The Studies Of The Mechanism And The Effects Of Simulated Microgravity On Lung Circulation In Rats

ObjectiveIn this study, the tail-suspension rats will be used as animal model of simulated microgravity and the effects of simulated microgravity on lung circulation will be observed. Based on the results, we will probe into the underlying mechanisms. Our work will provide the academic evidence of establishing the countermeasure protocol in the future.Methods1. Male wistar rats were randomly assigned into 3 groups: control group, 7d tail-suspension group and 14d tail-suspension group. Tail suspension (-30°) was used to simulate the physiological effects of microgravity. The Experiments were as follows:·To detect blood gases and peripheral blood (including WBC, N and Hb) exsanguinated from left ventricular and carotid arteries·To observe the changes of morphology in lung tissues and blood vessels by HE staining, optics-microscope, transmission electron microscope, immunohistochemistry, lung capillary vessels perfusion and so on.·To detect pulmonary haemodynamics using venous and arterial cannula in rats and calculate cor-dextrum pachynsis index.·To detect the pressure of lung circulation, flow volume, pulmonary vascular resistance by isolated lung perfusion technique.·TBX₂, ET, ADM, ET-1, ANP activity in the lung tissues and peripheral blood were detected with the methods of immunohisochemistry, radio-immunity, in-situ hybridization and semi-quantitative polymerase chain reaction.2. Male wistar rats were randomly assigned into 3 groups: control group, 7d tail-suspension group and ligustrazine countermeasure group (once every day, the dose is 1.5mg/kg for one rat). Tail-suspension (-30°) was used to simulate the physiological effects of microgravity. The Experiments were as follows:·The dynamic expression of C-fos, C-jun, Calcinurein-βand Captain-2 in the lungtissue were measured by immunohisochemical technique, in-situ hybridization andWestern blotting.Results1. Through the detection of arterial blood gases, PaO₂ and SaO₂ of TS7d and TS14d rats were obviously lower than those of CON rats, the statistical difference was significant((P<0.05), while pH,PaCO₂,HCO3^-and TCO₂ had no obvious difference compared with control group(P>0.05). In the results of peripheral blood, there was only WBC which was higher in TS7d rats compared with that of CON rats.2. The results of lung morphology by HE staining showed that there were small amount of inflammatory cells infiltrated the lung tissue interstitial and the pulmonary alveoli layer was widened in the TS rats. The pulmonary alveolar wall of CON rats was thin and intact. Lamellar bodies in the tapeΠpneumocytes did not show any sign of evacuation. Ultrastructurally, the endothelial cells of intra-acinar pulmonary arteries of TS rats appeared hyperplasia and degeneration. The internal elastic laminar were irregular. The smooth muscle cells were hypertrophy. The pericytes were hyperplasia in TS7d and TS14d groups.3. Compared with the control group, the mean pulmonary arterial pressure and pulmonary vascular resistance in supine position were increased significantly after 7d TS(P<0.05), but the mean pulmonary venous pressure was also increased insignificantly. Pulmonary flow was decreased significantly (P<0.05); There were no significant difference between the results of TS14d and that of control. All the results(including mPAP,mPVP,PF and PVR) of head-down position were increased compared with that of supine position. The results of mPAP, mPVP and PF were increased significantly(P<0.05), PVR was increased insignificance (P>0.05) . The results of TS14d were increased insignificantly except mPAP, which was rised significantly(P<0.05). Moreover, the right ventricular hypertrophy index in TS7d and 14d groups were no significant difference compared with that of control group (P > 0.05) .4. Compared with the control group ,the changes of the isolated pulmonary perfusion pressure was decreased significantly in TS7d and TS 14d groups (P<0.05, P<0.01) , it was also observed that the contractile responses of pulmonary artery to phenylephrine(PE) was decreased significantly (P<0.05) after TS14d, while the vasodilation responses to acetylcholine(Ach) and sodium nitroprusside(SNP) were significantly enhanced ( P<0.01 , P<0.05 ) , meanwhile pulmonary vascular resistance(PVR) was decreased significantly in TS7d and TS14d groups (P<0.05) .5. The concentration of TBX₂, 6-keto-PGF1a and ADM in blood and lung tissues of TS7d and TS14d rats increased significantly (P<0.05, P<0.01), while the active level of ET-1 and ANP were decreased significantly (P<0.05, P<0.01). The protein expression of ADM,bFGF in lung tissue of TS7d group increased significantly(P<0.05), But the expression and the activation level of ADM in TS14d decreased less than that of TS7d group, especially for the result of ADM (P<0.05).6. Compared with control, the expression of C-fos, C-jun, Calcinurein-βand Captain-2 in lung tissue were increased, and the difference had statistical significance (P<0.01, P<0.05) in TS7d group, but the expression in the ligustrazine countermeasure group decreased significantly compared with those of TS7d(P<0.05).Conclusion1. PaO₂ and SaO₂ were decreased obviously in TS7d and 14d rats, which will induce the exchanging disturbance and result in hypoxemia. The WBC of peripheral blood was increased.2. The pathologic damage mainly manifested in the respiration of the lung tissue after TS7d and TS14d. The results suggested that pulmonary vascular structural remodeling was an important pathologic basis of lung injury and the dysfunction of pulmonary circulation after simulated microgravity induced by TS7d and TS14d.3. The pulmonary arterial pressure, pulmonary venous pressure and pulmonary vascular resistance were increased in tail-suspension rats, while pulmonary flow was decreased.4. The isolated pulmonary artery perfusion pressure and the contractile responses of pulmonary artery were attenuated and the vasodilation responses were increased after simulated microgravity. Moreover, the isolated perfusion PVR was decreased in TS rats. The impaired regulatory function of pulmonary artery may contribute to varied intolerance.5. There are many reasons for the changes of pulmonary haemodynamics and pulmonary vascular reactivity in tail-suspension rats. The abnormal expression of TBX₂, 6-Keto-PGF₁ a, ET-1, ANP, ADM, FGFb may play critical roles in the dysfunction of pulmonary circulation after simulated microgravity induced by tail-suspension in rats.6. The expression level of C-fos, C-jun, Calcinurein-βand Captain-2 in lung tissue increased obviously in tail-suspension rats, while ligustrazine countermeasure can decrease the higher expression in TS7d rats, which suggested that ligustrazine could effectively prevent acute lung injury in tail-suspension rats.