Water permeability of capillaries in the subfornical organ of rats determined by Gd-DTPA^<2-> enhanced ^1H magnetic resonance imaging

本文用^1H核磁共振法测定了大鼠皮下器官（SFO）毛细血管水通透性，并与静脉注射不能通过血脑屏障（BBB）的舒张剂钆-二乙烯三胺-N，N，N '，N“，N”-五乙酸（Gd-DTPA^2）相结合。从Gd-DTPA^2在完整脑和血脑屏障通透脑中的剂量依赖性结果判断，Gd-DTPA^2不可能从皮质、丘脑或SFO的毛细血管漏出，但可能在垂体后叶外渗。在4.7T下用反转恢复磁共振成像测量了水在SFO区的纵向弛豫时间。T_1弛豫率（1/T_1）输注前为0.70 ^^+__-0.02 s ^<-1>（平均值为1.53 ^+_-0.11 s ^<-1>（n=9）。水流入毛细血管的速率常数估计为0.84 ^^+__-0.11 s ^<-1>（n=9），其对应于3.7 x 10^ cm s^的扩散膜渗透率（Pd）<-3><-1>。与文献中的值相比，SFO毛细血管的Pd值与直小血管水的跨膜渗透性的Pd值是同一数量级，并且可能比皮质中的血脑屏障的Pd值大10 - 100倍。皮层和丘脑的T_1弛豫率变化最小（约100%）。0.09s^<-1>），但这些不具有统计学显著性，这对应于Pd值远小于SFO中发现的Pd值。从这些结果中，我们得出结论，SFO中的毛细血管具有在SFO中的所有毛细血管中最高的水渗透性值之一，具有在脑中的所有毛细血管中最高的水渗透性值之一。本文还提出了基于T_1弛豫率的磁共振成像是一种原位检测局部透水性的有效方法

The water permeability of capillaries in the subfomical organ (SFO) of rat was measured by a ^1H nuclear magnetic resonance method in combination with a venous injection of a relaxation reagent: gadolinium-diethylene triamine-N,N,N',N",N"-pentaacetic acid (Gd-DTPA^2), which could not pass through the blood-brain barrier (BBB). Judging from results of Gd-DTPA^2 dose dependency in the intact brain and the BBB permeabilized brain, Gd-DTPA^2 could not have leaked out from the capillaries in the cortex,thalamus or SFO, but it could have been extravasated in the posterior lobe of the pituitary gland. The longitudinal (T_1) relaxation time of water in the SFO region was measured by inversion-recovery magnetic resonance imaging at 4.7 T. The T_1 relaxation rates (1/T_1) before and after Gd-DTPA^2 infusion were 0.70 ^^+__-0.02s^<-1> (mean ^^+__- SEM, n=9) and 1.53 ^^+__- 0.11s^<-1> (n=9), respecitively. The rate constant for water influx to the capillaries was estimated to be 0.84 ^^+__- 0.11s^<-1> (n=9) which corresponds with a diffusive membrane permeability (Pd) of 3.7 x 10^<-3> cm s^<-1>. Compared with values found in the literature available on this subject, this Pd value of the capillaries in SFO was the same order as that of transmembrane permeability of water of the vasa recta, and it may be 10 - 100 times larger than that of the blood-brain barrier in the cortex. Areas of the cortex and thalamus showed minimal changes in T_1 relaxation rate (ca. 0.09s^<-1>), but these were not statistically significant, which corresponds to Pd values much smaller than that found in the SFO. From these results, we conclude that the capillaries in SFO have one of the highest water permeability values among all of the capillaries in SFO have one of the highest water permeability values among all of the capillaries in the brain. It is also suggested that this magnetic resonance imaging, based on T_1 relaxation rate, is a useful method to detect local water permeability in situ