Faarup P, Holstein-Rathlou N H, Hegedüs V
University Institute of Molecular Pathology, Copenhagen, Denmark.
APMIS. 2000 Nov;108(11):779-84. doi: 10.1034/j.1600-0463.2000.d01-29.x.
In spite of the very high exchange of water and solutes between the proximal tubules and the peritubular capillaries, very little is known about flow directions in these two interrelated structures. We therefore developed a morphological technique suitable for the quantitative evaluation of a counter-current system between the proximal convoluted tubules and the peritubular capillaries in rat renal cortex.
In male pentothal-anesthetized Wistar rats (body weight 200-250 g), India ink was injected into the aorta above the renal arteries, followed by instant freezing of the right kidney in isopentane at -165 degrees C, and subsequent freeze-substitution in alcohol. In microscopic slides from kidneys in which only 20-55% of the cortical peritubular capillary loops was filled with ink--representing the arterial end of the capillaries--and in which the proximal tubular segmentation could be identified in PAS-stained sections, the segments of the convoluted proximal tubules were quantitatively compared with regard to the presence of ink-stained and unstained peritubular capillaries in nephrons from the whole renal cortex.
In the microscopic specimens of the five animals used both the loops from the first segment (P1) of the proximal convoluted tubule and those of the second segment (P2) were systematically packed closely together, the transitional segment (P1-2) being interposed between the groups. Around the loops of P1, 8%+/-2% of the capillaries was stained with India ink. In contrast, surrounding the P2 loops 67%+/-5% of the capillaries contained ink, significantly exceeding that for P1 (p<0.01).
Throughout the rat renal cortex, the most proximal fraction of the peritubular capillaries surrounds the second segments of the proximal convoluted tubules, while the first tubular segments are surrounded by the more distal fraction of the peritubular capillaries. Consequently, the flows in the peritubular capillaries and in the proximal convoluted tubules in the rat renal cortex are systematically arranged as a counter-current system. This feature was previously identified only in superficial nephrons.
尽管近端小管和肾小管周围毛细血管之间水和溶质的交换非常活跃，但对于这两个相关结构中的血流方向却知之甚少。因此，我们开发了一种形态学技术，适用于定量评估大鼠肾皮质近端曲管和肾小管周围毛细血管之间的逆流系统。
对雄性硫喷妥钠麻醉的Wistar大鼠（体重200 - 250克），将印度墨汁注入肾动脉上方的主动脉，随后将右肾在-165℃的异戊烷中立即冷冻，接着在酒精中进行冷冻置换。在肾组织切片中，仅20 - 55%的皮质肾小管周围毛细血管环充满墨汁（代表毛细血管的动脉端），且在PAS染色切片中可识别近端小管节段，对整个肾皮质肾单位中曲部近端小管节段周围墨汁染色和未染色的肾小管周围毛细血管的存在情况进行定量比较。
在使用的5只动物的显微镜标本中，近端曲管第一段（P1）和第二段（P2）的毛细血管环都系统地紧密排列在一起，过渡段（P1 - 2）介于两组之间。在P1段的毛细血管环周围，8%±2%的毛细血管被印度墨汁染色。相比之下，在P2段毛细血管环周围，67%±5%的毛细血管含有墨汁，显著超过P1段（p < 0.01）。
在整个大鼠肾皮质中，肾小管周围毛细血管的最近端部分围绕近端曲管的第二段，而第一段肾小管则被肾小管周围毛细血管的更远端部分所围绕。因此，大鼠肾皮质中肾小管周围毛细血管和近端曲管中的血流系统地排列为逆流系统。这一特征以前仅在浅表肾单位中被发现。
