Ryan U S, Ryan J W, Smith D S, Winkler H
Tissue Cell. 1975;7(1):181-90. doi: 10.1016/s0040-8166(75)80015-2.
Little is known of how adrenal hormones pass from the interstitial to the vascular space. We have begun to examine the adrenal endothelium as a barrier to hormone passage, by the freeze-fracturing technique. The endothelium of both cortex and medulla is fenestrated. Fractures from both regions show endothelial cells to be extremely thin in regions where fenestrations are abundant. En face fractures show fenestrae disposed in tracts; the fenestrae reaching a distribution of 35/mu2. In both cortex and medulla there are areas of continuous endothelium which contain caveolae. Structures believed to represent fenestra diaphragms contain randomly disposed particles and occasional pits. We have not identified in replicas the central ring and pore described in thin-sectioned material (Elfvin, 1965). The main differences between freeze-fractured aspects of cortical and medullary endothelium are the greater abundance of caveolae in the medulla and the size of the fenestrae (fenestra rims in the medulla are 525-780 A in diameter; in the cortex 570-1660 A). These differences may reflect the different embryological origins of the medulla and cortex. While caveolae may participate in hormone transport, there is no evidence for this. In the medulla the caveolae are more numerous and may have a function not necessarily related to transport. Possibly, caveolae play a role in processing hormones and related substances. For example, ATP and specific proteins are released as well as epinephrine during exocytosis from chromaffin cells. Epinephrine enters the vascular space but ATP does not. ATPase enzymes are a common feature of caveolae of other endothelia and may occur as well in adrenal endothelium.
关于肾上腺激素如何从间质传递到血管腔，人们了解甚少。我们已开始通过冷冻断裂技术，将肾上腺内皮作为激素传递的屏障进行研究。皮质和髓质的内皮均有窗孔。来自这两个区域的断裂面显示，在窗孔丰富的区域，内皮细胞极其薄。正面断裂显示窗孔呈束状分布；窗孔的分布密度为35/μm²。在皮质和髓质中都有连续内皮的区域，其中含有小窝。据信代表窗孔隔膜的结构含有随机分布的颗粒和偶尔的小孔。我们在复制品中未发现薄切片材料中描述的中央环和孔（埃尔夫文，1965年）。皮质和髓质内皮冷冻断裂面的主要差异在于，髓质中的小窝更为丰富，且窗孔大小不同（髓质中窗孔边缘的直径为525 - 780埃；皮质中为570 - 1660埃）。这些差异可能反映了髓质和皮质不同的胚胎起源。虽然小窝可能参与激素运输，但尚无证据支持这一点。在髓质中，小窝数量更多，可能具有不一定与运输相关的功能。小窝可能在处理激素和相关物质方面发挥作用。例如，在嗜铬细胞的胞吐过程中，ATP、特定蛋白质以及肾上腺素都会释放出来。肾上腺素进入血管腔，但ATP不会。ATP酶是其他内皮细胞小窝的共同特征，肾上腺内皮中可能也存在。
