[Effects of NO synthases inhibitor on cardiovascular deconditioning in rats after 7 d tail-suspension]

To disclose the changes in pathophysiology of cardiovascular deconditioning (CVD) induced by tail-suspension (TS) and to explore the effects of NOS inhibitor on CVD in TS rats.

-30 degrees tail suspended rats were used as the model to simulate the physiological effects of microgravity. Wistar rats were randomly arranged into: control group (CON), 7 d TS group (TS 7 d) and TS 7 d + NOS inhibitor group (TS 7 d + L-NAME). Then, all the rats were subjected to +90 degrees head-up tilt to simulate the physiological effects of orthostatic stress (SO) after 7 d tail-suspension, only that the TS 7d + L-NAME rats were injected with 10(-6) M L-NAME (N-nitro-L-arginine methylester) through hypoglossal vein before tilting after 7 d TS. Carotid pressure and limb II ECG were measured with a PowerLab physiological system during 120 min tilt, and mean arterial pressure (MAP) and heart rate (HR) were analysized.

Only one transient episode of hypotension-bradycardia appeared during the tilt in CON rats, but seven episodes occurred in TS 7 d rats, while the TS 7 d + L-NAME rats has only a significant increase in MAP at 10 min. No differences were found between the other parameters in recumbent position and those during the tilt.

The CVD in the rats induced by TS is relative to an increase of NO production. 10(-6) M L-NAME had an alleviating effects on the CVD, which might be due to the increase of peripheral resistance of blood vessels and the central sympathetic drive by the combination of L-NAME with NOS. The contribution of the perivascular nerves and pulmonary arteries to this effect remains to be further studied.