Background and Objective: Cardiovascular disorders are amongst the most prevalent complications of diabetes mellitus in long term. Since vascular responsiveness to vasoactive agents changes in diabetes with time, this experimental study was conducted to evaluate time-dependent changes in the responsiveness of thoracic aorta of diabetic rats to the flavonoid quercetin.

Methods: For this purpose, male wistar rats were divided into control and experimental groups. For induction of diabetes, streptozotocin (i.p.) was used. The body weight and serum glucose parameters were determined before and at 2^nd, 4^th, and 8^th weeks after the experiment. Contractile responsiveness to KCl and noreadrenalin (NA) and quercetin-induced vasorelaxation were measured at 4^th and 8^th weeks.

Results: The results showed that after 4 and 8 weeks, quercetin (0.1 μM-1 mM) induced a dose-dependent vasorelaxation in aortic rings precontracted with KCl and/or NA from both control and diabetic groups. Furthermore, this vasorelaxation was significantly attenuated in diabetic group eight weeks after the study in comparison with data at fourth week.

Conclusion: It can be concluded that the vasorelaxant effect of this flavonoid is attenuated in diabetes mellitus with time.