The present study intended to describe in detail the several blood vessels harboring special regulatory devices in rabbit’s pulmonary tissue using light and electron microscopy and immuno-histochemistry. Numerous throttle arteries were recorded within the adventitia of the segmental and sub-segmental bronchi and within pulmonary pleura. These arteries showed characteristic narrow or obliterated lumens and some of them bear longitudinal muscular intimal bolsters. For the first time, TEM revealed some structural modifications of the vascular endothelial cells of these arteries indicating that they become more activated to perform some additional functions. Arteriovenous anastomoses (AVAs) including direct shunt vessels and glomus organs were also recognized. Direct arteriovenous shunts appeared as small connecting devices communicating between small arteries and small veins while glomus organs consisted of the tortuous glomus vessels and the related afferent and efferent vessels. Several arteries and veins showing unique unusual structural characteristics were also described. For the first time, serotonin (5-HT) was strongly expressed in the vascular endothelium and muscle fibers of throttle arteries, in glomus cells of the glomus vessels, and in vascular endothelium of some veins and venules of special structure. The exact role of 5-HT is still unknown and further investigations are required to determine the types and distribution of 5-HT receptors present in these vascular devices. We concluded that these special vascular devices can play a critical role in controlling blood flow and pressure in the peripheral pulmonary circulation; however, the exact physiological mechanisms by which they work or are controlled remain unknown providing a ripe area for further investigation.

中文翻译：

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兔外周肺循环特殊调节装置的结构和功能特点

本研究旨在使用光学和电子显微镜以及免疫组织化学详细描述兔子肺组织中含有特殊调节装置的几种血管。在节段和亚节段支气管的外膜和肺胸膜内记录了许多节流动脉。这些动脉显示出特征性的狭窄或闭塞的管腔，其中一些带有纵向的肌肉内膜垫。TEM 首次揭示了这些动脉的血管内皮细胞的一些结构改变，表明它们变得更加活跃以执行一些额外的功能。动静脉吻合术 (AVA) 包括直接分流血管和血管球器官也被识别。直接动静脉分流作为小动脉和小静脉之间的小连接装置出现，而血管球器官由曲折的血管球血管和相关的传入和传出血管组成。还描述了一些显示独特异常结构特征的动脉和静脉。5-羟色胺(5-HT)首次在节流动脉的血管内皮和肌纤维、血管球细胞以及一些特殊结构的静脉和小静脉的血管内皮中强烈表达。5-HT 的确切作用仍然未知，需要进一步研究以确定这些血管装置中存在的 5-HT 受体的类型和分布。我们得出结论，这些特殊的血管装置可以在控制外周肺循环的血流和压力方面发挥关键作用；然而，它们工作或控制的确切生理机制仍然未知，为进一步研究提供了一个成熟的领域。