Ley K, Arfors K E
Microvasc Res. 1986 Jan;31(1):84-99. doi: 10.1016/0026-2862(86)90009-9.
An intravital microscopic method for quantitative measurement of interstitial concentrations of fluorescent tracers has been applied to the investigation of microvascular permeability in the hamster cheek pouch. Some nanoliters of FITC-dextran mean mol wt (Mw) 20,000, 3000, or sodium fluorescein (Mw 376) were injected into an arteriole of the exposed cheek pouch via micropipet. The extravasation of fluorochromes was measured by a photodensitometric method including two sets of calibration procedures (in vitro and in vivo). Postcapillary and collecting venules exhibited the highest absolute increase of fluorochrome concentration in the tissue for all tracer molecules tested when compared to arterioles or capillaries. The permeability of the vascular wall was quantified, assuming that diffusion processes play the main role for the transport of the investigated molecules under the experimental conditions of a high concentration gradient across the membrane. Permeability coefficients P (cm/sec) and apparent diffusion coefficients D' (cm2/sec) of the microvascular wall were calculated using a mathematical model for one-dimensional diffusion in composite media. The analysis is based on measured data of interstitial diffusion coefficients of the tracers used. For all tracer molecules tested, the wall of the capillaries and postcapillary venules was significantly more permeable than the arteriolar wall. For the largest test molecule (FITC-dextran Mw 20,000), the permeability coefficient of the vessel wall showed a maximum in the postcapillary venules. These findings support the concept of a "gradient of permeability" with a nonuniform distribution of exchange capacity only for the precapillary microvessels. A marked preponderance of venular over capillary permeability could, if at all, only be detected for FITC-dextran Mw 20,000. The present study characterizes the vessel wall by apparent diffusion coefficients which are, for FITC-dextran Mw 3000, and free fluorescein, roughly three orders of magnitude lower than the apparent diffusion coefficients in connective tissue.
一种用于定量测量荧光示踪剂间质浓度的活体显微镜方法已被应用于研究仓鼠颊囊的微血管通透性。通过微量移液器将几纳升平均分子量（Mw）为20,000、3000的异硫氰酸荧光素葡聚糖或荧光素钠（Mw 376）注入暴露的颊囊的小动脉中。通过包括两组校准程序（体外和体内）的光密度测定法测量荧光染料的外渗。与小动脉或毛细血管相比，对于所有测试的示踪剂分子，毛细血管后和集合小静脉在组织中荧光染料浓度的绝对增加最高。在跨膜高浓度梯度的实验条件下，假设扩散过程对所研究分子的运输起主要作用，对血管壁的通透性进行了量化。使用复合介质中一维扩散的数学模型计算微血管壁的通透系数P（cm/秒）和表观扩散系数D'（cm2/秒）。该分析基于所使用示踪剂的间质扩散系数的测量数据。对于所有测试的示踪剂分子，毛细血管和毛细血管后小静脉的壁比小动脉壁的通透性明显更高。对于最大的测试分子（Mw 20,000的异硫氰酸荧光素葡聚糖），血管壁的通透系数在毛细血管后小静脉中显示出最大值。这些发现支持了“通透性梯度”的概念，即仅对于毛细血管前微血管，交换能力分布不均匀。如果有的话，只有对于Mw 20,000的异硫氰酸荧光素葡聚糖，才能检测到小静脉通透性明显高于毛细血管通透性。本研究通过表观扩散系数对血管壁进行了表征，对于Mw 3000的异硫氰酸荧光素葡聚糖和游离荧光素，其表观扩散系数比结缔组织中的表观扩散系数低约三个数量级。
