Aim To study the diastolic effect and mechanism of farrerol on isolated pulmonary arteries of C57BL/6J mice. Methods After anesthesia, mouse lung tissue was quickly removed and placed into the 4 ℃ K-H buffer, pulmonary arteries were isolated under the microscope and cut into 2 mm long vascular rings for spare use. (1)The effect of farrerol on the resting tension of isolated mouse pulmonary arteries:in the resting state, the active mouse pulmonary artery rings were treated with different concentrations of farrerol (10－6,3×10－6,0－5,3×10－5 and 10－4 mol/L). (2)Farrerol relaxed mouse pulmonary artery experiment:pulmonary arteries were contracted using phenylephrine (PE, 1 μmol/L) or KCl (60 mmol/L), and when the contraction reached the platform, different concentrations of farrerol (10－6,3×10－6,0－5,3×10－5 and 10－4 mol/L) was added. (3) Farrerol inhibited pulmonary artery contraction experiment:under conditions with or without the addition of farrerol, pulmonary arteries were contracted using different concentrations of PE (10－9,3×10－9,0－8,3×10－8,0－7,3×10－7 and 10－6 mol/L) or KCl (0,0, 0,0, 80 and 120 mmol/L), and the pulmonary artery muscle tension was recorded. (4)Calcium free and recalcification experiments:under conditions with or without the addition of farrerol, the changes of isolated mouse pulmonary artery tension were measured in the state of calcium free or recalcification {2.5 mmol/L [Ca²＋]ex}. (5)The relationship between farrerol induced relaxation of isolated mouse pulmonary arteries and potassium ion channels:firstly, 60 mmol/L KCl solution was used to contract the mouse pulmonary arteries until the platform. Then, 3 mmol/L aminopyridine (4-AP), 2 mmol/L tetraethylammonium (TEA), 30 μmol/L BaCl₂, and 10 μmol/L glibenclamide (Gli) were added and treated for 15 min. Subsequently, the pulmonary arteries were relaxed using a concentration gradient of farrerol. Results Farrerol had no significant effect on the mouse pulmonary arteries in the resting state, but had a concentration-dependent relaxing effect on the mouse pulmonary arteries pre-contracted with PE and KCl. While the pretreatment of 3×10－5 mol/L farrerol could significantly reduce the maximum contraction of mouse pulmonary arteries induced by PE and KCl (P＜0.01), as well as significantly reduce the contraction of mouse pulmonary arteries induced by KCl under calcium free or recalcification conditions (P＜0.01). Addition of the voltage-dependent potassium ion channel blocker 4-AP significantly reduced the maximum diastolic rate of mouse pulmonary arteries induced by farrerol (P＜0.01), while addition of the high conductivity calcium activated potassium ion channel blocker TEA, inward rectifying potassium ion channel blocker BaCl₂, or ATP sensitive potassium ion channel blocker Gli had no significant effect on the vasodilation effect of farrerol (P＞0.05). ConclusionFarrerol has a relaxing effect on isolated mouse pulmonary arteries, and its mechanism may be related to open voltage-dependent potassium ion channels.