| The plateau pika(Ochotona Curzoniae), a native specie living in the Qinghai-Tibet Plateau, acclimatizes well to high altitude. Owning to its evolution in physiological mechanisms, Plateau pika is tolerant to hypoxia. As the sites for gas exchange, lung tissue services as the most important organ for mammals to maintain oxygen diffusion. Blunted hypoxic pulmonary vasoconstriction(bHPV) is one of the psychological adaptive mechanisms for coping with hypoxic environmental stress accompanying its evolution. To reveal histochemical basis of bHPV in plateau pika,we study the structural morphology and immunohistoche mistry of pulmonary microvessels. Endogenous gas molecules, NO and H2 S, are studied as well. Our results may reveal the bHPV of plateau pika, at cell and molecule level.To elucidate the histochemical basis of bHPV, we investigated the structural morphology and immunohistoche mistry of pulmonary microvessels within the fetus,pups and adults of Plateau pikas, using Kunming mice as the control model. No muscularization of pulmonary microvessels(10-200μm in diameter) was observed in both Plateau pika and Kunming mouse, as the double elastic lamina was less than25% of the circumference. We found that the ratio of medial thickness to external diameter(MVM) of pulmonary microvessels(10-50, 50-100 and 100-200μm)decreased along with the time exposed to hypoxia in Plateau pika. In the adults,Plateau pika maintained a lower MVM10-50 than Kunming mouse, but no significant difference was found in MVM50-100 and MVM100-200 between two species. As to pulmonary arteriole of 10-50μm in diameter, higher RSMC/EC was detected over time in Plateau pika and Kunming mouse. In comparison to Kunming mouse,obviously lower RSMC/EC(P < 0.05) was demonstrated in Plateau pika at each stage. Our results suggest that less smooth muscle cells in pulmonary microvessels with an outer diameter of 10-50μm probably play an important role in blunting hypoxic pulmonary vasoconstriction in Plateau pika.The content of NO decreased along with the time exposed to hypoxia in Plateau pika. In the adults, Plateau pika maintained NO at 0.82 μmol/L and in the pupswhich is 0.88 μmol/L. The content of H2 S is on the contrary, 21.4 pg/mL and 27.0pg/mL are in the pups and adults. The content of NO has growth and decline relation to the content of H2 S.To sum up, the ratio of medial thickness to external diameter(MVM) of pulmonary microvessels decreased along with the time exposed to hypoxia in Plateau pika. And our results suggest that less smooth muscle cells in pulmonary microvessels with an outer diameter of 10-50μm probably play an important role in blunting hypoxic pulmonary vasoconstriction in plateau pika. In the pups and adults,plateau pika keep the constant relatively content of NO and H2 S. It need more study about whether both of them have the growth and decline relation. |
