OBJECTIVE: To compare the difference of vasomotor functions in aortas segments from Wistar rats between 1-hour and 6-hours after exposure of water-soluble components of fine particulate matter (PM2.5). METHODS: All 30 Wistar rats were assigned to five groups (n=6 for each group) at random: the blank control group, control group for 1-hour and 6-hours, exposure group for 1-hour and 6-hours. The rats were sacrificed 1-hour or 6-hours later and aorta ring segments were mounted on wire myographs. RESULTS: (1) There was no significant difference in vasomotor functions among three control groups (P>0.05). (2) 1-hour or 6-hours after exposure there was a decrease of contraction elicited by 60 mmol/L KCl in contrast to the control group (P0.05). (3) On the level of 10(-5) or 10(-7) mol/L, 1-hour after exposure there was a decrease in endothelium-dependent acetylcholine (ACh) elicited relaxation precontracted by 10(-6) mol/L NE compared with the control group (P0.05). (3) On the level of 10(-5) or 10(-7) mol/L, 1-hour after exposure there was a decrease in endothelium-dependent acetylcholine (ACh) elicited relaxation precontracted by 10(-6) mol/L NE compared with the control group (P0.05). (3) On the level of 10(-5) or 10(-7) mol/L, 1-hour after exposure there was a decrease in endothelium-dependent acetylcholine (ACh) elicited relaxation precontracted by 10(-6) mol/L NE compared with the control group (P0.05). On the level from 10(-5) to 10(-9) mol/L, 1-hour after exposure there was a decrease in endothelium-independent sodium nitroprusside (SNP) elicited relaxation precontracted by 10(-6) mol/L NE as compared with the control group (P<0.01 or P<0.05) and a decrease on the level of 10(-6) or 10(-9) mol/L compared with the exposure group for 6-hours (P<0.05), 6-hours after exposure a decrease was caused as compared with the control group on the level from 10(-5) to 10(-7) mol/L (P<0.01 or P<0.05). CONCLUSIONS: Inhibition of contraction and impairment of relaxation in aortas should be caused 1-hour after exposure to water-soluble components of PM2.5 in the air, which is weaken 6-hours after exposure.