Physiological Response Of Respiratory And Circulatory Activities To Hypercapnia In The Unanesthetized Eospalax Baileyi And The Comparison With Rhizomys Pruinosus And Rattus Norvegicus

Plateau zokor?Eospalax baileyi?is a subterranean rodent living on Qinghai-Tibet Plateau.The gas in its tunnels is characterized by hypoxia-hypercapnia.Many studies have focused on the hypoxic adaptation mechanism,but there are few reports on the adaptation mechanism of plateau zokor to hypercapnia.In this study,using unanesthetized plateau zokor,we tested the changes in respiratory movement,blood pressure,heart rate and blood gas with inhalation of CO₂ gases and compared them with bamboo rat?Rhizomys pruinosus?and SD rat?Rattus norvegicus?.We also measured the activity of carbonic anhydrase of these three species in order to explore the physiological mechanism for the zokor to adapt to its environment with high CO₂.The results are as follows:1.Measured by whole-body plethysmography,the breathing frequency?fR?of plateau zokor was significantly lower,but the tidal volume?V_T?was significantly higher than that of SD rats?P<0.001?.This indicated that the zokor's respiration is slow and deep and this could increase its respiratory reserve.When gases with5%CO₂,5%CO₂+O₂ and 10%CO₂+O₂ were given both fR and V_T of zokor were not significantly changed compared to the air group?P>0.05?.The fR of SD rat increased significantly when the gases with 5%CO₂ and 5%CO₂+O₂ were given.However,the fR,V_T and V_E of zokor increased only with 10%CO₂?P<0.05?.This implicate that zokor can tolerate certain levels of high CO₂.2.When plateau zokor breathed gases with 5%CO₂,5%CO₂+O₂,10%CO₂ and10%CO₂+O₂,the mean arterial blood pressure?MAP?is slightly increased,and heart rate?HR?is slightly accelerated by the invasive blood pressure method,but there was no significant change compared with the baseline values?P>0.05?.When SD rats and bamboo rats breathed 10%CO₂ and 10%CO₂+O₂ gas,theirs HR decreased significantly?P<0.05?compared with the baseline values,however,there was no significant change in HR of plateau zokor.This indicated that the heart rate of plateau zokor has stronger tolerance to hypercapnia.3.The carbonic anhydrase activity in erythrocytes of plateau zokor was significantly lower than that of SD rat?P<0.05?.This could help the zokor maintain the homeostasis in the habitat with varied CO₂ concentration and may be related to the high content of CO₂ in its arterial blood.