The plateau pika (Ochotona curzoniae), one of the endemic rodents inhabiting in Qinghai-Tibet plateau, has adapted well to extreme hypoxic and cold environments. Blunted hypoxic pulmonary vasoconstriction (bHPV) plays an important role on preventing plateau pika from injury induced by hypoxia. To investigate the histochemical basis of bHPV, we examined the structural morphology and immunohistochemistry of pulmonary microvessels from the fetus, pups and adults plateau pikas. The results with Kunming mouse as the comparison species showed that the double elastic lamina was less than 25% of the circumference, suggesting there is no significant muscularization of the pulmonary microvessels (10-200μm in diameter) in plateau pika against hypoxia stress, as the ratio of medial thickness to external diameter (MT/ED) of pulmonary microvessels (of 10-50, 50-100 and 100-200μm diameter) decreased in response to the prolonged hypoxia exposure in plateau pika. In the adults, plateau pika showed a lower MT/ED10-50 than Kunming mouse did (P <0.05), but no significant difference was found in MT/ED50-100 and MT/ED100-200 between two species. In pulmonary arteriole of 10-50μm diameter, higher ratio of microvascular staining with α-SMA to microvascular staining with CD31 (SMC/EC) was detected over time in plateau pika and Kunming mouse. In comparison to Kunming mouse, obviously lower SMC/EC (P < 0.01) was observed in plateau pika at each developmental period. These results suggest that a decrease in development of smooth muscle cells in pulmonary microvessels of 10-50μm diameter probably play an important role in blunting hypoxic pulmonary vasoconstriction in plateau pika.

低氧性肺血管收缩反应钝化（blunted Hypoxic Pulmonary Vasoconstriction, bHPV）是高原鼠兔在进化过程中形成的对低氧环境的一种适应性策略。以胎儿期、幼龄期及成年期高原鼠兔和昆明白小鼠为研究对象，对两者的肺组织进行发育生物学、比较组织学和比较组织化学研究，以探讨高原鼠兔bHPV形成的组织形态学基础。结果表明：（1）高原鼠兔各时期肺组织微血管的双层弹性纤维含量均低于25%，无明显肌化现象；（2）高原鼠兔直径10~50 μm、50~100 μm和100~200 μm微血管的中膜肌层厚度与其外径比（MT/ED）随年龄增加而逐渐下降；成年高原鼠兔的肺组织微血管MT/ED10-50显著低于成年昆明白小鼠（P < 0.05），但MT/ED50-100和MT/ED100-200均无明显的种间差异（P > 0.05）；（3）在直径10~50 μm直径范围微血管中，高原鼠兔和昆明白小鼠平滑肌细胞数与内皮细胞数的比值（SMC/EC）均随年龄增长呈上升趋势，且高原鼠兔SMC/EC的比值极显著低于同年龄组的昆明白小鼠（P < 0.01）。导致高原鼠兔bHPV发生的组织学基础可能是其肺组织中直径10~50μm微血管平滑肌细胞数量少。