Abstract: Abstract Objective: To investigate the effect of chronic intermittent hypobaric hypoxia (CIHH) on spontaneous contraction of rat ileum inhibited by paeonol in vitro, and the mechanism thereof. Methods: Sprague-Dawlay (SD) rats were randomly divided into normal oxygen group (CON) and CIHH treatment group (CIHH). Rats of CIHH group were exposed to hypoxia in a hypobaric chamber simulating 5000m altitude, 6 hours daily for 28 days. CON animals lived in the same environment as CIHH animals except hypoxia. Samples of rat ileum were prepared routinely. The ileum contractions were recorded using organ bath technique. Results: (1) Paeonol significantly decreased the amplitude, frequency, tension and activity of the ileam contraction in a dose-dependent manner both in CON and CIHH groups. With activity as criteria, IC50 was 65.13 mg/L and 135.74 mg/L. (2) CIHH significantly attenuated the inhibitory effects of Paeonol. (3) Paeonol inhibited acetylcholine-induced contraction of extracellular and intracellular calcium significantly in CON group. Paeonol inhibited the contraction of store-operated calcium channel (ROCC) and voltage-operated calcium channel. The inhibitory effect of Paeonol can be partly blocked by L-NAME, indomethacin and propranolol. (4) The acetylcholine-induced intracellular calcium release and ROCC-induced contraction were not blocked by Paeonol in CIHH, and which was not blocked by propranolol. Conclusion：CIHH reduced the inhibitory effects of Paeonol on rat ileum, which may be caused by the blocking of Paeonol induced ntracellular Ca2+ release, inhibiting of the ROCC and β- adrenergic receptor through CIHH.

Key words: Chronic intermittent hypobaric hypoxia, Paeonol, Rats, Ileam, Nitric oxide