Royal jelly causes hypotension and vasodilation induced by increasing nitric oxide production

Among royal jelly's (RJ) various biological activities, its possible antihypertension and vasorelaxation effects deserve particular attention, but the underlying mechanisms of action remain unclear. Therefore, this study used the spontaneously hypertensive rats (SHR) hypertension model and the isolated rabbit thoracic aorta rings model to explore the mechanisms underlying the hypotension and vasorelaxation effects of RJ. Rats were divided into the following groups (n=6): WKY-control group, SHR-control group, and SHR-RJ group. SHR-RJ group was received 1g/kg of RJ via oral administration daily for 4weeks. Systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and nitric oxide (NO) level were detected. In addition, the mechanism of vasodilation of RJ was investigated using an isolated rabbit aortic ring technique. RJ significantly reduced SBP and DBP as well as increased NO levels of SHR in vivo. RJ caused vasorelaxation of the isolated aorta rings, and this effect was inhibited by atropine (M-3 receptor blocker), L-NAME (nitric oxide synthase inhibitor), methylene blue (guanylate cyclase inhibitor), and indomethacin (cyclooxygenase inhibitor). Moreover, RJ could markedly suppress the NE-induced intracellular Ca2+ releases and high K+-induced extracellular Ca2+ influx in denuded aortic rings. In addition, RJ can also increase cGMP levels and the production of NO in isolated aortic rings. The present study showed that RJ has antihypertensive effects and was associated with increased NO production. In addition, RJ contains muscarinic receptor agonist, possibly an acetylcholine-like substance, and induces vasodilation through NO/cGMP pathway and calcium channels.