Endothelium dependent and independent mechanisms of vasorelaxant activity of synthesized 2,5-disubstituted-1,3,4-oxadiazole derivatives in rat thoracic aorta-ex vivo and molecular docking studies

Background: Vasoconstriction is a major pathological feature of cardiovascular diseases involving endothelium dependent and independent mechanisms. Oxadiazole moiety appeared to be effective in various pathologies. Objective: The aim of the study was to synthesize and evaluate the mechanism of vasorelaxation exhibited by synthesized oxadiazole derivatives. Method: The 2,5-disubstituted-1,3,4-oxadiazole derivatives were synthesized by an efficient and simple method. The derivatives were investigated for their ex-vivo vasorelaxant action on intact/denuded endothelium rat aortic rings precontracted with norepinephrine/phenylephrine/KCl. Results: The contractions induced in the aortic rings by the addition of cumulative concentrations of norepinephrine, phenylephrine, KCl and calcium were significantly antagonized by a derivative, OXD-Z2. In another experiment, verapamil pretreatment inhibited phenylephrine and Ca²⁺-induced aortic contractions and OXD-Z2 did not alter verapamilinduced inhibition. This indicated the role of L-type Ca²⁺-channels in the OXD-Z2-induced vasorelaxation via inhibition of calcium influx. Further, atropine (muscarinic receptor antagonist), L-NAME (NO synthase inhibitor) and methylene blue (non-selective cGMP inhibitor) inhibited OXD-Z2-induced relaxation in other sets of experiments. These results indicate that OXD-Z2 also mediates vasorelaxation through NO release by muscarinic receptor activation. In addition, the molecular docking studies showed that OXD-Z2 interacts with L-type Ca²⁺-channel, muscarinic (M2) receptor and eNOS. Conclusion: Thus, it is deduced from the above findings that the vasorelaxant activity of OXD-Z2 involves muscarinic receptor-mediated nitric oxide release in addition to direct inhibition of L-type Ca²⁺-channels.