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Luteolin improves vasorelaxation in aorta exposed to high glucose via NOS‐NO pathway

Luteolin (Lut, 3',4',5,7‐tetrahydroxyflavone), the main flavonoid of Flos Chrysanthemi which is a popular traditional Chinese medicinal herb, has been demonstrated to attenuate myocardial ischemia‐reperfusion injury and cause vasorelaxation. The objective of the present study was to explore the effect of luteolin (Lut) on endothelium‐dependent vasorelaxation in isolated rat aortic rings exposed to high glucose, and its underlying mechanism. Male Sprague‐Dawley rats were killed by cervical dislocation. The thoracic aorta was rapidly dissected out and the effect of Lut on tension of aortic rings pretreated with 44 mmol/L glucose for 4 h was measured isometrically on the organ bath system. We found that pretreatment with high glucose (44 mmol/L glucose for 4 h) decreased acetylcholine (ACh)‐induced endothelium‐dependent vasorelaxation. However, high mannitol (33 mmol/L mannitol + 11 mmol/L glucose) had no effect on vasorelaxation. Lut (0.7~89.6 μmol/L) evoked a concentration‐dependent relaxation in aortic rings pre‐contracted by phenylephrine (PE), and the pD2 value was 5.21±0.04. EC50 concentration of Lut markedly attenuated the inhibition of vasorelaxation induced by high glucose, which was significantly weakened by pretreatment with L‐NAME (0.1 mmol/L) for 30 min, but not by indomethacin (0.01 mmol/L). The results indicate that the decrease of endothelium‐dependent vasorelaxation in rat aortic rings exposed to high glucose was not related to high osmolarity, whereas Lut markedly attenuated this decrease of vasorelaxation which may be mediated by maintaining the activity of NOS‐NO pathway.