Morphological changes and molecular mechanism in the carotid bodies after the termination of chronic hypoxia

低氧暴露2、4、8周后颈动脉小体短轴与常氧对照组相比增大1.2 ~ 1.5倍，长轴与常氧对照组相比增大1.3 ~ 1.7倍。扩大的颈动脉小体包含许多扩张的血管。低氧暴露4周后，颈动脉小体中P物质（SP）和降钙素基因相关肽（CGRP）纤维的平均密度短暂升高，8-12周后下降。血管活性肠多肽（VIP）纤维密度在观察到的缺氧暴露的所有时期均显著增加，在暴露4周后尤其高。在缺氧条件下，颈动脉小体中神经肽Y纤维的密度没有变化。这些特征变化提示，在每四个缺氧期后，这些含神经肽纤维在颈动脉小体中的作用可能有所不同。在颈动脉小体中，经过8周的缺氧暴露后，直径小于5 μm的小血管比例下降到20%以下，直径大于16 μm的小血管比例增加到20%以上。慢性缺氧结束后1周和2周颈动脉小体缩小，但其短轴和长轴仍比正常对照组大。慢性缺氧终止后4周和8周均降至接近正常对照水平。慢性缺氧结束后8周，约45%的血管为直径小于5 μm和10 μm的小血管。直径大于16 μm的较大血管所占比例小于10%。缺氧终止后4周，颈动脉小体内NPY纤维密度增加

The carotid bodies after 2, 4, and 8 weeks of hypoxic exposure were enlarged by 1.2-1.5 times in the short axis, and 1.3-1.7 times in the long axis in comparison with the normoxic control ones. The enlarged carotid bodies contained a number of expanded vasculatures. Mean density of substance P (SP) and calcitonin gene-related peptide (CGRP) containing fibers was transiently high in the carotid bodies after 4 weeks hypoxic exposure, and decreased in those after 8-12 weeks exposure. Density of vasoactive intestinal polypeptide (VIP) fibers increased significantly in all periods of hypoxic exposure observed, and was especially high in those after 4 weeks exposure. Density of neuropeptide Y fibers was unchanged in the carotid bodies during hypoxic exposure. These characteristic changes suggest a possibility that the role of these neuropeptide containing fibers may be different in the carotid bodies after each of four periods of hypoxic exposureIn the carotid bodies after 8 weeks of hypoxic exposure, the percentage of small vessels with diameters less than 5 μm decreased to under 20%, that of diameters greater than 16 μm increased to over 20%. The carotid bodies 1 and 2 weeks after the termination of chronic hypoxia were diminished in size, although their short and long axes remained larger than the normoxic controls. Those 4 and 8 weeks after the termination of chronic hypoxia were diminished to nearly normoxic control level. In those 8 weeks after the termination of chronic hypoxia, about 45% of the blood vessels were small ones with diameters less than 5 μm and 10 μm. The percentage of relatively large vessels with diameters greater than 16 μm was less than 10%. In the carotid bodies 4 weeks after the termination of hypoxia, the density of NPY fibers increased