Zlokovic B V, Segal M B, Davson H, Mitrovic D M
Department of Physiology, Faculty of Medicine Belgrade, Yugoslavia.
Regul Pept. 1988 Jan;20(1):33-44. doi: 10.1016/0167-0115(88)90055-9.
The cellular uptake at the blood-tissue interface of the blood-cerebrospinal fluid (CSF) barrier to tyrosyl-3,5-[3H]enkephalin-[5-L-leucine] (abbreviated to Leu-enkephalin) and of its synthetic analogue D-alanine2-tyrosyl-3,5-[3H]enkephalin-[5-D-leucine] (abbreviated to D-Ala2-D-Leu5-enkephalin) was studied in the isolated perfused choroid plexuses from the lateral ventricles of the sheep, using the rapid (less than 30 s), single circulation, paired-tracer dilution technique, in which D-[14C]-mannitol serves as an extracellular marker. Cellular uptake of peptides was estimated by directly comparing venous dilution profiles of [3H] and [14C] radioactivities in the absence and presence of unlabelled peptide, the N-terminal amino acid (L-tyrosine), the typical L-transport system substrate, 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid (BCH) and the inhibitor of aminopeptidase activity, bacitracin. The cellular uptake of both enkephalins was strongly (65-76%) but not completely inhibited by the addition of 5 mM unlabelled peptide to the bolus; the self-inhibition was significantly higher for D-Ala2-D-Leu5-enkephalin than for Leu-enkephalin. The addition to the bolus of L-tyrosine (5 mM), BCH (10 mM) or bacitracin (2 mM) reduced the 3H-radioactivity uptake by the choroid plexus of both enkephalins by 20-40%, the degree of inhibition being greater for [3H]-Leu-enkephalin than for its analogue. It is concluded that during single passage of enkephalins through the choroid plexus circulation, unidirectional uptake at the blood-tissue interface of the blood-CSF barrier consists of two components; a saturable component, which represents uptake of the intact peptide by the choroid epithelium, and a non-saturable component, which reflects enzymatic degradation of peptide in the blood and/or at the barrier, with a liberation of the N-terminal tyrosyl residue. Higher penetration of the blood-CSF barrier by D-Ala2-D-Leu5-enkephalin can be attributed to its greater resistance to hydrolysis.
利用快速（少于30秒）、单次循环、双示踪剂稀释技术，以D-[14C]-甘露醇作为细胞外标志物，研究了酪氨酸-3,5-[3H]脑啡肽-[5-L-亮氨酸]（简称为亮氨酸脑啡肽）及其合成类似物D-丙氨酸2-酪氨酸-3,5-[3H]脑啡肽-[5-D-亮氨酸]（简称为D-Ala2-D-Leu5-脑啡肽）在绵羊侧脑室分离灌注脉络丛血-脑脊液（CSF）屏障的血-组织界面处的细胞摄取情况。通过直接比较有无未标记肽、N端氨基酸（L-酪氨酸）、典型的L转运系统底物2-氨基双环(2,2,1)庚烷-2-羧酸（BCH）和氨肽酶活性抑制剂杆菌肽时[3H]和[14C]放射性的静脉稀释曲线，估算肽的细胞摄取量。向推注液中加入5 mM未标记肽可强烈抑制（65 - 76%）但未完全抑制两种脑啡肽的细胞摄取；D-Ala2-D-Leu5-脑啡肽的自身抑制作用明显高于亮氨酸脑啡肽。向推注液中加入L-酪氨酸（5 mM）、BCH（10 mM）或杆菌肽（2 mM）可使两种脑啡肽在脉络丛中的3H放射性摄取降低20 - 40%，[3H]-亮氨酸脑啡肽的抑制程度大于其类似物。得出结论，在脑啡肽单次通过脉络丛循环过程中，血-脑脊液屏障血-组织界面处的单向摄取由两个部分组成；一个可饱和部分，代表脉络丛上皮对完整肽的摄取，以及一个不饱和部分，反映血液中和/或屏障处肽的酶促降解，同时释放出N端酪氨酸残基。D-Ala2-D-Leu5-脑啡肽对血-脑脊液屏障的更高穿透性可归因于其对水解的更大抗性。
