[Reactivity of pulmonary arteries and thoracic aortae in rats under tail-suspension and the effects of NOS inhibitor].
OBJECTIVE: To further disclose mechanisms in adaptation of pulmonary and systemic arteries to simulated microgravity (SM), so as to elucidate the mechanisms accounting for orthostatic intolerance after SM, and to explore a new kind of countermeasure for orthostatic intolerance. METHOD: 300 tail suspended (TS) rats were used as the model to simulate the physiological effects of microgravity. Vasoreactivity changes of rings sectioned from pulmonary artery (PA) and thoracic aorta (TA) to 68 mmoles/L KCl, plus phenylephrine (PE) and acetylcholine (ACh) were observed after 7 d and 14 d tail-suspension. After preconditioning with 10(-5) moles/L N-nitro-L-arginine methyl ester (L-NAME) for 20 min, vasoreactivity changes of PA and TA to PE and ACh were respectively repeated. RESULT: The contractile responsiveness of PA and TA to KCl and PE decreased significantly or very significantly after TS7 d and TSI4 d. The dilatory reactivity of PA and TA to ACh after TS7 d had a significant or very significant increase, but reactivity of PA showed no change and TA showed only a tendency to increase after TS14 d. After preconditioning with 10(-5) moles/L L-NAME, responsiveness of PA to PE after TS7 d and TS14 d had no difference among the three groups, but responsiveness of TA to PE after TS7 d and TS14 d had a significant decrease. The dilatory reactivity of PA after TS7 d decreased significantly or very significantly, and the remains showed no significant change. CONCLUSION: The decrease of contractile responsiveness of PA and TA might be due to the increased dilatory function of the endothelial cells. The fact that 10(-5) moles/L L-NAME reversed the decrease of contractile responsiveness of PA and partly of TA after tail suspension implicates that there might be an inhibitory action on the dilatory function of the endothelial cells. The NOS inhibitors may be helpful in preventing orthostatic intolerance.