The in vitro effect of Melissa officinalis aqueous extract on aortic reactivity in rats with subchronic diabetes

Background and Objective: Vascular abnormality and dysfunction plays an important role in the pathogenesis of vascular disease in diabetic state. In this study, we aimed to investigate whether an in vitro exposure of endothelium-intact aortic rings to Melissa officinalis (lemon balm, MO) aqueous extract could have a beneficial effect in rats with subchronic diabetes. Materials and Methods: Diabetes was induced with a single dose of intraperitoneal injection of streptozotocin (STZ, 60?mg/kg). After one month, reactivity of isolated endothelium-intact aortic rings to KCl and phenylephrine (PE) in the absence and presence of blockers of nitric oxide synthase (L-NAME) and prostaglandin synthesis pathway (indomethacin) in addition to the role of extracellular calcium was evaluated in the presence of MO extract in a cumula-tive manner. Results: After 1 month, addition of MO extract (at a concentration range of 0.2-1 mg/ml) caused a significant concentration-dependent relaxation of phenylephrine (PE) and not KCl-preconstricted rings in both control and diabetic groups with a significant inter-group difference of p < 0.05-0.01 for the former group. Furthermore, both L-NAME (100 ?M) and not indomethacin (10 ?M) significantly diminished the vasorelaxant responses following MO addition. Meanwhile, there was no significant difference between the groups in the absence of extracellular calcium. Conclusion: These findings show that MO aqueous extract could relax the PE-preconstricted rings of aorta in STZ-diabetic rats through a nitric oxide pathway and prostaglandin pathway does not have a significant role and this extract could not affect the release of calcium from intracellular stores.