenylalanyl-3,4,5,-3H(N)]arginine vasopressin (AVP) by the blood-brain barrier (BBB) was studied in adult guinea-pigs by means of a novel vascular brain perfusion (VBP)/capillary depletion technique and HPLC. A time-dependent, progressive brain uptake of 3H-radioactivity was measured over the 10 min period of VBP both in brain homogenates and in brain tissue depleted of cerebral microvessels. The unidirectional blood-to-brain transport constant, K(IN), estimated by multiple-time tissue uptake analysis of the homogenate and postcapillary supernatant, indicated that the BBB transfer rate for [3H]AVP (K(IN) = 2.37 +/- 0.25 microliters min-1 per gram brain homogenate) was almost 10 times higher than for simultaneously perfused [14C]sucrose, a cerebrovascular space marker. In contrast to homogenate and postcapillary supernatant, the [3H]radioactivity determined in the vascular pellet after dextran density centrifugation of the brain homogenate was very low and only somewhat higher than for [14C]sucrose. HPLC analysis of the perfused brain tissue revealed time-dependent degradation of the blood-borne neuropeptide. The percentage of intact [3H]AVP as determined in the postcapillary supernatant progressively declined during brain perfusion, from 49% at 1 min to 11.9% at 10 min. The major detectable labeled metabolite was [3H]phenylalanine, the labeled amino acid residue of [3H]AVP. The aminopeptidase inhibitor bestatin (0.5 mM), perfused simultaneously with [3H]AVP by the VBP technique, did not alter tissue uptake of [3H]AVP, indicating that there was no significant hydrolysis of peptide by the luminal BBB surface.(ABSTRACT TRUNCATED AT 250 WORDS)
Zlokovic
B V
BV
Department of Neurological Surgery, Childrens Hospital Los Angeles, University of Southern California.
Banks
W A
WA
el Kadi
H
H
Erchegyi
J
J
Mackic
J B
JB
McComb
J G
JG
Kastin
A J
AJ
D000818:Animals; D001127:Arginine Vasopressin / Q000097:blood* / Q000493:pharmacokinetics; D001692:Biological Transport / Q000502:physiology; D001812:Blood-Brain Barrier / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006168:Guinea Pigs; D008297:Male; D010477:Perfusion; D011485:Protein Binding; D012588:Scintillation Counting
D001127:Arginine Vasopressin